wip osu pp update

src/beatmap/control_points.rs

@@ -33,13 +33,52 @@ impl Default for TimingPoint {
 /// [`TimingPoint`] that depends on a previous one.
 #[derive(Copy, Clone, Debug, PartialEq)]
 pub struct DifficultyPoint {
-    /// The start time for the current speed multiplier
+    /// The time at which the control point takes effect.
     pub time: f64,
-    /// The speed multiplier until the next timing point
-    pub speed_multiplier: f64,
+    /// The slider velocity at this control point.
+    pub slider_vel: f64,
     /// Whether the section between this and the
     /// next timing points is a kiai section
     pub kiai: bool,
+    /// Legacy BPM multiplier that introduces floating-point errors for rulesets that depend on it.
+    pub bpm_mult: f64,
+    /// Whether or not slider ticks should be generated at this control point.
+    /// This exists for backwards compatibility with maps that abuse NaN
+    /// slider velocity behavior on osu!stable (e.g. /b/2628991).
+    pub generate_ticks: bool,
+}
+
+impl DifficultyPoint {
+    /// The default slider velocity for a [`DifficultyPoint`]
+    pub const DEFAULT_SLIDER_VEL: f64 = 1.0;
+    /// The default BPM multipler for a [`DifficultyPoint`]
+    pub const DEFAULT_BPM_MULT: f64 = 1.0;
+    /// The default for generating ticks of a [`DifficultyPoint`]
+    pub const DEFAULT_GENERATE_TICKS: bool = true;
+
+    /// Create a new [`DifficultyPoint`]
+    pub fn new(time: f64, beat_len: f64, speed_multiplier: f64, kiai: bool) -> Self {
+        // * Note: In stable, the division occurs on floats, but with compiler optimisations
+        // * turned on actually seems to occur on doubles via some .NET black magic (possibly inlining?).
+        let bpm_multiplier = if beat_len < 0.0 {
+            ((-beat_len) as f32).clamp(10.0, 10_000.0)
+        } else {
+            1.0
+        };
+
+        Self {
+            time,
+            slider_vel: speed_multiplier.clamp(0.1, 10.0),
+            kiai,
+            bpm_mult: bpm_multiplier as f64,
+            generate_ticks: !beat_len.is_nan(),
+        }
+    }
+
+    pub(crate) fn is_redundant(&self, existing: &DifficultyPoint) -> bool {
+        (self.slider_vel - existing.slider_vel).abs() <= f64::EPSILON
+            && self.generate_ticks == existing.generate_ticks
+    }
 }
 
 impl PartialOrd for DifficultyPoint {
@@ -52,8 +91,10 @@ impl Default for DifficultyPoint {
     fn default() -> Self {
         Self {
             time: 0.0,
-            speed_multiplier: 1.0,
             kiai: false,
+            slider_vel: Self::DEFAULT_SLIDER_VEL,
+            bpm_mult: Self::DEFAULT_BPM_MULT,
+            generate_ticks: Self::DEFAULT_GENERATE_TICKS,
         }
     }
 }
@@ -139,38 +180,30 @@ mod test {
 
     #[test]
     fn control_point_iter() {
-        let map = Beatmap {
-            timing_points: vec![
-                TimingPoint {
-                    time: 1.0,
-                    beat_len: 10.0,
-                    kiai: false,
-                },
-                TimingPoint {
-                    time: 3.0,
-                    beat_len: 10.0,
-                    kiai: false,
-                },
-                TimingPoint {
-                    time: 4.0,
-                    beat_len: 10.0,
-                    kiai: false,
-                },
-            ],
-            difficulty_points: vec![
-                DifficultyPoint {
-                    time: 2.0,
-                    speed_multiplier: 10.0,
-                    kiai: false,
-                },
-                DifficultyPoint {
-                    time: 5.0,
-                    speed_multiplier: 10.0,
-                    kiai: false,
-                },
-            ],
-            ..Default::default()
-        };
+        let mut map = Beatmap::default();
+
+        map.timing_points.push(TimingPoint {
+            time: 1.0,
+            beat_len: 10.0,
+            kiai: false,
+        });
+
+        map.timing_points.push(TimingPoint {
+            time: 3.0,
+            beat_len: 10.0,
+            kiai: false,
+        });
+
+        map.timing_points.push(TimingPoint {
+            time: 4.0,
+            beat_len: 10.0,
+            kiai: false,
+        });
+
+        map.difficulty_points
+            .push(DifficultyPoint::new(2.0, 10.0, 10.0, false));
+        map.difficulty_points
+            .push(DifficultyPoint::new(5.0, 10.0, 10.0, false));
 
         let mut iter = ControlPointIter::new(&map);
 

src/beatmap/converts/mania/pattern_generator/distance_object.rs

@@ -57,7 +57,7 @@ impl<'h> DistanceObjectPatternGenerator<'h> {
 
         // ! BUG: Since `LegacyDifficultyControlPoint` are not considered while parsing,
         // ! this value can be slightly off due to float arithmetics.
-        let beat_len = timing_point.beat_len / difficulty_point.speed_multiplier;
+        let beat_len = timing_point.beat_len * difficulty_point.bpm_mult;
 
         let span_count = (repeats + 1) as i32;
         let start_time = hit_object.start_time.round() as i32;

src/beatmap/converts/taiko.rs

@@ -111,9 +111,7 @@ impl Beatmap {
         let timing_point = self.timing_point_at(*start_time);
         let difficulty_point = self.difficulty_point_at(*start_time).unwrap_or_default();
 
-        // ! BUG: Since `LegacyDifficultyControlPoint` are not considered while parsing,
-        // ! this value can be slightly off due to float arithmetics.
-        let mut beat_len = timing_point.beat_len / difficulty_point.speed_multiplier;
+        let mut beat_len = timing_point.beat_len * difficulty_point.bpm_mult;
 
         let slider_scoring_point_dist =
             OSU_BASE_SCORING_DIST as f64 * self.slider_mult / self.tick_rate;

src/beatmap/mod.rs

@@ -7,6 +7,7 @@ pub use self::{
     breaks::Break,
     control_points::{ControlPoint, ControlPointIter, DifficultyPoint, TimingPoint},
     mode::GameMode,
+    sorted_vec::SortedVec,
 };
 
 mod attributes;
@@ -14,6 +15,7 @@ mod breaks;
 mod control_points;
 mod converts;
 mod mode;
+mod sorted_vec;
 
 /// The main beatmap struct containing all data relevant
 /// for difficulty and performance calculation
@@ -50,10 +52,10 @@ pub struct Beatmap {
     pub sounds: Vec<u8>,
 
     /// Timing points that indicate a new timing section.
-    pub timing_points: Vec<TimingPoint>,
+    pub timing_points: SortedVec<TimingPoint>,
 
     /// Timing point for the current timing section.
-    pub difficulty_points: Vec<DifficultyPoint>,
+    pub difficulty_points: SortedVec<DifficultyPoint>,
 
     /// The stack leniency that is used to calculate
     /// the stack offset for stacked positions.

src/beatmap/sorted_vec.rs

@@ -0,0 +1,90 @@
+use std::{
+    cmp::Ordering,
+    convert::identity,
+    fmt::{Debug, Formatter, Result as FmtResult},
+    ops::Deref,
+};
+
+use super::{DifficultyPoint, TimingPoint};
+
+/// A [`Vec`] whose elements are guaranteed to be in order based on the given comparator.
+#[derive(Clone)]
+pub struct SortedVec<T> {
+    inner: Vec<T>,
+    cmp: fn(&T, &T) -> Ordering,
+}
+
+impl<T> SortedVec<T> {
+    /// If the value is found then [`Result::Ok`] is returned, containing the
+    /// index of the matching element. If there are multiple matches, then any
+    /// one of the matches could be returned.
+    /// If the value is not found then [`Result::Err`] is returned, containing
+    /// the index where a matching element could be inserted while maintaining
+    /// sorted order.
+    pub fn find(&self, value: &T) -> Result<usize, usize> {
+        self.inner
+            .binary_search_by(|probe| (self.cmp)(probe, value))
+    }
+
+    pub(crate) fn push(&mut self, value: T) {
+        let idx = self.find(&value).map_or_else(identity, identity);
+
+        self.inner.insert(idx, value);
+    }
+
+    pub(crate) fn dedup_by_key<F, K>(&mut self, mut key: F)
+    where
+        F: FnMut(&mut T) -> K,
+        K: PartialEq,
+    {
+        self.inner.dedup_by(|a, b| key(a) == key(b))
+    }
+}
+
+impl<T> Deref for SortedVec<T> {
+    type Target = Vec<T>;
+
+    #[inline]
+    fn deref(&self) -> &Self::Target {
+        &self.inner
+    }
+}
+
+impl<T: Debug> Debug for SortedVec<T> {
+    fn fmt(&self, f: &mut Formatter<'_>) -> FmtResult {
+        Debug::fmt(&self.inner, f)
+    }
+}
+
+impl Default for SortedVec<TimingPoint> {
+    #[inline]
+    fn default() -> Self {
+        Self {
+            inner: Vec::new(),
+            cmp: |a, b| a.time.partial_cmp(&b.time).unwrap_or(Ordering::Equal),
+        }
+    }
+}
+
+impl Default for SortedVec<DifficultyPoint> {
+    #[inline]
+    fn default() -> Self {
+        Self {
+            inner: Vec::new(),
+            cmp: |a, b| a.time.partial_cmp(&b.time).unwrap_or(Ordering::Equal),
+        }
+    }
+}
+
+impl SortedVec<DifficultyPoint> {
+    pub(crate) fn push_if_not_redundant(&mut self, value: DifficultyPoint) {
+        let is_redundant = match self.find(&value).map_err(|idx| idx.checked_sub(1)) {
+            Ok(idx) | Err(Some(idx)) => value.is_redundant(&self[idx]),
+            Err(None) => value.is_redundant(&DifficultyPoint::default()),
+        };
+
+        if !is_redundant {
+            self.push(value);
+        }
+    }
+}

src/catch/fruit_or_juice.rs

@@ -6,7 +6,7 @@ use crate::{
     Beatmap,
 };
 
-use super::{catch_object::CatchObject, slider_state::SliderState, CatchDifficultyAttributes};
+use super::{catch_object::CatchObject, CatchDifficultyAttributes};
 
 const LEGACY_LAST_TICK_OFFSET: f64 = 36.0;
 const BASE_SCORING_DISTANCE: f64 = 100.0;
@@ -18,7 +18,6 @@ pub(crate) struct FruitParams<'a> {
     pub(crate) last_pos: Option<f32>,
     pub(crate) last_time: f64,
     pub(crate) map: &'a Beatmap,
-    pub(crate) slider_state: SliderState<'a>,
     pub(crate) ticks: Vec<(Pos2, f64)>,
     pub(crate) with_hr: bool,
 }
@@ -55,31 +54,29 @@ impl FruitOrJuice {
                 params.last_pos = Some(h.pos.x + control_points[control_points.len() - 1].pos.x);
                 params.last_time = h.start_time;
 
-                // Responsible for timing point values
-                params.slider_state.update(h.start_time);
+                let timing_point = params.map.timing_point_at(h.start_time);
+
+                let difficulty_point = params
+                    .map
+                    .difficulty_point_at(h.start_time)
+                    .unwrap_or_default();
+
+                let vel_factor =
+                    BASE_SCORING_DISTANCE * params.map.slider_mult / timing_point.beat_len;
+                let tick_dist_factor =
+                    BASE_SCORING_DISTANCE * params.map.slider_mult / params.map.tick_rate;
+
+                let vel = vel_factor * difficulty_point.slider_vel;
+
+                let mut tick_dist = tick_dist_factor * difficulty_point.slider_vel;
 
                 let span_count = (*repeats + 1) as f64;
 
-                let mut tick_dist = 100.0 * params.map.slider_mult / params.map.tick_rate;
-
-                if params.map.version >= 8 {
-                    tick_dist /= (100.0 / params.slider_state.slider_velocity)
-                        .max(10.0)
-                        .min(1000.0)
-                        / 100.0;
-                }
-
                 // Build the curve w.r.t. the control points
                 let curve = Curve::new(control_points, *pixel_len, &mut params.curve_bufs);
 
-                let velocity = (BASE_SCORING_DISTANCE
-                    * params.map.slider_mult
-                    * params.slider_state.slider_velocity)
-                    / params.slider_state.beat_len;
-
-                let end_time = h.start_time + span_count * curve.dist() / velocity;
-                let duration = end_time - h.start_time;
-                let span_duration = duration / span_count;
+                let total_duration = span_count * curve.dist() / vel;
+                let span_duration = total_duration / span_count;
 
                 // * A very lenient maximum length of a slider for ticks to be generated.
                 // * This exists for edge cases such as /b/1573664 where the beatmap has
@@ -88,12 +85,13 @@ impl FruitOrJuice {
 
                 let len = curve.dist().min(max_len);
                 tick_dist = tick_dist.clamp(0.0, len);
-                let min_dist_from_end = velocity * 10.0;
+                let min_dist_from_end = vel * 10.0;
 
                 let mut curr_dist = tick_dist;
-                let time_add = duration * tick_dist / (*pixel_len * span_count);
+                let pixel_len = pixel_len.unwrap_or(0.0);
+                let time_add = total_duration * tick_dist / (pixel_len * span_count);
 
-                let target = *pixel_len - tick_dist / 8.0;
+                let target = pixel_len - tick_dist / 8.0;
 
                 let mut slider_objects = vec![(h.pos, h.start_time)];
 
@@ -112,7 +110,7 @@ impl FruitOrJuice {
                     params.attributes.n_tiny_droplets += tiny_droplet_count(
                         h.start_time,
                         time_add,
-                        duration,
+                        total_duration,
                         span_count as usize,
                         &params.ticks,
                     );
@@ -160,7 +158,7 @@ impl FruitOrJuice {
                 // Slider tail
                 let progress = (*repeats % 2 == 0) as u8 as f64;
                 let pos = h.pos + curve.position_at(progress);
-                slider_objects.push((pos, h.start_time + duration));
+                slider_objects.push((pos, h.start_time + total_duration));
 
                 let new_fruits = 2 + (tick_dist > 0.0) as usize * *repeats;
                 params.attributes.n_fruits += new_fruits;

src/catch/gradual_difficulty.rs

@@ -1,10 +1,7 @@
 use std::{iter, slice::Iter};
 
 use crate::{
-    catch::{
-        difficulty_object::DifficultyObject, slider_state::SliderState, SECTION_LENGTH,
-        STAR_SCALING_FACTOR,
-    },
+    catch::{difficulty_object::DifficultyObject, SECTION_LENGTH, STAR_SCALING_FACTOR},
     curve::CurveBuffers,
     parse::{HitObject, Pos2},
     Beatmap, Mods,
@@ -179,7 +176,6 @@ impl<'map> CatchObjectIter<'map> {
             last_pos: None,
             last_time: 0.0,
             map,
-            slider_state: SliderState::new(map),
             ticks: Vec::new(),
             with_hr: mods.hr(),
         };

src/catch/mod.rs

@@ -5,7 +5,6 @@ mod gradual_difficulty;
 mod gradual_performance;
 mod movement;
 mod pp;
-mod slider_state;
 
 use catch_object::CatchObject;
 use difficulty_object::DifficultyObject;
@@ -14,7 +13,6 @@ pub use gradual_difficulty::*;
 pub use gradual_performance::*;
 use movement::Movement;
 pub use pp::*;
-use slider_state::SliderState;
 
 use crate::{catch::fruit_or_juice::FruitParams, curve::CurveBuffers, Beatmap, Mods, OsuStars};
 
@@ -161,7 +159,6 @@ fn calculate_movement(params: CatchStars<'_>) -> (Movement, CatchDifficultyAttri
         last_pos: None,
         last_time: 0.0,
         map,
-        slider_state: SliderState::new(map),
         ticks: Vec::new(), // using the same buffer for all sliders
         with_hr: mods.hr(),
     };

src/catch/slider_state.rs

@@ -1,100 +0,0 @@
-use crate::beatmap::{Beatmap, ControlPoint, ControlPointIter};
-
-#[derive(Clone, Debug)]
-pub(crate) struct SliderState<'p> {
-    control_points: ControlPointIter<'p>,
-    next: Option<ControlPoint>,
-    pub(crate) beat_len: f64,
-    pub(crate) slider_velocity: f64,
-}
-
-impl<'p> SliderState<'p> {
-    #[inline]
-    pub(crate) fn new(map: &'p Beatmap) -> Self {
-        let mut control_points = ControlPointIter::new(map);
-
-        let (beat_len, slider_velocity) = match control_points.next() {
-            Some(ControlPoint::Timing(point)) => (point.beat_len, 1.0),
-            Some(ControlPoint::Difficulty(point)) => (1000.0, point.speed_multiplier),
-            None => (1000.0, 1.0),
-        };
-
-        Self {
-            next: control_points.next(),
-            control_points,
-            beat_len,
-            slider_velocity,
-        }
-    }
-
-    #[inline]
-    pub(crate) fn update(&mut self, time: f64) {
-        while let Some(next) = self.next.as_ref().filter(|n| time >= n.time()) {
-            match next {
-                ControlPoint::Timing(point) => {
-                    self.beat_len = point.beat_len;
-                    self.slider_velocity = 1.0;
-                }
-                ControlPoint::Difficulty(point) => self.slider_velocity = point.speed_multiplier,
-            }
-
-            self.next = self.control_points.next();
-        }
-    }
-}
-
-#[cfg(test)]
-mod test {
-    use crate::beatmap::{Beatmap, DifficultyPoint, TimingPoint};
-
-    use super::SliderState;
-
-    #[test]
-    fn catch_slider_state() {
-        let map = Beatmap {
-            timing_points: vec![
-                TimingPoint {
-                    time: 1.0,
-                    beat_len: 10.0,
-                    kiai: false,
-                },
-                TimingPoint {
-                    time: 3.0,
-                    beat_len: 20.0,
-                    kiai: false,
-                },
-                TimingPoint {
-                    time: 4.0,
-                    beat_len: 30.0,
-                    kiai: false,
-                },
-            ],
-            difficulty_points: vec![
-                DifficultyPoint {
-                    time: 2.0,
-                    speed_multiplier: 15.0,
-                    kiai: false,
-                },
-                DifficultyPoint {
-                    time: 5.0,
-                    speed_multiplier: 45.0,
-                    kiai: false,
-                },
-            ],
-            ..Default::default()
-        };
-
-        let mut state = SliderState::new(&map);
-
-        state.update(2.0);
-        assert!((state.beat_len - 10.0).abs() <= f64::EPSILON);
-
-        state.update(3.0);
-        assert!((state.beat_len - 20.0).abs() <= f64::EPSILON);
-        assert!((state.slider_velocity - 1.0).abs() <= f64::EPSILON);
-
-        state.update(5.0);
-        assert!((state.beat_len - 30.0).abs() <= f64::EPSILON);
-        assert!((state.slider_velocity - 45.0).abs() <= f64::EPSILON);
-    }
-}

src/curve.rs

@@ -1,4 +1,4 @@
-use std::{borrow::Cow, cmp::Ordering, convert::identity, f32::consts::PI, iter};
+use std::{borrow::Cow, cmp::Ordering, convert::identity, f64::consts::PI, iter};
 
 use crate::parse::{PathControlPoint, PathType, Pos2};
 
@@ -58,7 +58,7 @@ pub(crate) struct Curve {
 impl Curve {
     pub(crate) fn new(
         points: &[PathControlPoint],
-        expected_len: f64,
+        expected_len: Option<f64>,
         bufs: &mut CurveBuffers,
     ) -> Self {
         let mut path = Self::calculate_path(points, bufs);
@@ -153,7 +153,7 @@ impl Curve {
     fn calculate_length(
         points: &[PathControlPoint],
         path: &mut Vec<Pos2>,
-        expected_len: f64,
+        expected_len: Option<f64>,
     ) -> Vec<f64> {
         let mut calculated_len = 0.0;
         let mut cumulative_len = Vec::with_capacity(path.len());
@@ -167,7 +167,7 @@ impl Curve {
 
         cumulative_len.extend(length_iter);
 
-        if (expected_len - calculated_len).abs() > f64::EPSILON {
+        if let Some(expected_len) = expected_len.filter(|&len| calculated_len != len) {
             // * In osu-stable, if the last two control points of a slider are equal, extension is not performed
             let condition_opt = points
                 .len()
@@ -490,8 +490,8 @@ impl Curve {
 
         let radius = d_a.length();
 
-        let theta_start = d_a.y.atan2(d_a.x);
-        let mut theta_end = d_c.y.atan2(d_c.x);
+        let theta_start = (d_a.y as f64).atan2(d_a.x as f64);
+        let mut theta_end = (d_c.y as f64).atan2(d_c.x as f64);
 
         while theta_end < theta_start {
             theta_end += 2.0 * PI;
@@ -515,8 +515,8 @@ impl Curve {
         }
 
         Some(CircularArcProperties {
-            theta_start: theta_start as f64,
-            theta_range: theta_range as f64,
+            theta_start,
+            theta_range,
             direction,
             radius,
             centre,

src/gradual.rs

@@ -36,7 +36,7 @@ use crate::{
 ///     // ...
 /// }
 /// ```
-#[derive(Clone, Debug)]
+#[derive(Debug)]
 #[allow(clippy::large_enum_variant)]
 pub enum GradualDifficultyAttributes<'map> {
     /// Gradual osu!catch difficulty attributes.
@@ -268,7 +268,7 @@ impl From<ScoreState> for TaikoScoreState {
 /// // attempting to process further objects will return `None`.
 /// assert!(gradual_perf.process_next_object(state).is_none());
 /// ```
-#[derive(Clone, Debug)]
+#[derive(Debug)]
 #[allow(clippy::large_enum_variant)]
 pub enum GradualPerformanceAttributes<'map> {
     /// Gradual osu!catch performance attributes.

src/lib.rs

@@ -513,3 +513,18 @@ impl From<taiko::TaikoPerformanceAttributes> for PerformanceAttributes {
 
 #[cfg(all(feature = "async_tokio", feature = "async_std"))]
 compile_error!("Only one of the features `async_tokio` and `async_std` should be enabled");
+
+#[cfg(test)]
+mod tests {
+    use crate::{Beatmap, OsuPP};
+
+    #[test]
+    fn custom() {
+        let path = "F:\\osu!\\beatmaps\\2536330.osu";
+        let map = Beatmap::from_path(path).unwrap();
+
+        let attrs = OsuPP::new(&map).calculate();
+
+        println!("{:#?}", attrs);
+    }
+}

src/limited_queue.rs

@@ -70,10 +70,6 @@ impl<T, const N: usize> LimitedQueue<T, N> {
         }
     }
 
-    pub(crate) fn full(&self) -> bool {
-        self.len == N
-    }
-
     pub(crate) fn iter(&self) -> LimitedQueueIter<'_, T> {
         self.queue
             .iter()

src/osu/difficulty_object.rs

@@ -3,248 +3,284 @@ use crate::{
     parse::Pos2,
 };
 
-use super::{OsuObject, ScalingFactor, NORMALIZED_RADIUS};
+use super::{osu_object::NestedObject, OsuObject, ScalingFactor};
 
-const MIN_DELTA_TIME: f64 = 25.0;
-const MAXIMUM_SLIDER_RADIUS: f32 = NORMALIZED_RADIUS * 2.4;
-const ASSUMED_SLIDER_RADIUS: f32 = NORMALIZED_RADIUS * 1.8;
-
-pub(crate) struct DifficultyObject<'h> {
+#[derive(Clone, Debug)]
+pub(crate) struct OsuDifficultyObject<'h> {
+    pub(crate) start_time: f64,
+    pub(crate) delta_time: f64,
     pub(crate) base: &'h OsuObject,
-    pub(crate) clock_rate: f64,
-
-    pub(crate) delta: f64,
     pub(crate) strain_time: f64,
-
-    pub(crate) angle: Option<f64>,
-    pub(crate) jump_dist: f64,
-
-    pub(crate) movement_dist: f64,
-    pub(crate) movement_time: f64,
-
-    pub(crate) travel_dist: f64,
-    pub(crate) travel_time: f64,
+    pub(crate) dists: Distances,
+    pub(crate) idx: usize,
 }
 
-impl<'h> DifficultyObject<'h> {
-    pub(super) fn new(
+impl<'h> OsuDifficultyObject<'h> {
+    pub(crate) const MIN_DELTA_TIME: u32 = 25;
+
+    pub(crate) fn new(
         base: &'h OsuObject,
-        prev: &mut OsuObject,
-        prev_prev: Option<&OsuObject>,
-        scaling_factor: &ScalingFactor,
+        last: &'h OsuObject,
         clock_rate: f64,
+        idx: usize,
+        dists: Distances,
     ) -> Self {
-        let delta = (base.time - prev.time) / clock_rate;
+        let start_time = base.start_time / clock_rate;
+        let delta_time = (base.start_time - last.start_time) / clock_rate;
 
-        // * Capped to 25ms to prevent difficulty calculation breaking from simultaneous objects
-        let strain_time = delta.max(MIN_DELTA_TIME);
+        // * Capped to 25ms to prevent difficulty calculation breaking from simultaneous objects.
+        let strain_time = delta_time.max(Self::MIN_DELTA_TIME as f64);
 
-        // * We don't need to calculate either angle or distances
-        // * when one of the last->curr objects is a spinner
-        let (travel_dist, travel_time, movement_dist, movement_time, jump_dist, angle) =
-            if base.is_spinner() || prev.is_spinner() {
-                (0.0, 0.0, 0.0, 0.0, 0.0, None)
-            } else {
-                let prev_stack_offset = scaling_factor.stack_offset(prev.stack_height);
-
-                // Important to call `Self::compute_slider_cursor_pos` before using `prev.lazy_end_pos`
-                // because the lazy end position is being calculated in that function
-                let (travel_dist, travel_time) = Self::compute_slider_cursor_pos(
-                    prev,
-                    prev_stack_offset,
-                    scaling_factor.raw(),
-                    clock_rate,
-                );
-
-                let prev_cursor_pos = prev.lazy_end_pos(prev_stack_offset);
-
-                let jump_dist =
-                    ((base.pos - prev_cursor_pos) * scaling_factor.adjusted()).length() as f64;
-
-                let angle =
-                    prev_prev
-                        .filter(|prev_prev| !prev_prev.is_spinner())
-                        .map(|prev_prev| {
-                            let prev_prev_cursor_pos = prev_prev
-                                .lazy_end_pos(scaling_factor.stack_offset(prev_prev.stack_height));
-
-                            let v1 = prev_prev_cursor_pos - prev.pos;
-                            let v2 = base.pos - prev_cursor_pos;
-
-                            let dot = (v1.dot(v2)) as f64;
-                            let det = (v1.x * v2.y - v1.y * v2.x) as f64;
-
-                            det.atan2(dot).abs()
-                        });
-
-                let (movement_dist, movement_time) = Self::compute_movement_values(
-                    prev,
-                    base.pos,
-                    jump_dist,
-                    strain_time,
-                    travel_time,
-                    scaling_factor.adjusted(),
-                );
-
-                (
-                    travel_dist,
-                    travel_time,
-                    movement_dist,
-                    movement_time,
-                    jump_dist,
-                    angle,
-                )
-            };
-
-        // ? Common values to debug
-        // println!("travel_dist={} | travel_time={}", travel_dist, travel_time);
+        // TODO: remove
         // println!(
-        //     "movement_dist={} | movement_time={}",
-        //     movement_dist, movement_time
+        //     "[{}] lazy_jump_dist={} | lazy_travel_dist={} | \
+        //     min_jump_dist={} | min_jump_time={} \
+        //     | travel_dist={} | travel_time={} | angle={:?}",
+        //     base.start_time,
+        //     dists.lazy_jump_dist,
+        //     dists.lazy_travel_dist,
+        //     dists.min_jump_dist,
+        //     dists.min_jump_time,
+        //     dists.travel_dist,
+        //     dists.travel_time,
+        //     dists.angle,
         // );
-        // println!(
-        //     "jump_dist={} | strain_time={} | angle={:?}",
-        //     jump_dist, strain_time, angle
-        // );
-        // println!("--");
 
         Self {
+            start_time,
+            delta_time,
             base,
-            clock_rate,
-            delta,
             strain_time,
-            jump_dist,
-            angle,
-            movement_dist,
-            movement_time,
-            travel_dist,
-            travel_time,
+            dists,
+            idx,
         }
     }
 
-    fn compute_slider_cursor_pos(
-        prev: &mut OsuObject,
-        stack_offset: Pos2,
-        scaling_factor: f64,
-        clock_rate: f64,
-    ) -> (f64, f64) {
-        match &mut prev.kind {
-            OsuObjectKind::Circle | OsuObjectKind::Spinner { .. } => (0.0, 0.0),
-            OsuObjectKind::Slider {
-                lazy_end_pos,
-                nested_objects,
-                ..
-            } => {
-                let mut travel_dist = 0.0;
-                let pos = prev.pos - stack_offset; // stack offset is ignored everywhere
-                let mut curr_cursor_pos = pos;
-
-                let last_idx = nested_objects.len() - 1;
-
-                for (i, nested) in nested_objects.iter_mut().enumerate() {
-                    let mut curr_movement = nested.pos - curr_cursor_pos;
-                    let mut curr_movement_len = scaling_factor * curr_movement.length() as f64;
-
-                    // * Amount of movement required so that the cursor position needs to be updated.
-                    let mut required_movement = ASSUMED_SLIDER_RADIUS as f64;
-
-                    if i == last_idx {
-                        // * The end of a slider has special aim rules due
-                        // * to the relaxed time constraint on position.
-                        // * There is both a lazy end position as well as the actual end slider position.
-                        // * We assume the player takes the simpler movement.
-                        // * For sliders that are circular, the lazy end position
-                        // * may actually be farther away than the sliders true end.
-                        // * This code is designed to prevent buffing situations
-                        // * where lazy end is actually a less efficient movement.
-                        let lazy_movement = *lazy_end_pos - curr_cursor_pos;
-
-                        if lazy_movement.length() < curr_movement.length() {
-                            curr_movement = lazy_movement;
-                        }
-
-                        curr_movement_len = scaling_factor * curr_movement.length() as f64;
-                    } else if let NestedObjectKind::Repeat = nested.kind {
-                        // * For a slider repeat, assume a tighter movement
-                        // * threshold to better assess repeat sliders.
-                        required_movement = NORMALIZED_RADIUS as f64;
-                    }
-
-                    if curr_movement_len > required_movement {
-                        // * this finds the positional delta from the required
-                        // * radius and the current position, and updates the
-                        // * currCursorPosition accordingly, as well as rewarding distance.
-                        curr_cursor_pos += curr_movement
-                            * ((curr_movement_len - required_movement) / curr_movement_len) as f32;
-
-                        curr_movement_len *=
-                            (curr_movement_len - required_movement) / curr_movement_len;
-
-                        travel_dist += curr_movement_len;
-                    }
-
-                    if i == last_idx {
-                        *lazy_end_pos = curr_cursor_pos;
-                    }
-                }
-
-                let repeats = nested_objects
-                    .iter()
-                    .filter(|nested| matches!(nested.kind, NestedObjectKind::Repeat))
-                    .count();
-
-                // * Bonus for repeat sliders until a better per
-                // * nested object strain system can be achieved.
-                travel_dist *= (1.0 + repeats as f64 / 2.5).powf(1.0 / 2.5);
-                let prev_time = prev.time;
-
-                let lazy_travel_time = nested_objects
-                    .last()
-                    .map_or(0.0, |nested| nested.time - prev_time);
-
-                let travel_time = MIN_DELTA_TIME.max(lazy_travel_time / clock_rate);
-
-                (travel_dist, travel_time)
-            }
+    pub(crate) fn opacity_at(&self, time: f64, hidden: bool) -> f64 {
+        if time > self.base.start_time {
+            // * Consider a hitobject as being invisible when its start time is passed.
+            // * In reality the hitobject will be visible beyond its start time up until its hittable window has passed,
+            // * but this is an approximation and such a case is unlikely to be hit where this function is used.
+            return 0.0;
         }
-    }
 
-    fn compute_movement_values(
-        prev: &OsuObject,
-        base_pos: Pos2,
-        jump_dist: f64,
-        strain_time: f64,
-        travel_time: f64,
-        scaling_factor: f32,
-    ) -> (f64, f64) {
-        match &prev.kind {
-            OsuObjectKind::Circle | OsuObjectKind::Spinner { .. } => (jump_dist, strain_time),
-            OsuObjectKind::Slider { end_pos, .. } => {
-                let movement_time = MIN_DELTA_TIME.max(strain_time - travel_time);
+        let fade_in_start_time = self.base.start_time - self.base.time_preempt;
+        let fade_in_duration = self.base.time_fade_in;
 
-                // * Jump distance from the slider tail to the next object,
-                // * as opposed to the lazy position of JumpDistance.
-                let tail_jump_dist = (*end_pos - base_pos).length() * scaling_factor;
+        if hidden {
+            // * Taken from OsuModHidden.
+            let fade_out_start_time =
+                self.base.start_time - self.base.time_preempt + self.base.time_fade_in;
+            const FADE_OUT_DURATION_MULTIPLIER: f64 = 0.3;
+            let fade_out_duration = self.base.time_preempt * FADE_OUT_DURATION_MULTIPLIER;
 
-                // * For hitobjects which continue in the direction of the slider,
-                // * the player will normally follow through the slider,
-                // * such that they're not jumping from the lazy position but
-                // * rather from very close to (or the end of) the slider.
-                // * In such cases, a leniency is applied by also considering the
-                // * jump distance from the tail of the slider,
-                // * and taking the minimum jump distance.
-                // * Additional distance is removed based on position of jump
-                // * relative to slider follow circle radius.
-                // * JumpDistance is the leniency distance beyond the assumed_slider_radius.
-                // * tailJumpDistance is maximum_slider_radius since
-                // * the full distance of radial leniency is still possible.
-                let movement_dist = (jump_dist
-                    - (MAXIMUM_SLIDER_RADIUS - ASSUMED_SLIDER_RADIUS) as f64)
-                    .min((tail_jump_dist - MAXIMUM_SLIDER_RADIUS) as f64)
-                    .max(0.0);
-
-                (movement_dist, movement_time)
-            }
+            (((time - fade_in_start_time) / fade_in_duration).clamp(0.0, 1.0))
+                .min(1.0 - ((time - fade_out_start_time) / fade_out_duration).clamp(0.0, 1.0))
+        } else {
+            ((time - fade_in_start_time) / fade_in_duration).clamp(0.0, 1.0)
+        }
+    }
+}
+
+#[derive(Clone, Debug, Default)]
+pub(crate) struct Distances {
+    pub(crate) lazy_jump_dist: f64,
+    pub(crate) lazy_travel_dist: f32,
+    pub(crate) min_jump_dist: f64,
+    pub(crate) min_jump_time: f64,
+    pub(crate) travel_dist: f64,
+    pub(crate) travel_time: f64,
+    pub(crate) angle: Option<f64>,
+}
+
+impl Distances {
+    pub(crate) const NORMALISED_RADIUS: f32 = 50.0;
+
+    const MAXIMUM_SLIDER_RADIUS: f32 = Self::NORMALISED_RADIUS * 2.4;
+    const ASSUMED_SLIDER_RADIUS: f32 = Self::NORMALISED_RADIUS * 1.8;
+
+    pub(crate) fn new(
+        base: &mut OsuObject,
+        last: &OsuObject,
+        last_last: Option<&OsuObject>,
+        clock_rate: f64,
+        strain_time: f64,
+        scaling_factor_: &ScalingFactor,
+    ) -> Self {
+        let mut this = if let OsuObjectKind::Slider {
+            lazy_end_pos,
+            lazy_travel_time,
+            nested_objects,
+            ..
+        } = &mut base.kind
+        {
+            let lazy_travel_dist = Self::compute_slider_cursor_pos(
+                base.pos,
+                base.start_time,
+                lazy_end_pos,
+                lazy_travel_time,
+                nested_objects,
+                scaling_factor_,
+            );
+
+            let repeat_count = nested_objects.iter().fold(0, |repeats, nested| {
+                repeats + matches!(nested.kind, NestedObjectKind::Repeat) as usize
+            });
+
+            Self {
+                // * Bonus for repeat sliders until a better per nested object strain system can be achieved.
+                travel_dist: (lazy_travel_dist
+                    * (1.0 + repeat_count as f64 / 2.5).powf(1.0 / 2.5) as f32)
+                    as f64,
+                travel_time: lazy_travel_time.max(OsuDifficultyObject::MIN_DELTA_TIME as f64),
+                lazy_travel_dist,
+                ..Default::default()
+            }
+        } else {
+            Self::default()
+        };
+
+        // * We don't need to calculate either angle or distance when
+        // * one of the last->curr objects is a spinner
+        if base.is_spinner() || last.is_spinner() {
+            return this;
+        }
+
+        // * We will scale distances by this factor, so we can assume a uniform CircleSize among beatmaps.
+        let scaling_factor = scaling_factor_.factor;
+
+        let last_cursor_pos = Self::get_end_cursor_pos(last, scaling_factor_);
+
+        this.lazy_jump_dist =
+            (base.pos * scaling_factor - last_cursor_pos * scaling_factor).length() as f64;
+        this.min_jump_time = strain_time;
+        this.min_jump_dist = this.lazy_jump_dist;
+
+        if let OsuObjectKind::Slider {
+            end_pos,
+            lazy_travel_time,
+            ..
+        } = &last.kind
+        {
+            let last_travel_dist =
+                (lazy_travel_time / clock_rate).max(OsuDifficultyObject::MIN_DELTA_TIME as f64);
+            this.min_jump_time =
+                (strain_time - last_travel_dist).max(OsuDifficultyObject::MIN_DELTA_TIME as f64);
+
+            // * There are two types of slider-to-object patterns to consider in order
+            // * to better approximate the real movement a player will take to jump between the hitobjects.
+            // *
+            // * 1. The anti-flow pattern, where players cut the slider short in order to move to the next hitobject.
+            // *
+            // *     <======o==>  ← slider
+            // *            |     ← most natural jump path
+            // *            o     ← a follow-up hitcircle
+            // *
+            // * In this case the most natural jump path is approximated by LazyJumpDistance.
+            // *
+            // * 2. The flow pattern, where players follow through the slider to its
+            // * visual extent into the next hitobject.
+            // *
+            // *     <======o==>---o
+            // *                 ↑
+            // *       most natural jump path
+            // *
+            // * In this case the most natural jump path is better approximated by a new distance
+            // * called "tailJumpDistance" - the distance between the slider's tail and the next hitobject.
+            // *
+            // * Thus, the player is assumed to jump the minimum of these two distances in all cases.
+
+            let tail_jump_dist = (*end_pos - base.pos).length() * scaling_factor;
+
+            this.min_jump_dist = ((this.lazy_jump_dist
+                - (Self::MAXIMUM_SLIDER_RADIUS - Self::ASSUMED_SLIDER_RADIUS) as f64)
+                .min((tail_jump_dist - Self::MAXIMUM_SLIDER_RADIUS) as f64))
+            .max(0.0);
+        }
+
+        if let Some(last_last) = last_last.filter(|obj| !obj.is_spinner()) {
+            let last_last_cursor_pos = Self::get_end_cursor_pos(last_last, scaling_factor_);
+
+            let v1 = last_last_cursor_pos - last.pos;
+            let v2 = base.pos - last_cursor_pos;
+
+            let dot = v1.dot(v2) as f64;
+            let det = (v1.x * v2.y - v1.y * v2.x) as f64;
+
+            this.angle = Some(det.atan2(dot).abs());
+        }
+
+        this
+    }
+
+    pub(crate) fn compute_slider_cursor_pos(
+        stacked_pos: Pos2,
+        start_time: f64,
+        lazy_end_pos: &mut Pos2,
+        lazy_travel_time: &mut f64,
+        nested_objects: &[NestedObject],
+        scaling_factor_: &ScalingFactor,
+    ) -> f32 {
+        let mut curr_cursor_pos = stacked_pos;
+        let scaling_factor = Self::NORMALISED_RADIUS as f64 / scaling_factor_.radius as f64;
+
+        let mut lazy_travel_dist: f32 = 0.0;
+
+        for (curr_movement_obj, i) in nested_objects.iter().zip(1..) {
+            let mut curr_movement = curr_movement_obj.pos - curr_cursor_pos;
+            let mut curr_movement_len = scaling_factor * curr_movement.length() as f64;
+
+            // * Amount of movement required so that the cursor position needs to be updated.
+            let mut required_movement = Self::ASSUMED_SLIDER_RADIUS as f64;
+
+            if i == nested_objects.len() {
+                // * The end of a slider has special aim rules due
+                // * to the relaxed time constraint on position.
+                // * There is both a lazy end position as well as the actual end slider position.
+                // * We assume the player takes the simpler movement.
+                // * For sliders that are circular, the lazy end position
+                // * may actually be farther away than the sliders true end.
+                // * This code is designed to prevent buffing situations
+                // * where lazy end is actually a less efficient movement.
+                let lazy_movement = *lazy_end_pos - curr_cursor_pos;
+
+                if lazy_movement.length() < curr_movement.length() {
+                    curr_movement = lazy_movement;
+                }
+
+                curr_movement_len = scaling_factor * curr_movement.length() as f64;
+            } else if let NestedObjectKind::Repeat = curr_movement_obj.kind {
+                // * For a slider repeat, assume a tighter movement threshold to better assess repeat sliders.
+                required_movement = Self::NORMALISED_RADIUS as f64;
+            }
+
+            if curr_movement_len > required_movement {
+                // * this finds the positional delta from the required radius and the current position, and updates the currCursorPosition accordingly, as well as rewarding distance.
+                curr_cursor_pos += curr_movement
+                    * ((curr_movement_len - required_movement) / curr_movement_len) as f32;
+                curr_movement_len *= (curr_movement_len - required_movement) / curr_movement_len;
+                lazy_travel_dist += curr_movement_len as f32;
+            }
+
+            if i == nested_objects.len() {
+                *lazy_end_pos = curr_cursor_pos;
+            }
+        }
+
+        *lazy_travel_time = nested_objects
+            .last()
+            .map_or(0.0, |nested| nested.start_time - start_time);
+
+        lazy_travel_dist
+    }
+
+    fn get_end_cursor_pos(hit_object: &OsuObject, scaling_factor: &ScalingFactor) -> Pos2 {
+        if hit_object.is_slider() {
+            let stack_offset = scaling_factor.stack_offset(hit_object.stack_height);
+
+            hit_object.lazy_end_pos(stack_offset)
+        } else {
+            hit_object.pos
         }
     }
 }

src/osu/gradual_difficulty.rs

@@ -1,16 +1,19 @@
-use std::{iter, mem, vec::IntoIter};
-
-use crate::{
-    curve::CurveBuffers, osu::difficulty_object::DifficultyObject, parse::Pos2, Beatmap, Mods,
+use std::{
+    fmt::{Debug, Formatter, Result as FmtResult},
+    mem,
+    vec::IntoIter,
 };
 
+use crate::{curve::CurveBuffers, Beatmap, Mods};
+
 use super::{
-    calculate_star_rating, old_stacking,
+    create_skills,
+    difficulty_object::{Distances, OsuDifficultyObject},
+    old_stacking,
     osu_object::{ObjectParameters, OsuObject, OsuObjectKind},
     scaling_factor::ScalingFactor,
-    skill::{Skill, Skills},
-    slider_state::SliderState,
-    stacking, OsuDifficultyAttributes, DIFFICULTY_MULTIPLIER, SECTION_LEN,
+    skills::{Aim, Flashlight, Skill, Speed},
+    stacking, OsuDifficultyAttributes, DIFFICULTY_MULTIPLIER, PERFORMANCE_BASE_MULTIPLIER,
 };
 
 /// Gradually calculate the difficulty attributes of an osu!standard map.
@@ -43,39 +46,47 @@ use super::{
 ///     // ...
 /// }
 /// ```
-#[derive(Clone, Debug)]
 pub struct OsuGradualDifficultyAttributes {
     pub(crate) idx: usize,
+    mods: u32,
     attributes: OsuDifficultyAttributes,
-    clock_rate: f64,
-    hit_objects: OsuObjectIter,
-    skills: Skills,
-    prev_prev: Option<OsuObject>,
-    prev: OsuObject,
-    curr_section_end: f64,
-    strain_peak_buf: Vec<f64>,
+    hit_objects: Vec<OsuObject>,
+    diff_objects: Vec<OsuDifficultyObject<'static>>,
+    skills: [Box<dyn Skill>; 4],
+    hit_window: f64,
+}
+
+impl Debug for OsuGradualDifficultyAttributes {
+    fn fmt(&self, f: &mut Formatter<'_>) -> FmtResult {
+        f.debug_struct("OsuGradualDifficultyAttributes")
+            .field("idx", &self.idx)
+            .field("attributes", &self.attributes)
+            .field("hit_objects", &self.hit_objects)
+            .field("skills", &"<cannot be displayed>")
+            .finish()
+    }
 }
 
 impl OsuGradualDifficultyAttributes {
     /// Create a new difficulty attributes iterator for osu!standard maps.
     pub fn new(map: &Beatmap, mods: u32) -> Self {
-        let map_attributes = map.attributes().mods(mods).build();
-        let hit_window = map_attributes.hit_windows.od;
-        let time_preempt = map_attributes.hit_windows.ar;
+        let clock_rate = mods.clock_rate();
+        let map_attrs = map.attributes().mods(mods).build();
+        let scaling_factor = ScalingFactor::new(map_attrs.cs);
         let hr = mods.hr();
-        let scaling_factor = ScalingFactor::new(map_attributes.cs);
+        let time_preempt = map_attrs.hit_windows.ar;
+        let hit_window = 2.0 * map_attrs.hit_windows.od;
 
-        let mut attributes = OsuDifficultyAttributes {
-            ar: map_attributes.ar,
-            hp: map_attributes.hp,
-            od: map_attributes.od,
+        let mut attrs = OsuDifficultyAttributes {
+            ar: map_attrs.ar,
+            hp: map_attrs.hp,
+            od: map_attrs.od,
             ..Default::default()
         };
 
         let mut params = ObjectParameters {
             map,
-            attributes: &mut attributes,
-            slider_state: SliderState::new(map),
+            attributes: &mut attrs,
             ticks: Vec::new(),
             curve_bufs: CurveBuffers::default(),
         };
@@ -88,10 +99,10 @@ impl OsuGradualDifficultyAttributes {
         let mut hit_objects = Vec::with_capacity(map.hit_objects.len());
         hit_objects.extend(hit_objects_iter);
 
-        attributes.n_circles = 0;
-        attributes.n_sliders = 0;
-        attributes.n_spinners = 0;
-        attributes.max_combo = 0;
+        attrs.n_circles = 0;
+        attrs.n_sliders = 0;
+        attrs.n_spinners = 0;
+        attrs.max_combo = 0;
 
         let stack_threshold = time_preempt * map.stack_leniency as f64;
 
@@ -101,162 +112,200 @@ impl OsuGradualDifficultyAttributes {
             old_stacking(&mut hit_objects, stack_threshold);
         }
 
-        let skills = Skills::new(hit_window, mods.rx(), scaling_factor.radius(), mods.fl());
+        let mut hit_objects_iter = hit_objects.iter_mut().map(|h| {
+            let stack_offset = scaling_factor.stack_offset(h.stack_height);
+            h.pos += stack_offset;
 
-        let hit_objects = OsuObjectIter {
-            hit_objects: hit_objects.into_iter(),
-            scaling_factor,
+            h
+        });
+
+        let skills = create_skills(mods, scaling_factor.radius);
+
+        let last = match hit_objects_iter.next() {
+            Some(prev) => prev,
+            None => {
+                return Self {
+                    idx: 0,
+                    mods,
+                    attributes: attrs,
+                    hit_objects: Vec::new(),
+                    diff_objects: Vec::new(),
+                    skills,
+                    hit_window,
+                }
+            }
         };
 
-        let prev_prev = None;
+        let mut last_last = None;
 
-        let prev = OsuObject {
-            time: 0.0,
-            pos: Pos2::zero(),
-            stack_height: 0.0,
-            kind: OsuObjectKind::Circle,
-        };
+        // Prepare `lazy_travel_dist` and `lazy_end_pos` for `last` manually
+        if let OsuObjectKind::Slider {
+            lazy_travel_time,
+            lazy_end_pos,
+            nested_objects,
+            ..
+        } = &mut last.kind
+        {
+            Distances::compute_slider_cursor_pos(
+                last.pos,
+                last.start_time,
+                lazy_end_pos,
+                lazy_travel_time,
+                nested_objects,
+                &scaling_factor,
+            );
+        }
+
+        let mut last = &*last;
+        let mut diff_objects = Vec::with_capacity(map.hit_objects.len().saturating_sub(2));
+
+        for (i, curr) in hit_objects_iter.enumerate() {
+            let delta_time = (curr.start_time - last.start_time) / clock_rate;
+
+            // * Capped to 25ms to prevent difficulty calculation breaking from simultaneous objects.
+            let strain_time = delta_time.max(OsuDifficultyObject::MIN_DELTA_TIME as f64);
+
+            let dists = Distances::new(
+                curr,
+                last,
+                last_last,
+                clock_rate,
+                strain_time,
+                &scaling_factor,
+            );
+
+            let diff_obj = OsuDifficultyObject::new(curr, last, clock_rate, i, dists);
+            diff_objects.push(diff_obj);
+
+            last_last = Some(last);
+            last = &*curr;
+        }
 
         Self {
             idx: 0,
-            attributes,
-            clock_rate: map_attributes.clock_rate,
+            mods,
+            attributes: attrs,
+            diff_objects: extend_lifetime(diff_objects),
             hit_objects,
             skills,
-            curr_section_end: 0.0,
-            prev_prev,
-            prev,
-            strain_peak_buf: Vec::new(),
+            hit_window,
         }
     }
 }
 
+fn extend_lifetime(
+    diff_objects: Vec<OsuDifficultyObject<'_>>,
+) -> Vec<OsuDifficultyObject<'static>> {
+    // SAFETY: Owned values of the references will be contained
+    // in the same struct and hence live just as long as this vec.
+    unsafe { mem::transmute(diff_objects) }
+}
+
 impl Iterator for OsuGradualDifficultyAttributes {
     type Item = OsuDifficultyAttributes;
 
     fn next(&mut self) -> Option<Self::Item> {
-        let curr = self.hit_objects.next()?;
-        self.attributes.max_combo += 1;
-
-        match &curr.kind {
-            OsuObjectKind::Circle => self.attributes.n_circles += 1,
-            OsuObjectKind::Slider { nested_objects, .. } => {
-                self.attributes.max_combo += nested_objects.len();
-                self.attributes.n_sliders += 1
-            }
-            OsuObjectKind::Spinner { .. } => self.attributes.n_spinners += 1,
-        };
-
+        let curr = self.diff_objects.get(self.idx)?;
         self.idx += 1;
 
-        if self.idx == 1 {
-            self.prev = curr;
-            self.curr_section_end =
-                (self.prev.time / self.clock_rate / SECTION_LEN).ceil() * SECTION_LEN;
-
-            return Some(self.attributes.clone());
+        for skill in self.skills.iter_mut() {
+            skill.process(curr, &self.diff_objects, self.hit_window);
         }
 
-        let h = DifficultyObject::new(
-            &curr,
-            &mut self.prev,
-            self.prev_prev.as_ref(),
-            &self.hit_objects.scaling_factor,
-            self.clock_rate,
-        );
+        let mut attrs = self.attributes.clone();
 
-        let base_time = h.base.time / self.clock_rate;
+        attrs.max_combo += 1;
 
-        if self.idx == 2 {
-            while base_time > self.curr_section_end {
-                self.skills.start_new_section_from(self.curr_section_end);
-                self.curr_section_end += SECTION_LEN;
-            }
-        } else {
-            while base_time > self.curr_section_end {
-                self.skills
-                    .save_peak_and_start_new_section(self.curr_section_end);
-                self.curr_section_end += SECTION_LEN;
+        match &curr.base.kind {
+            OsuObjectKind::Circle => attrs.n_circles += 1,
+            OsuObjectKind::Slider { nested_objects, .. } => {
+                attrs.n_sliders += 1;
+                attrs.max_combo += nested_objects.len();
             }
+            OsuObjectKind::Spinner { .. } => attrs.n_spinners += 1,
         }
 
-        self.skills.process(&h);
-        self.prev_prev = Some(mem::replace(&mut self.prev, curr));
+        let [aim, aim_no_sliders, speed, flashlight] = &self.skills;
 
-        let missing = self.skills.aim().strain_peaks.len() + 1 - self.strain_peak_buf.len();
-        self.strain_peak_buf.extend(iter::repeat(0.0).take(missing));
+        let mut aim = aim.as_any().downcast_ref::<Aim>().unwrap().clone();
 
-        let aim_rating = {
-            let aim = self.skills.aim();
-            self.strain_peak_buf[..aim.strain_peaks.len()].copy_from_slice(&aim.strain_peaks);
+        let mut aim_no_sliders = aim_no_sliders
+            .as_any()
+            .downcast_ref::<Aim>()
+            .unwrap()
+            .clone();
 
-            if let Some(last) = self.strain_peak_buf.last_mut() {
-                *last = aim.curr_section_peak;
-            }
+        let mut aim_rating = aim.difficulty_value().sqrt() * DIFFICULTY_MULTIPLIER;
+        let aim_rating_no_sliders =
+            aim_no_sliders.difficulty_value().sqrt() * DIFFICULTY_MULTIPLIER;
 
-            Skill::difficulty_value(&mut self.strain_peak_buf, aim).sqrt() * DIFFICULTY_MULTIPLIER
-        };
+        let mut speed = speed.as_any().downcast_ref::<Speed>().unwrap().clone();
+        let speed_notes = speed.relevant_note_count();
+        let mut speed_rating = speed.difficulty_value().sqrt() * DIFFICULTY_MULTIPLIER;
+
+        let mut flashlight = flashlight
+            .as_any()
+            .downcast_ref::<Flashlight>()
+            .unwrap()
+            .clone();
+
+        let mut flashlight_rating = flashlight.difficulty_value().sqrt() * DIFFICULTY_MULTIPLIER;
 
         let slider_factor = if aim_rating > 0.0 {
-            let aim_no_sliders = self.skills.aim_no_sliders();
-            self.strain_peak_buf[..aim_no_sliders.strain_peaks.len()]
-                .copy_from_slice(&aim_no_sliders.strain_peaks);
-
-            if let Some(last) = self.strain_peak_buf.last_mut() {
-                *last = aim_no_sliders.curr_section_peak;
-            }
-
-            let aim_rating_no_sliders =
-                Skill::difficulty_value(&mut self.strain_peak_buf, aim_no_sliders).sqrt()
-                    * DIFFICULTY_MULTIPLIER;
-
             aim_rating_no_sliders / aim_rating
         } else {
             1.0
         };
 
-        let (speed, flashlight) = self.skills.speed_flashlight();
+        if self.mods.td() {
+            aim_rating = aim_rating.powf(0.8);
+            flashlight_rating = flashlight_rating.powf(0.8);
+        }
 
-        let speed_rating = if let Some(speed) = speed {
-            self.strain_peak_buf[..speed.strain_peaks.len()].copy_from_slice(&speed.strain_peaks);
+        if self.mods.rx() {
+            aim_rating *= 0.9;
+            speed_rating = 0.0;
+            flashlight_rating *= 0.7;
+        }
 
-            if let Some(last) = self.strain_peak_buf.last_mut() {
-                *last = speed.curr_section_peak;
-            }
+        let base_aim_performance = (5.0 * (aim_rating / 0.0675).max(1.0) - 4.0).powi(3) / 100_000.0;
+        let base_speed_performance =
+            (5.0 * (speed_rating / 0.0675).max(1.0) - 4.0).powi(3) / 100_000.0;
 
-            Skill::difficulty_value(&mut self.strain_peak_buf, speed).sqrt() * DIFFICULTY_MULTIPLIER
+        let base_flashlight_performance = if self.mods.fl() {
+            flashlight_rating * flashlight_rating * 25.0
         } else {
             0.0
         };
 
-        let flashlight_rating = if let Some(flashlight) = flashlight {
-            self.strain_peak_buf[..flashlight.strain_peaks.len()]
-                .copy_from_slice(&flashlight.strain_peaks);
+        let base_performance = ((base_aim_performance).powf(1.1)
+            + (base_speed_performance).powf(1.1)
+            + (base_flashlight_performance).powf(1.1))
+        .powf(1.0 / 1.1);
 
-            if let Some(last) = self.strain_peak_buf.last_mut() {
-                *last = flashlight.curr_section_peak;
-            }
-
-            Skill::difficulty_value(&mut self.strain_peak_buf, flashlight).sqrt()
-                * DIFFICULTY_MULTIPLIER
+        let star_rating = if base_performance > 0.00001 {
+            PERFORMANCE_BASE_MULTIPLIER.cbrt()
+                * 0.027
+                * ((100_000.0 / 2.0_f64.powf(1.0 / 1.1) * base_performance).cbrt() + 4.0)
         } else {
             0.0
         };
 
-        let star_rating = calculate_star_rating(aim_rating, speed_rating, flashlight_rating);
+        attrs.aim = aim_rating;
+        attrs.speed = speed_rating;
+        attrs.flashlight = flashlight_rating;
+        attrs.slider_factor = slider_factor;
+        attrs.stars = star_rating;
+        attrs.speed_note_count = speed_notes;
 
-        self.attributes.aim_strain = aim_rating;
-        self.attributes.speed_strain = speed_rating;
-        self.attributes.flashlight_rating = flashlight_rating;
-        self.attributes.slider_factor = slider_factor;
-        self.attributes.stars = star_rating;
-
-        Some(self.attributes.clone())
+        Some(attrs)
     }
 
     #[inline]
     fn size_hint(&self) -> (usize, Option<usize>) {
-        self.hit_objects.size_hint()
+        let len = self.hit_objects.len() - self.idx;
+
+        (len, Some(len))
     }
 }
 

src/osu/gradual_performance.rs

@@ -114,7 +114,7 @@ impl OsuScoreState {
 /// // attempting to process further objects will return `None`.
 /// assert!(gradual_perf.process_next_object(state).is_none());
 /// ```
-#[derive(Clone, Debug)]
+#[derive(Debug)]
 pub struct OsuGradualPerformanceAttributes<'map> {
     difficulty: OsuGradualDifficultyAttributes,
     performance: OsuPP<'map>,

src/osu/mod.rs

@@ -4,30 +4,26 @@ mod gradual_performance;
 mod osu_object;
 mod pp;
 mod scaling_factor;
-mod skill;
-mod skill_kind;
-mod slider_state;
-
-use std::mem;
-
-use difficulty_object::DifficultyObject;
-pub use gradual_difficulty::*;
-pub use gradual_performance::*;
-use osu_object::{ObjectParameters, OsuObject};
-pub use pp::*;
-use scaling_factor::ScalingFactor;
-use skill::Skill;
-use skill_kind::SkillKind;
-use slider_state::SliderState;
+mod skills;
 
 use crate::{curve::CurveBuffers, AnyStars, Beatmap, GameMode, Mods};
 
-use self::skill::Skills;
+use self::{
+    difficulty_object::{Distances, OsuDifficultyObject},
+    osu_object::{ObjectParameters, OsuObject, OsuObjectKind},
+    scaling_factor::ScalingFactor,
+    skills::{Aim, Flashlight, Skill, Speed},
+};
+
+pub use self::{gradual_difficulty::*, gradual_performance::*, pp::*};
 
 const SECTION_LEN: f64 = 400.0;
 const DIFFICULTY_MULTIPLIER: f64 = 0.0675;
-const NORMALIZED_RADIUS: f32 = 50.0; // * diameter of 100; easier mental maths.
+// * Change radius to 50 to make 100 the diameter. Easier for mental maths.
+const NORMALIZED_RADIUS: f32 = 50.0;
 const STACK_DISTANCE: f32 = 3.0;
+// * This is being adjusted to keep the final pp value scaled around what it used to be when changing things.
+const PERFORMANCE_BASE_MULTIPLIER: f64 = 1.14;
 
 /// Difficulty calculator on osu!standard maps.
 ///
@@ -113,60 +109,76 @@ impl<'map> OsuStars<'map> {
     /// Calculate all difficulty related values, including stars.
     #[inline]
     pub fn calculate(self) -> OsuDifficultyAttributes {
-        let (mut skills, mut attributes) = calculate_skills(self);
+        let mods = self.mods;
 
-        let aim_rating = {
-            let aim = skills.aim();
-            let mut aim_strains = mem::take(&mut aim.strain_peaks);
+        let (skills, mut attrs) = calculate_skills(self);
 
-            Skill::difficulty_value(&mut aim_strains, aim).sqrt() * DIFFICULTY_MULTIPLIER
-        };
+        let [mut aim, mut aim_no_sliders, mut speed, mut flashlight] = skills;
+
+        let mut aim_rating = aim.difficulty_value().sqrt() * DIFFICULTY_MULTIPLIER;
+        let aim_rating_no_sliders =
+            aim_no_sliders.difficulty_value().sqrt() * DIFFICULTY_MULTIPLIER;
+
+        let (mut speed_rating, speed_notes) =
+            if let Some(speed) = speed.as_any_mut().downcast_mut::<Speed>() {
+                let notes = speed.relevant_note_count();
+                let rating = speed.difficulty_value().sqrt() * DIFFICULTY_MULTIPLIER;
+
+                (rating, notes)
+            } else {
+                unreachable!()
+            };
+
+        let mut flashlight_rating = flashlight.difficulty_value().sqrt() * DIFFICULTY_MULTIPLIER;
 
         let slider_factor = if aim_rating > 0.0 {
-            let aim_no_sliders = skills.aim_no_sliders();
-
-            let mut aim_strains_no_sliders = mem::take(&mut aim_no_sliders.strain_peaks);
-            let aim_rating_no_sliders =
-                Skill::difficulty_value(&mut aim_strains_no_sliders, aim_no_sliders).sqrt()
-                    * DIFFICULTY_MULTIPLIER;
-
             aim_rating_no_sliders / aim_rating
         } else {
             1.0
         };
 
-        let (speed, flashlight) = skills.speed_flashlight();
+        if mods.td() {
+            aim_rating = aim_rating.powf(0.8);
+            flashlight_rating = flashlight_rating.powf(0.8);
+        }
 
-        let speed_rating = if let Some(speed) = speed {
-            let mut speed_strains = mem::take(&mut speed.strain_peaks);
+        if mods.rx() {
+            aim_rating *= 0.9;
+            speed_rating = 0.0;
+            flashlight_rating *= 0.7;
+        }
 
-            Skill::difficulty_value(&mut speed_strains, speed).sqrt() * DIFFICULTY_MULTIPLIER
+        let base_aim_performance = (5.0 * (aim_rating / 0.0675).max(1.0) - 4.0).powi(3) / 100_000.0;
+        let base_speed_performance =
+            (5.0 * (speed_rating / 0.0675).max(1.0) - 4.0).powi(3) / 100_000.0;
+
+        let base_flashlight_performance = if mods.fl() {
+            flashlight_rating * flashlight_rating * 25.0
         } else {
             0.0
         };
 
-        let flashlight_rating = if let Some(flashlight) = flashlight {
-            let mut flashlight_strains = mem::take(&mut flashlight.strain_peaks);
+        let base_performance = ((base_aim_performance).powf(1.1)
+            + (base_speed_performance).powf(1.1)
+            + (base_flashlight_performance).powf(1.1))
+        .powf(1.0 / 1.1);
 
-            Skill::difficulty_value(&mut flashlight_strains, flashlight).sqrt()
-                * DIFFICULTY_MULTIPLIER
+        let star_rating = if base_performance > 0.00001 {
+            PERFORMANCE_BASE_MULTIPLIER.cbrt()
+                * 0.027
+                * ((100_000.0 / 2.0_f64.powf(1.0 / 1.1) * base_performance).cbrt() + 4.0)
         } else {
             0.0
         };
 
-        let star_rating = if attributes.max_combo == 0 {
-            0.0
-        } else {
-            calculate_star_rating(aim_rating, speed_rating, flashlight_rating)
-        };
+        attrs.aim = aim_rating;
+        attrs.speed = speed_rating;
+        attrs.flashlight = flashlight_rating;
+        attrs.slider_factor = slider_factor;
+        attrs.stars = star_rating;
+        attrs.speed_note_count = speed_notes;
 
-        attributes.aim_strain = aim_rating;
-        attributes.speed_strain = speed_rating;
-        attributes.flashlight_rating = flashlight_rating;
-        attributes.slider_factor = slider_factor;
-        attributes.stars = star_rating;
-
-        attributes
+        attrs
     }
 
     /// Calculate the skill strains.
@@ -175,32 +187,21 @@ impl<'map> OsuStars<'map> {
     #[inline]
     pub fn strains(self) -> OsuStrains {
         let clock_rate = self.clock_rate.unwrap_or_else(|| self.mods.clock_rate());
-        let (mut skills, _) = calculate_skills(self);
+        let (skills, _) = calculate_skills(self);
 
-        let len = skills.aim().strain_peaks.len();
-        let (speed, flashlight) = skills.speed_flashlight();
-
-        let speed = speed.map_or_else(
-            || vec![0.0; len],
-            |skill| mem::take(&mut skill.strain_peaks),
-        );
-
-        let flashlight = flashlight.map_or_else(
-            || vec![0.0; len],
-            |skill| mem::take(&mut skill.strain_peaks),
-        );
+        let [mut aim, mut aim_no_sliders, mut speed, mut flashlight] = skills;
 
         OsuStrains {
             section_len: SECTION_LEN * clock_rate,
-            aim: mem::take(&mut skills.aim().strain_peaks),
-            aim_no_sliders: mem::take(&mut skills.aim_no_sliders().strain_peaks),
-            speed,
-            flashlight,
+            aim: aim.take_strain_peaks(),
+            aim_no_sliders: aim_no_sliders.take_strain_peaks(),
+            speed: speed.take_strain_peaks(),
+            flashlight: flashlight.take_strain_peaks(),
         }
     }
 }
 
-/// The result of calculating the strains on a osu!taiko map.
+/// The result of calculating the strains on a osu! map.
 /// Suitable to plot the difficulty of a map over time.
 #[derive(Clone, Debug)]
 pub struct OsuStrains {
@@ -225,36 +226,7 @@ impl OsuStrains {
     }
 }
 
-fn calculate_star_rating(aim_rating: f64, speed_rating: f64, flashlight_rating: f64) -> f64 {
-    let base_aim_performance = {
-        let base = 5.0 * (aim_rating / 0.0675).max(1.0) - 4.0;
-
-        base * base * base / 100_000.0
-    };
-
-    let base_speed_performance = {
-        let base = 5.0 * (speed_rating / 0.0675).max(1.0) - 4.0;
-
-        base * base * base / 100_000.0
-    };
-
-    let base_flashlight_performance = flashlight_rating * flashlight_rating * 25.0;
-
-    let base_performance = (base_aim_performance.powf(1.1)
-        + base_speed_performance.powf(1.1)
-        + base_flashlight_performance.powf(1.1))
-    .powf(1.0 / 1.1);
-
-    if base_performance > 0.00001 {
-        1.12_f64.cbrt()
-            * 0.027
-            * ((100_000.0 / (1.0_f64 / 1.1).exp2() * base_performance).cbrt() + 4.0)
-    } else {
-        0.0
-    }
-}
-
-fn calculate_skills(params: OsuStars<'_>) -> (Skills, OsuDifficultyAttributes) {
+fn calculate_skills(params: OsuStars<'_>) -> ([Box<dyn Skill>; 4], OsuDifficultyAttributes) {
     let OsuStars {
         map,
         mods,
@@ -269,7 +241,7 @@ fn calculate_skills(params: OsuStars<'_>) -> (Skills, OsuDifficultyAttributes) {
     let scaling_factor = ScalingFactor::new(map_attributes.cs);
     let hr = mods.hr();
     let time_preempt = map_attributes.hit_windows.ar;
-    let hit_window = map_attributes.hit_windows.od;
+    let hit_window = 2.0 * map_attributes.hit_windows.od;
 
     let mut attributes = OsuDifficultyAttributes {
         ar: map_attributes.ar,
@@ -281,7 +253,6 @@ fn calculate_skills(params: OsuStars<'_>) -> (Skills, OsuDifficultyAttributes) {
     let mut params = ObjectParameters {
         map,
         attributes: &mut attributes,
-        slider_state: SliderState::new(map),
         ticks: Vec::new(),
         curve_bufs: CurveBuffers::default(),
     };
@@ -303,67 +274,70 @@ fn calculate_skills(params: OsuStars<'_>) -> (Skills, OsuDifficultyAttributes) {
         old_stacking(&mut hit_objects, stack_threshold);
     }
 
-    let mut hit_objects = hit_objects.into_iter().map(|mut h| {
+    let mut hit_objects = hit_objects.iter_mut().map(|h| {
         let stack_offset = scaling_factor.stack_offset(h.stack_height);
         h.pos += stack_offset;
 
         h
     });
 
-    let mut skills = Skills::new(hit_window, mods.rx(), scaling_factor.radius(), mods.fl());
+    let mut skills = create_skills(mods, scaling_factor.radius);
 
-    let (mut prev, curr) = match (hit_objects.next(), hit_objects.next()) {
-        (Some(prev), Some(curr)) => (prev, curr),
-        (Some(_), None) | (None, None) => return (skills, attributes),
-        (None, Some(_)) => unreachable!(),
+    let last = match hit_objects.next() {
+        Some(prev) => prev,
+        None => return (skills, attributes),
     };
 
-    let mut prev_prev = None;
+    let mut last_last = None;
 
-    // First object has no predecessor and thus no strain, handle distinctly
-    let mut curr_section_end = (prev.time / clock_rate / SECTION_LEN).ceil() * SECTION_LEN;
-
-    // Handle second object separately to remove later if-branching
-    let h = DifficultyObject::new(
-        &curr,
-        &mut prev,
-        prev_prev.as_ref(),
-        &scaling_factor,
-        clock_rate,
-    );
-
-    let base_time = h.base.time / clock_rate;
-
-    while base_time > curr_section_end {
-        skills.start_new_section_from(curr_section_end);
-        curr_section_end += SECTION_LEN;
+    // Prepare `lazy_travel_dist` and `lazy_end_pos` for `last` manually
+    if let OsuObjectKind::Slider {
+        lazy_travel_time,
+        lazy_end_pos,
+        nested_objects,
+        ..
+    } = &mut last.kind
+    {
+        Distances::compute_slider_cursor_pos(
+            last.pos,
+            last.start_time,
+            lazy_end_pos,
+            lazy_travel_time,
+            nested_objects,
+            &scaling_factor,
+        );
     }
 
-    skills.process(&h);
-    prev_prev = Some(mem::replace(&mut prev, curr));
+    let mut last = &*last;
+    let mut diff_objects = Vec::with_capacity(hit_objects.len().saturating_sub(2));
 
-    // Handle all other objects
-    for curr in hit_objects {
-        let h = DifficultyObject::new(
-            &curr,
-            &mut prev,
-            prev_prev.as_ref(),
-            &scaling_factor,
+    for (i, curr) in hit_objects.enumerate() {
+        let delta_time = (curr.start_time - last.start_time) / clock_rate;
+
+        // * Capped to 25ms to prevent difficulty calculation breaking from simultaneous objects.
+        let strain_time = delta_time.max(OsuDifficultyObject::MIN_DELTA_TIME as f64);
+
+        let dists = Distances::new(
+            curr,
+            last,
+            last_last,
             clock_rate,
+            strain_time,
+            &scaling_factor,
         );
 
-        let base_time = h.base.time / clock_rate;
+        let diff_obj = OsuDifficultyObject::new(curr, last, clock_rate, i, dists);
+        diff_objects.push(diff_obj);
 
-        while base_time > curr_section_end {
-            skills.save_peak_and_start_new_section(curr_section_end);
-            curr_section_end += SECTION_LEN;
-        }
-
-        skills.process(&h);
-        prev_prev = Some(mem::replace(&mut prev, curr));
+        last_last = Some(last);
+        last = &*curr;
     }
 
-    skills.save_current_peak();
+    for curr in diff_objects.iter() {
+        for skill in skills.iter_mut() {
+            skill.process(curr, &diff_objects, hit_window);
+        }
+    }
 
     (skills, attributes)
 }
@@ -406,7 +380,8 @@ fn stacking(hit_objects: &mut [OsuObject], stack_threshold: f64) {
 
                 if hit_objects[n].is_spinner() {
                     continue;
-                } else if hit_objects[obj_i_idx].time - hit_objects[n].end_time() > stack_threshold
+                } else if hit_objects[obj_i_idx].start_time - hit_objects[n].end_time()
+                    > stack_threshold
                 {
                     break; // * We are no longer within stacking range of the previous object.
                 }
@@ -466,7 +441,9 @@ fn stacking(hit_objects: &mut [OsuObject], stack_threshold: f64) {
 
                 if hit_objects[n].is_spinner() {
                     continue;
-                } else if hit_objects[obj_i_idx].time - hit_objects[n].time > stack_threshold {
+                } else if hit_objects[obj_i_idx].start_time - hit_objects[n].start_time
+                    > stack_threshold
+                {
                     break; // * We are no longer within stacking range of the previous object.
                 }
 
@@ -495,7 +472,7 @@ fn old_stacking(hit_objects: &mut [OsuObject], stack_threshold: f64) {
         let mut slider_stack = 0.0;
 
         for j in i + 1..hit_objects.len() {
-            if hit_objects[j].time - stack_threshold > start_time {
+            if hit_objects[j].start_time - stack_threshold > start_time {
                 break;
             }
 
@@ -511,21 +488,28 @@ fn old_stacking(hit_objects: &mut [OsuObject], stack_threshold: f64) {
     }
 }
 
-fn lerp(start: f64, end: f64, percent: f64) -> f64 {
-    start + (end - start) * percent
+fn create_skills(mods: u32, radius: f32) -> [Box<dyn Skill>; 4] {
+    [
+        Box::new(Aim::new(true)) as Box<dyn Skill>,
+        Box::new(Aim::new(false)) as Box<dyn Skill>,
+        Box::new(Speed::new()) as Box<dyn Skill>,
+        Box::new(Flashlight::new(mods, radius)) as Box<dyn Skill>,
+    ]
 }
 
 /// The result of a difficulty calculation on an osu!standard map.
 #[derive(Clone, Debug, Default, PartialEq)]
 pub struct OsuDifficultyAttributes {
     /// The aim portion of the total strain.
-    pub aim_strain: f64,
+    pub aim: f64,
     /// The speed portion of the total strain.
-    pub speed_strain: f64,
+    pub speed: f64,
     /// The flashlight portion of the total strain.
-    pub flashlight_rating: f64,
+    pub flashlight: f64,
     /// The ratio of the aim strain with and without considering sliders
     pub slider_factor: f64,
+    /// The number of clickable objects weighted by difficulty.
+    pub speed_note_count: f64,
     /// The approach rate.
     pub ar: f64,
     /// The overall difficulty
@@ -567,6 +551,8 @@ pub struct OsuPerformanceAttributes {
     pub pp_flashlight: f64,
     /// The speed portion of the final pp.
     pub pp_speed: f64,
+    /// Misses including an approximated amount of slider breaks
+    pub effective_miss_count: f64,
 }
 
 impl OsuPerformanceAttributes {

src/osu/osu_object.rs

@@ -1,8 +1,9 @@
 use std::{cmp::Ordering, convert::identity};
 
-use super::{slider_state::SliderState, OsuDifficultyAttributes};
+use super::OsuDifficultyAttributes;
 
 use crate::{
+    beatmap::DifficultyPoint,
     curve::{Curve, CurveBuffers},
     parse::{HitObject, HitObjectKind, Pos2},
     Beatmap,
@@ -13,9 +14,11 @@ const BASE_SCORING_DISTANCE: f64 = 100.0;
 
 #[derive(Clone, Debug)]
 pub(crate) struct OsuObject {
-    pub(crate) time: f64,
+    pub(crate) start_time: f64,
     pub(crate) pos: Pos2,
     pub(crate) stack_height: f32,
+    pub(crate) time_preempt: f64,
+    pub(crate) time_fade_in: f64,
     pub(crate) kind: OsuObjectKind,
 }
 
@@ -25,6 +28,7 @@ pub(crate) enum OsuObjectKind {
     Slider {
         end_time: f64,
         end_pos: Pos2,
+        lazy_travel_time: f64,
         lazy_end_pos: Pos2,
         nested_objects: Vec<NestedObject>,
     },
@@ -36,7 +40,7 @@ pub(crate) enum OsuObjectKind {
 #[derive(Clone, Debug)]
 pub(crate) struct NestedObject {
     pub(crate) pos: Pos2,
-    pub(crate) time: f64,
+    pub(crate) start_time: f64,
     pub(crate) kind: NestedObjectKind,
 }
 
@@ -51,18 +55,19 @@ pub(crate) struct ObjectParameters<'a> {
     pub(crate) map: &'a Beatmap,
     pub(crate) attributes: &'a mut OsuDifficultyAttributes,
     pub(crate) ticks: Vec<(Pos2, f64)>,
-    pub(crate) slider_state: SliderState<'a>,
     pub(crate) curve_bufs: CurveBuffers,
 }
 
 impl OsuObject {
-    #[allow(clippy::too_many_arguments)]
+    const PREEMPT_MIN: f64 = 450.0;
+    const TIME_PREEMPT: f64 = 600.0;
+    const TIME_FADE_IN: f64 = 400.0;
+
     pub(crate) fn new(h: &HitObject, hr: bool, params: &mut ObjectParameters<'_>) -> Option<Self> {
         let ObjectParameters {
             map,
             attributes,
             ticks,
-            slider_state,
             curve_bufs,
         } = params;
 
@@ -77,10 +82,27 @@ impl OsuObject {
             HitObjectKind::Circle => {
                 attributes.n_circles += 1;
 
+                // TODO: check if ar needs to be adjusted
+                let tmp_preempt =
+                    difficulty_range(map.ar as f64, 1800.0, 1200.0, Self::PREEMPT_MIN) as f32;
+                let time_preempt = tmp_preempt as f64;
+
+                // * Preempt time can go below 450ms. Normally, this is achieved via the DT mod
+                // * which uniformly speeds up all animations game wide regardless of AR.
+                // * This uniform speedup is hard to match 1:1, however we can at least make
+                // * AR>10 (via mods) feel good by extending the upper linear function above.
+                // * Note that this doesn't exactly match the AR>10 visuals as they're
+                // * classically known, but it feels good.
+                // * This adjustment is necessary for AR>10, otherwise TimePreempt can
+                // * become smaller leading to hitcircles not fully fading in.
+                let time_fade_in = 400.0 * (time_preempt / Self::PREEMPT_MIN).min(1.0);
+
                 Self {
-                    time: h.start_time,
+                    start_time: h.start_time,
                     pos,
                     stack_height: 0.0,
+                    time_preempt,
+                    time_fade_in,
                     kind: OsuObjectKind::Circle,
                 }
             }
@@ -92,30 +114,43 @@ impl OsuObject {
             } => {
                 attributes.n_sliders += 1;
 
-                // Responsible for timing point values
-                slider_state.update(h.start_time);
+                let timing_point = map.timing_point_at(h.start_time);
+                let difficulty_point = map.difficulty_point_at(h.start_time).unwrap_or_default();
 
-                let span_count = (*repeats + 1) as f64;
+                let scoring_dist =
+                    BASE_SCORING_DISTANCE * map.slider_mult * difficulty_point.slider_vel;
 
-                let mut tick_dist = 100.0 * map.slider_mult / map.tick_rate;
+                let vel = scoring_dist / timing_point.beat_len;
 
                 // * prior to v8, speed multipliers don't adjust for how many ticks are generated over the same distance.
                 // * this results in more (or less) ticks being generated in <v8 maps for the same time duration.
-                if map.version >= 8 {
-                    tick_dist /=
-                        (100.0 / slider_state.slider_velocity).max(10.0).min(1000.0) / 100.0;
-                }
+                let tick_dist_mult = if map.version < 8 {
+                    let first_slider_vel = map
+                        .difficulty_points
+                        .first()
+                        .map_or(DifficultyPoint::DEFAULT_SLIDER_VEL, |point| {
+                            point.slider_vel
+                        });
+
+                    first_slider_vel.recip()
+                } else {
+                    1.0
+                };
+
+                let mut tick_dist = if difficulty_point.generate_ticks {
+                    scoring_dist / map.tick_rate * tick_dist_mult
+                } else {
+                    f64::INFINITY
+                };
+
+                let span_count = (*repeats + 1) as f64;
 
                 // Build the curve w.r.t. the control points
                 let curve = Curve::new(control_points, *pixel_len, curve_bufs);
 
-                let velocity =
-                    (BASE_SCORING_DISTANCE * map.slider_mult * slider_state.slider_velocity)
-                        / slider_state.beat_len;
-
-                let end_time = h.start_time + span_count * curve.dist() / velocity;
-                let duration = end_time - h.start_time;
-                let span_duration = duration / span_count;
+                let end_time = h.start_time + span_count * curve.dist() / vel;
+                let total_duration = end_time - h.start_time;
+                let span_duration = total_duration / span_count;
 
                 // * A very lenient maximum length of a slider for ticks to be generated.
                 // * This exists for edge cases such as /b/1573664 where the beatmap has
@@ -124,101 +159,131 @@ impl OsuObject {
 
                 let len = curve.dist().min(max_len);
                 tick_dist = tick_dist.clamp(0.0, len);
-                let min_dist_from_end = velocity * 10.0;
+                let min_dist_from_end = vel * 10.0;
 
                 let mut curr_dist = tick_dist;
 
+                // TODO: check if ar needs to be adjusted
+                let tmp_preempt =
+                    difficulty_range(map.ar as f64, 1800.0, 1200.0, Self::PREEMPT_MIN) as f32;
+                let head_time_preempt = tmp_preempt as f64;
+
+                // * Preempt time can go below 450ms. Normally, this is achieved via the DT mod
+                // * which uniformly speeds up all animations game wide regardless of AR.
+                // * This uniform speedup is hard to match 1:1, however we can at least make
+                // * AR>10 (via mods) feel good by extending the upper linear function above.
+                // * Note that this doesn't exactly match the AR>10 visuals as they're
+                // * classically known, but it feels good.
+                // * This adjustment is necessary for AR>10, otherwise TimePreempt can
+                // * become smaller leading to hitcircles not fully fading in.
+                let head_time_fade_in = 400.0 * (head_time_preempt / Self::PREEMPT_MIN).min(1.0);
+
                 ticks.clear();
-                ticks.reserve((len / tick_dist) as usize);
-                let mut nested_objects =
-                    Vec::with_capacity((len * span_count / tick_dist) as usize);
 
-                // Ticks of the first span
-                while curr_dist < len - min_dist_from_end {
-                    let progress = curr_dist / len;
+                let mut nested_objects = if tick_dist != 0.0 {
+                    ticks.reserve((len / tick_dist) as usize);
+                    let mut nested_objects =
+                        Vec::with_capacity((len * span_count / tick_dist) as usize);
 
-                    let curr_time = h.start_time + progress * span_duration;
-                    let mut curr_pos = h.pos + curve.position_at(progress);
+                    // Ticks of the first span
+                    while curr_dist < len - min_dist_from_end {
+                        let progress = curr_dist / len;
 
-                    if hr {
-                        curr_pos.y = 384.0 - curr_pos.y;
-                    }
+                        let curr_time = h.start_time + progress * span_duration;
+                        let mut curr_pos = h.pos + curve.position_at(progress);
 
-                    let tick = NestedObject {
-                        pos: curr_pos,
-                        time: curr_time,
-                        kind: NestedObjectKind::Tick,
-                    };
+                        if hr {
+                            curr_pos.y = 384.0 - curr_pos.y;
+                        }
 
-                    nested_objects.push(tick);
-                    ticks.push((curr_pos, curr_time));
-
-                    curr_dist += tick_dist;
-                }
-
-                // Other spans
-                for span_idx in 1..=*repeats {
-                    let progress = (span_idx % 2 == 1) as u8 as f64;
-                    let span_idx_f64 = span_idx as f64;
-
-                    // Repeat point
-                    let curr_time = h.start_time + span_duration * span_idx_f64;
-                    let mut curr_pos = h.pos + curve.position_at(progress);
-
-                    if hr {
-                        curr_pos.y = 384.0 - curr_pos.y;
-                    }
-
-                    let repeat = NestedObject {
-                        pos: curr_pos,
-                        time: curr_time,
-                        kind: NestedObjectKind::Repeat,
-                    };
-
-                    nested_objects.push(repeat);
-
-                    // Ticks
-                    if span_idx & 1 == 1 {
-                        // S-------->R | Span 0
-                        //  2  4  6  8 | => span_duration = 8
-                        // R<--------- | Span 1
-                        // 16 14 12 10 | => offset = 1 * span_duration
-                        // --------->R | Span 2
-                        // 18 20 22 24 | => not reverse; simple case
-                        // T<--------- | Span 3
-                        // 32 30 28 26 | => offset = 3 * span_duration
-                        //
-                        //  n = offset + tick
-                        // 26 =   24   +   2
-                        // 28 =   24   +   4
-                        // 30 =   24   +   6
-                        // 32 =   24   +   8
-
-                        let offset = span_idx_f64 * span_duration;
-
-                        let tick_iter = ticks.iter().rev().zip(ticks.iter()).map(
-                            |((rev_pos, _), (_, time))| NestedObject {
-                                pos: *rev_pos,
-                                time: offset + time,
-                                kind: NestedObjectKind::Tick,
-                            },
-                        );
-
-                        nested_objects.extend(tick_iter);
-                    } else {
-                        let tick_iter = ticks.iter().map(|(pos, time)| NestedObject {
-                            pos: *pos,
-                            time: time + span_duration * span_idx_f64,
+                        let tick = NestedObject {
+                            pos: curr_pos,
+                            start_time: curr_time,
                             kind: NestedObjectKind::Tick,
-                        });
+                        };
 
-                        nested_objects.extend(tick_iter);
+                        nested_objects.push(tick);
+                        ticks.push((curr_pos, curr_time));
+
+                        curr_dist += tick_dist;
                     }
-                }
+
+                    // Other spans
+                    for span_idx in 1..=*repeats {
+                        let progress = (span_idx % 2 == 1) as u8 as f64;
+                        let span_idx_f64 = span_idx as f64;
+
+                        // Repeat point
+                        let curr_time = h.start_time + span_duration * span_idx_f64;
+                        let mut curr_pos = h.pos + curve.position_at(progress);
+
+                        if hr {
+                            curr_pos.y = 384.0 - curr_pos.y;
+                        }
+
+                        let repeat = NestedObject {
+                            pos: curr_pos,
+                            start_time: curr_time,
+                            kind: NestedObjectKind::Repeat,
+                        };
+
+                        nested_objects.push(repeat);
+
+                        // Ticks
+                        if span_idx & 1 == 1 {
+                            // S-------->R | Span 0
+                            //  2  4  6  8 | => span_duration = 8
+                            // R<--------- | Span 1
+                            // 16 14 12 10 | => offset = 1 * span_duration
+                            // --------->R | Span 2
+                            // 18 20 22 24 | => not reverse; simple case
+                            // T<--------- | Span 3
+                            // 32 30 28 26 | => offset = 3 * span_duration
+                            //
+                            //  n = offset + tick
+                            // 26 =   24   +   2
+                            // 28 =   24   +   4
+                            // 30 =   24   +   6
+                            // 32 =   24   +   8
+
+                            let offset = span_idx_f64 * span_duration;
+
+                            let tick_iter = ticks.iter().rev().zip(ticks.iter()).map(
+                                |((rev_pos, _), (_, time))| {
+                                    let start_time = offset + time;
+
+                                    NestedObject {
+                                        pos: *rev_pos,
+                                        start_time,
+                                        kind: NestedObjectKind::Tick,
+                                    }
+                                },
+                            );
+
+                            nested_objects.extend(tick_iter);
+                        } else {
+                            let tick_iter = ticks.iter().map(|(pos, time)| {
+                                let start_time = time + span_duration * span_idx_f64;
+
+                                NestedObject {
+                                    pos: *pos,
+                                    start_time,
+                                    kind: NestedObjectKind::Tick,
+                                }
+                            });
+
+                            nested_objects.extend(tick_iter);
+                        }
+                    }
+
+                    nested_objects
+                } else {
+                    Vec::new()
+                };
 
                 // Slider tail
                 let final_span_start_time = h.start_time + *repeats as f64 * span_duration;
-                let final_span_end_time = (h.start_time + duration / 2.0)
+                let final_span_end_time = (h.start_time + total_duration / 2.0)
                     .max(final_span_start_time + span_duration - LEGACY_LAST_TICK_OFFSET);
 
                 let progress = (*repeats % 2 == 0) as u8 as f64;
@@ -233,18 +298,18 @@ impl OsuObject {
                 // * if this is to change, we should revisit this.
                 let legacy_last_tick = NestedObject {
                     pos: end_pos,
-                    time: final_span_end_time,
+                    start_time: final_span_end_time,
                     kind: NestedObjectKind::Tail,
                 };
 
                 // On very short buzz sliders it can happen that the
                 // legacy last tick is not the last object time-wise
                 match nested_objects.last() {
-                    Some(last) if last.time > final_span_end_time => {
+                    Some(last) if last.start_time > final_span_end_time => {
                         let idx = nested_objects
                             .binary_search_by(|nested| {
                                 nested
-                                    .time
+                                    .start_time
                                     .partial_cmp(&final_span_end_time)
                                     .unwrap_or(Ordering::Equal)
                             })
@@ -257,7 +322,11 @@ impl OsuObject {
 
                 attributes.max_combo += nested_objects.len();
 
-                let lazy_travel_time = final_span_end_time - h.start_time;
+                let last_time = nested_objects
+                    .last()
+                    .map_or(final_span_end_time, |nested| nested.start_time);
+
+                let lazy_travel_time = last_time - h.start_time;
                 let mut end_time_min = lazy_travel_time / span_duration;
 
                 if end_time_min % 2.0 >= 1.0 {
@@ -274,13 +343,16 @@ impl OsuObject {
                 }
 
                 Self {
-                    time: h.start_time,
+                    start_time: h.start_time,
                     pos,
                     stack_height: 0.0,
+                    time_preempt: head_time_preempt,
+                    time_fade_in: head_time_fade_in,
                     kind: OsuObjectKind::Slider {
                         end_time,
                         end_pos,
                         lazy_end_pos,
+                        lazy_travel_time,
                         nested_objects,
                     },
                 }
@@ -289,9 +361,11 @@ impl OsuObject {
                 attributes.n_spinners += 1;
 
                 Self {
-                    time: h.start_time,
+                    start_time: h.start_time,
                     pos,
                     stack_height: 0.0,
+                    time_preempt: Self::TIME_PREEMPT,
+                    time_fade_in: Self::TIME_FADE_IN,
                     kind: OsuObjectKind::Spinner {
                         end_time: *end_time,
                     },
@@ -306,7 +380,7 @@ impl OsuObject {
     #[inline]
     pub(crate) fn end_time(&self) -> f64 {
         match &self.kind {
-            OsuObjectKind::Circle => self.time,
+            OsuObjectKind::Circle => self.start_time,
             OsuObjectKind::Slider { end_time, .. } => *end_time,
             OsuObjectKind::Spinner { end_time } => *end_time,
         }
@@ -343,3 +417,14 @@ impl OsuObject {
         matches!(self.kind, OsuObjectKind::Spinner { .. })
     }
 }
+
+// TODO: cleanup
+fn difficulty_range(difficulty: f64, min: f64, mid: f64, max: f64) -> f64 {
+    if difficulty > 5.0 {
+        mid + (max - mid) * (difficulty - 5.0) / 5.0
+    } else if difficulty < 5.0 {
+        mid - (mid - min) * (5.0 - difficulty) / 5.0
+    } else {
+        mid
+    }
+}

src/osu/pp.rs

@@ -1,4 +1,6 @@
-use super::{OsuDifficultyAttributes, OsuPerformanceAttributes, OsuScoreState};
+use super::{
+    OsuDifficultyAttributes, OsuPerformanceAttributes, OsuScoreState, PERFORMANCE_BASE_MULTIPLIER,
+};
 use crate::{
     AnyPP, Beatmap, DifficultyAttributes, GameMode, Mods, OsuStars, PerformanceAttributes,
 };
@@ -262,18 +264,19 @@ impl<'map> OsuPP<'map> {
             let total_hits = (n300 + n100 + n50 + self.n_misses).min(n_objects) as f64;
 
             let effective_misses =
-                calculate_effective_misses(&attributes, self.combo, self.n_misses, total_hits);
+                calculate_effective_misses(&attributes, self.combo, n100, n50, self.n_misses);
 
             OsuPPInner {
-                attributes,
                 mods: self.mods,
-                combo: self.combo,
+                combo: self.combo.unwrap_or(attributes.max_combo),
                 acc,
                 n300,
                 n100,
                 n50,
+                n_misses: self.n_misses,
                 total_hits,
-                effective_misses,
+                effective_miss_count: effective_misses,
+                attributes,
             }
         } else {
             let n_objects = self.passed_objects.unwrap_or(self.map.hit_objects.len());
@@ -313,18 +316,19 @@ impl<'map> OsuPP<'map> {
             let total_hits = (n300 + n100 + n50 + self.n_misses).min(n_objects) as f64;
 
             let effective_misses =
-                calculate_effective_misses(&attributes, self.combo, self.n_misses, total_hits);
+                calculate_effective_misses(&attributes, self.combo, n100, n50, self.n_misses);
 
             OsuPPInner {
-                attributes,
                 mods: self.mods,
-                combo: self.combo,
+                combo: self.combo.unwrap_or(attributes.max_combo),
                 acc,
                 n300,
                 n100,
                 n50,
+                n_misses: self.n_misses,
                 total_hits,
-                effective_misses,
+                effective_miss_count: effective_misses,
+                attributes,
             }
         }
     }
@@ -353,60 +357,69 @@ struct OsuPPInner {
     attributes: OsuDifficultyAttributes,
     mods: u32,
     acc: f64,
-    combo: Option<usize>,
+    combo: usize,
 
     n300: usize,
     n100: usize,
     n50: usize,
+    n_misses: usize,
 
     total_hits: f64,
-    effective_misses: usize,
+    effective_miss_count: f64,
 }
 
 impl OsuPPInner {
     fn calculate(mut self) -> OsuPerformanceAttributes {
-        let (aim_value, speed_value, acc_value, flashlight_value, pp) =
-            if self.total_hits.abs() <= f64::EPSILON {
-                (0.0, 0.0, 0.0, 0.0, 0.0)
-            } else {
-                let mut multiplier = 1.12;
-
-                // NF penalty
-                if self.mods.nf() {
-                    multiplier *= (1.0 - 0.02 * (self.effective_misses as f64)).max(0.9);
-                }
-
-                // SO penalty
-                if self.mods.so() {
-                    let n_spinners = self.attributes.n_spinners;
-                    multiplier *= 1.0 - (n_spinners as f64 / self.total_hits).powf(0.85);
-                }
-
-                // Relax penalty
-                if self.mods.rx() {
-                    // * As we're adding 100s and 50s to an approximated number of combo breaks\
-                    // * the result can be higher than total hits in specific scenarios
-                    // * (which breaks some calculations) so we need to clamp it.
-                    self.effective_misses = (self.effective_misses + self.n100 + self.n50)
-                        .min(self.total_hits as usize);
-
-                    multiplier *= 0.6;
-                }
-
-                let aim_value = self.compute_aim_value();
-                let speed_value = self.compute_speed_value();
-                let acc_value = self.compute_accuracy_value();
-                let flashlight_value = self.compute_flashlight_value();
-
-                let pp = (aim_value.powf(1.1)
-                    + speed_value.powf(1.1)
-                    + acc_value.powf(1.1)
-                    + flashlight_value.powf(1.1))
-                .powf(1.0 / 1.1)
-                    * multiplier;
-
-                (aim_value, speed_value, acc_value, flashlight_value, pp)
+        if self.total_hits.abs() <= f64::EPSILON {
+            return OsuPerformanceAttributes {
+                difficulty: self.attributes,
+                ..Default::default()
             };
+        }
+
+        let mut multiplier = PERFORMANCE_BASE_MULTIPLIER;
+
+        if self.mods.nf() {
+            multiplier *= (1.0 - 0.02 * self.effective_miss_count).max(0.9);
+        }
+
+        if self.mods.so() && self.total_hits > 0.0 {
+            multiplier *= 1.0 - (self.attributes.n_spinners as f64 / self.total_hits).powf(0.85);
+        }
+
+        if self.mods.rx() {
+            // * https://www.desmos.com/calculator/bc9eybdthb
+            // * we use OD13.3 as maximum since it's the value at which great hitwidow becomes 0
+            // * this is well beyond currently maximum achievable OD which is 12.17 (DTx2 + DA with OD11)
+            let (n100_mult, n50_mult) = if self.attributes.od > 0.0 {
+                (
+                    1.0 - (self.attributes.od / 13.33).powf(1.8),
+                    1.0 - (self.attributes.od / 13.33).powi(5),
+                )
+            } else {
+                (1.0, 1.0)
+            };
+
+            // * As we're adding Oks and Mehs to an approximated number of combo breaks the result can be
+            // * higher than total hits in specific scenarios (which breaks some calculations) so we need to clamp it.
+            self.effective_miss_count = (self.effective_miss_count
+                + self.n100 as f64
+                + n100_mult
+                + self.n50 as f64 * n50_mult)
+                .min(self.total_hits);
+        }
+
+        let aim_value = self.compute_aim_value();
+        let speed_value = self.compute_speed_value();
+        let acc_value = self.compute_accuracy_value();
+        let flashlight_value = self.compute_flashlight_value();
+
+        let pp = (aim_value.powf(1.1)
+            + speed_value.powf(1.1)
+            + acc_value.powf(1.1)
+            + flashlight_value.powf(1.1))
+        .powf(1.0 / 1.1)
+            * multiplier;
 
         OsuPerformanceAttributes {
             difficulty: self.attributes,
@@ -415,130 +428,133 @@ impl OsuPPInner {
             pp_flashlight: flashlight_value,
             pp_speed: speed_value,
             pp,
+            effective_miss_count: self.effective_miss_count,
         }
     }
 
     fn compute_aim_value(&self) -> f64 {
-        let attributes = &self.attributes;
-        let total_hits = self.total_hits;
+        let mut aim_value =
+            (5.0 * (self.attributes.aim / 0.0675).max(1.0) - 4.0).powi(3) / 100_000.0;
 
-        // TD penalty
-        let raw_aim = if self.mods.td() {
-            attributes.aim_strain.powf(0.8)
-        } else {
-            attributes.aim_strain
-        };
-
-        let mut aim_value = (5.0 * (raw_aim / 0.0675).max(1.0) - 4.0).powi(3) / 100_000.0;
-
-        // Longer maps are worth more
         let len_bonus = 0.95
-            + 0.4 * (total_hits / 2000.0).min(1.0)
-            + (total_hits > 2000.0) as u8 as f64 * 0.5 * (total_hits / 2000.0).log10();
+            + 0.4 * (self.total_hits / 2000.0).min(1.0)
+            + (self.total_hits > 2000.0) as u8 as f64 * (self.total_hits / 2000.0).log10() * 0.5;
+
         aim_value *= len_bonus;
 
-        // Penalize misses
-        let effective_misses = self.effective_misses as i32;
-        if effective_misses > 0 {
+        // * Penalize misses by assessing # of misses relative to the total # of objects.
+        // * Default a 3% reduction for any # of misses.
+        if self.effective_miss_count > 0.0 {
             aim_value *= 0.97
-                * (1.0 - (effective_misses as f64 / total_hits).powf(0.775)).powi(effective_misses);
+                * (1.0 - (self.effective_miss_count / self.total_hits).powf(0.775))
+                    .powf(self.effective_miss_count);
         }
 
-        // Combo scaling
-        if let Some(combo) = self.combo.filter(|_| attributes.max_combo > 0) {
-            aim_value *= ((combo as f64 / attributes.max_combo as f64).powf(0.8)).min(1.0);
-        }
+        aim_value *= self.get_combo_scaling_factor();
 
-        // AR bonus
-        let ar_factor = if attributes.ar > 10.33 {
-            0.3 * (attributes.ar - 10.33)
-        } else if attributes.ar < 8.0 {
-            0.1 * (8.0 - attributes.ar)
+        let ar_factor = if self.mods.rx() {
+            0.0
+        } else if self.attributes.ar > 10.33 {
+            0.3 * (self.attributes.ar - 10.33)
+        } else if self.attributes.ar < 8.0 {
+            0.05 * (8.0 - self.attributes.ar)
         } else {
             0.0
         };
 
-        aim_value *= 1.0 + ar_factor * len_bonus; // * Buff for longer maps with high AR.
+        // * Buff for longer maps with high AR.
+        aim_value *= 1.0 + ar_factor * len_bonus;
 
-        // HD bonus (this would include the Blinds mod but it's currently not representable)
         if self.mods.hd() {
-            aim_value *= 1.0 + 0.04 * (12.0 - attributes.ar);
+            // * We want to give more reward for lower AR when it comes to aim and HD. This nerfs high AR and buffs lower AR.
+            aim_value *= 1.0 + 0.04 * (12.0 - self.attributes.ar);
         }
 
-        if attributes.n_sliders > 0 {
-            // * We assume 15% of sliders in a map are difficult since
-            // * there's no way to tell from the performance calculator.
-            let estimate_difficult_sliders = attributes.n_sliders as f64 * 0.15;
+        // * We assume 15% of sliders in a map are difficult since there's no way to tell from the performance calculator.
+        let estimate_diff_sliders = self.attributes.n_sliders as f64 * 0.15;
 
-            let non_300s = self.total_hits - self.n300 as f64;
-            let missing_combo = attributes.max_combo - self.combo.unwrap_or(attributes.max_combo);
-
-            let estimate_slider_ends_dropped = non_300s
-                .min(missing_combo as f64)
-                .clamp(0.0, estimate_difficult_sliders);
-
-            let base = 1.0 - estimate_slider_ends_dropped / estimate_difficult_sliders;
-            let slider_nerf_factor =
-                (1.0 - attributes.slider_factor) * base * base * base + attributes.slider_factor;
+        if self.attributes.n_sliders > 0 {
+            let estimate_slider_ends_dropped = ((self.n100 + self.n50 + self.n_misses)
+                .min(self.attributes.max_combo - self.combo)
+                as f64)
+                .clamp(0.0, estimate_diff_sliders);
+            let slider_nerf_factor = (1.0 - self.attributes.slider_factor)
+                * (1.0 - estimate_slider_ends_dropped / estimate_diff_sliders).powi(3)
+                + self.attributes.slider_factor;
 
             aim_value *= slider_nerf_factor;
         }
 
         aim_value *= self.acc;
-        aim_value *= 0.98 + attributes.od * attributes.od / 2500.0;
+        // * It is important to consider accuracy difficulty when scaling with accuracy.
+        aim_value *= 0.98 + self.attributes.od * self.attributes.od / 2500.0;
 
         aim_value
     }
 
     fn compute_speed_value(&self) -> f64 {
-        let attributes = &self.attributes;
-        let total_hits = self.total_hits;
+        if self.mods.rx() {
+            return 0.0;
+        }
 
         let mut speed_value =
-            (5.0 * (attributes.speed_strain / 0.0675).max(1.0) - 4.0).powi(3) / 100_000.0;
+            (5.0 * (self.attributes.speed / 0.0675).max(1.0) - 4.0).powi(3) / 100_000.0;
 
-        // Longer maps are worth more
         let len_bonus = 0.95
-            + 0.4 * (total_hits / 2000.0).min(1.0)
-            + (total_hits > 2000.0) as u8 as f64 * 0.5 * (total_hits / 2000.0).log10();
+            + 0.4 * (self.total_hits / 2000.0).min(1.0)
+            + (self.total_hits > 2000.0) as u8 as f64 * (self.total_hits / 2000.0).log10() * 0.5;
+
         speed_value *= len_bonus;
 
-        // Penalize misses
-        let effective_misses = self.effective_misses as f64;
-        if effective_misses > 0.0 {
+        // * Penalize misses by assessing # of misses relative to the total # of objects.
+        // * Default a 3% reduction for any # of misses.
+        if self.effective_miss_count > 0.0 {
             speed_value *= 0.97
-                * (1.0 - (effective_misses / total_hits).powf(0.775))
-                    .powf(effective_misses.powf(0.875));
+                * (1.0 - (self.effective_miss_count / self.total_hits).powf(0.775))
+                    .powf(self.effective_miss_count.powf(0.875));
         }
 
-        // Combo scaling
-        if let Some(combo) = self.combo.filter(|_| attributes.max_combo > 0) {
-            speed_value *= ((combo as f64 / attributes.max_combo as f64).powf(0.8)).min(1.0);
-        }
+        speed_value *= self.get_combo_scaling_factor();
 
-        // AR bonus
-        let ar_factor = if attributes.ar > 10.33 {
-            0.3 * (attributes.ar - 10.33)
+        let ar_factor = if self.attributes.ar > 10.33 {
+            0.3 * (self.attributes.ar - 10.33)
         } else {
             0.0
         };
 
-        speed_value *= 1.0 + ar_factor * len_bonus; // * Buff for longer maps with high AR.
+        // * Buff for longer maps with high AR.
+        speed_value *= 1.0 + ar_factor * len_bonus;
 
-        // HD bonus (this would include the Blinds mod but it's currently not representable)
         if self.mods.hd() {
-            speed_value *= 1.0 + 0.04 * (12.0 - attributes.ar);
+            // * We want to give more reward for lower AR when it comes to aim and HD.
+            // * This nerfs high AR and buffs lower AR.
+            speed_value *= 1.0 + 0.04 * (12.0 - self.attributes.ar);
         }
 
-        // Scaling the speed value with accuracy and OD
-        let od_factor = 0.95 + attributes.od * attributes.od / 750.0;
-        let acc_factor = self.acc.powf((14.5 - attributes.od.max(8.0)) / 2.0);
-        speed_value *= od_factor * acc_factor;
+        // * Calculate accuracy assuming the worst case scenario
+        let relevant_total_diff = self.total_hits - self.attributes.speed_note_count;
+        let relevant_n300 = (self.n300 as f64 - relevant_total_diff).max(0.0);
+        let relevant_n100 =
+            (self.n100 as f64 - (relevant_total_diff - self.n300 as f64).max(0.0)).max(0.0);
+        let relevant_n50 = (self.n50 as f64
+            - (relevant_total_diff - (self.n300 + self.n100) as f64).max(0.0))
+        .max(0.0);
 
-        // Penalize n50s
-        speed_value *= 0.98_f64.powf(
-            (self.n50 as f64 >= total_hits / 500.0) as u8 as f64
-                * (self.n50 as f64 - total_hits / 500.0),
+        let relevant_acc = if self.attributes.speed_note_count.abs() <= f64::EPSILON {
+            0.0
+        } else {
+            (relevant_n300 * 6.0 + relevant_n100 * 2.0 + relevant_n50)
+                / (self.attributes.speed_note_count * 6.0)
+        };
+
+        // * Scale the speed value with accuracy and OD.
+        speed_value *= (0.95 + self.attributes.od * self.attributes.od / 750.0)
+            * ((self.acc + relevant_acc) / 2.0).powf((14.5 - (self.attributes.od).max(8.0)) / 2.0);
+
+        // * Scale the speed value with # of 50s to punish doubletapping.
+        speed_value *= 0.99_f64.powf(
+            (self.n50 as f64 >= self.total_hits / 500.0) as u8 as f64
+                * (self.n50 as f64 - self.total_hits / 500.0),
         );
 
         speed_value
@@ -549,28 +565,39 @@ impl OsuPPInner {
             return 0.0;
         }
 
-        let attributes = &self.attributes;
-        let total_hits = self.total_hits;
-        let n_circles = attributes.n_circles as f64;
-        let n300 = self.n300 as f64;
-        let n100 = self.n100 as f64;
-        let n50 = self.n50 as f64;
+        // * This percentage only considers HitCircles of any value - in this part
+        // * of the calculation we focus on hitting the timing hit window.
+        let amount_hit_objects_with_acc = self.attributes.n_circles;
 
-        let better_acc_percentage = (n_circles > 0.0) as u8 as f64
-            * (((n300 - (total_hits - n_circles)) * 6.0 + n100 * 2.0 + n50) / (n_circles * 6.0))
-                .max(0.0);
+        let mut better_acc_percentage = if amount_hit_objects_with_acc > 0 {
+            ((self.n300 - (self.total_hits as usize - amount_hit_objects_with_acc)) * 6
+                + self.n100 * 2
+                + self.n50) as f64
+                / (amount_hit_objects_with_acc * 6) as f64
+        } else {
+            0.0
+        };
 
-        let mut acc_value = 1.52163_f64.powf(attributes.od) * better_acc_percentage.powi(24) * 2.83;
+        // * It is possible to reach a negative accuracy with this formula. Cap it at zero - zero points.
+        if better_acc_percentage < 0.0 {
+            better_acc_percentage = 0.0;
+        }
 
-        // Bonus for many hitcircles
-        acc_value *= ((n_circles as f64 / 1000.0).powf(0.3)).min(1.15);
+        // * Lots of arbitrary values from testing.
+        // * Considering to use derivation from perfect accuracy in a probabilistic manner - assume normal distribution.
+        let mut acc_value =
+            1.52163_f64.powf(self.attributes.od) * better_acc_percentage.powi(24) * 2.83;
 
-        // HD bonus (this would include the Blinds mod but it's currently not representable)
+        // * Bonus for many hitcircles - it's harder to keep good accuracy up for longer.
+        acc_value *= (amount_hit_objects_with_acc as f64 / 1000.0)
+            .powf(0.3)
+            .min(1.15);
+
+        // * Increasing the accuracy value by object count for Blinds isn't ideal, so the minimum buff is given.
         if self.mods.hd() {
             acc_value *= 1.08;
         }
 
-        // FL bonus
         if self.mods.fl() {
             acc_value *= 1.02;
         }
@@ -583,76 +610,66 @@ impl OsuPPInner {
             return 0.0;
         }
 
-        let attributes = &self.attributes;
-        let total_hits = self.total_hits;
+        let mut flashlight_value = self.attributes.flashlight * self.attributes.flashlight * 25.0;
 
-        // TD penalty
-        let raw_flashlight = if self.mods.td() {
-            attributes.flashlight_rating.powf(0.8)
-        } else {
-            attributes.flashlight_rating
-        };
-
-        let mut flashlight_value = raw_flashlight * raw_flashlight * 25.0;
-
-        // Add an additional bonus for HDFL
-        if self.mods.hd() {
-            flashlight_value *= 1.3;
-        }
-
-        // Penalize misses by assessing # of misses relative to the total # of objects.
-        // Default a 3% reduction for any # of misses
-        let effective_misses = self.effective_misses as f64;
-        if effective_misses > 0.0 {
+        // * Penalize misses by assessing # of misses relative to the total # of objects. Default a 3% reduction for any # of misses.
+        if self.effective_miss_count > 0.0 {
             flashlight_value *= 0.97
-                * (1.0 - (effective_misses / total_hits).powf(0.775))
-                    .powf(effective_misses.powf(0.875));
+                * (1.0 - (self.effective_miss_count / self.total_hits).powf(0.775))
+                    .powf(self.effective_miss_count.powf(0.875));
         }
 
-        // Combo scaling
-        if let Some(combo) = self.combo.filter(|_| attributes.max_combo > 0) {
-            flashlight_value *= ((combo as f64 / attributes.max_combo as f64).powf(0.8)).min(1.0);
-        }
+        flashlight_value *= self.get_combo_scaling_factor();
 
-        // Account for shorter maps having a higher ratio of 0 combo/100 combo flashlight radius
+        // * Account for shorter maps having a higher ratio of 0 combo/100 combo flashlight radius.
         flashlight_value *= 0.7
-            + 0.1 * (total_hits / 200.0).min(1.0)
-            + (total_hits > 200.0) as u8 as f64 * (0.2 * ((total_hits - 200.0) / 200.0).min(1.0));
+            + 0.1 * (self.total_hits / 200.0).min(1.0)
+            + (self.total_hits > 200.0) as u8 as f64
+                * 0.2
+                * ((self.total_hits - 200.0) / 200.0).min(1.0);
 
-        // Scale the aim value with accuracy _slightly_
+        // * Scale the flashlight value with accuracy _slightly_.
         flashlight_value *= 0.5 + self.acc / 2.0;
-
-        // It is important to also consider accuracy difficulty when doing that
-        flashlight_value *= 0.98 + attributes.od * attributes.od / 2500.0;
+        // * It is important to also consider accuracy difficulty when doing that.
+        flashlight_value *= 0.98 + self.attributes.od * self.attributes.od / 2500.0;
 
         flashlight_value
     }
+
+    fn get_combo_scaling_factor(&self) -> f64 {
+        if self.attributes.max_combo == 0 {
+            1.0
+        } else {
+            ((self.combo as f64).powf(0.8) / (self.attributes.max_combo as f64).powf(0.8)).min(1.0)
+        }
+    }
 }
 
 fn calculate_effective_misses(
-    attributes: &OsuDifficultyAttributes,
+    attrs: &OsuDifficultyAttributes,
     combo: Option<usize>,
+    n100: usize,
+    n50: usize,
     n_misses: usize,
-    total_hits: f64,
-) -> usize {
+) -> f64 {
     // * Guess the number of misses + slider breaks from combo
-    let mut combo_based_misses: f64 = 0.0;
+    let mut combo_based_miss_count = 0.0;
 
-    if attributes.n_sliders > 0 {
-        let full_combo_threshold = attributes.max_combo as f64 - 0.1 * attributes.n_sliders as f64;
+    if attrs.n_sliders > 0 {
+        let full_combo_threshold = attrs.max_combo as f64 - 0.1 * attrs.n_sliders as f64;
 
-        let f64_combo = combo.map(|c| c as f64);
-
-        if let Some(combo) = f64_combo.filter(|&c| c < full_combo_threshold) {
-            combo_based_misses = full_combo_threshold / combo.max(1.0);
+        if let Some(score_max_combo) = combo
+            .map(|combo| combo as f64)
+            .filter(|&combo| combo < full_combo_threshold)
+        {
+            combo_based_miss_count = full_combo_threshold / score_max_combo.max(1.0);
         }
     }
 
-    // * Clamp misscount since it's derived from combo and can be
-    // * higher than total hits and that breaks some calculations
-    combo_based_misses = combo_based_misses.min(total_hits);
+    // * Clamp miss count to maximum amount of possible breaks
+    combo_based_miss_count = combo_based_miss_count.min((n100 + n50 + n_misses) as f64);
 
-    n_misses.max(combo_based_misses.floor() as usize)
+    combo_based_miss_count.max(n_misses as f64)
 }
 
 /// Abstract type to provide flexibility when passing difficulty attributes to a performance calculation.

src/osu/scaling_factor.rs

@@ -6,9 +6,8 @@ const OBJECT_RADIUS: f32 = 64.0;
 
 #[derive(Copy, Clone, Debug)]
 pub(crate) struct ScalingFactor {
-    adjusted_factor: f32,
-    factor: f32,
-    radius: f32,
+    pub(crate) factor: f32,
+    pub(crate) radius: f32,
     scale: f32,
 }
 
@@ -19,32 +18,19 @@ impl ScalingFactor {
         let radius = OBJECT_RADIUS * scale;
         let factor = NORMALIZED_RADIUS / radius;
 
-        let adjusted_factor = if radius < 30.0 {
+        let factor = if radius < 30.0 {
             factor * (1.0 + (30.0 - radius).min(5.0) / 50.0)
         } else {
             factor
         };
 
         Self {
-            adjusted_factor,
             factor,
             radius,
             scale: scale * -6.4,
         }
     }
 
-    pub(crate) fn raw(&self) -> f64 {
-        self.factor as f64
-    }
-
-    pub(crate) fn adjusted(&self) -> f32 {
-        self.adjusted_factor
-    }
-
-    pub(crate) fn radius(&self) -> f32 {
-        self.radius
-    }
-
     pub(crate) fn stack_offset(&self, stack_height: f32) -> Pos2 {
         Pos2::new(stack_height * self.scale)
     }

src/osu/skill.rs

@@ -131,7 +131,7 @@ impl Skill {
     pub(crate) fn process(&mut self, curr: &DifficultyObject<'_>) {
         self.kind.pre_process();
         self.curr_section_peak = self.strain_value_at(curr).max(self.curr_section_peak);
-        self.prev_time = Some(curr.base.time / curr.clock_rate);
+        self.prev_time = Some(curr.base.start_time / curr.clock_rate);
         self.kind.post_process(curr);
     }
 

src/osu/skill_kind.rs

@@ -1,580 +0,0 @@
-use std::{
-    collections::VecDeque,
-    f64::consts::{FRAC_PI_2, PI},
-    fmt, iter,
-};
-
-use crate::parse::Pos2;
-
-use super::{lerp, DifficultyObject};
-
-const SINGLE_SPACING_TRESHOLD: f64 = 125.0;
-
-const SPEED_BALANCING_FACTOR: f64 = 40.0;
-
-const AIM_SKILL_MULTIPLIER: f64 = 23.25;
-const AIM_STRAIN_DECAY_BASE: f64 = 0.15;
-const AIM_DECAY_WEIGHT: f64 = 0.9;
-const AIM_DIFFICULTY_MULTIPLIER: f64 = 1.06;
-const AIM_REDUCED_SECTION_COUNT: usize = 10;
-
-const AIM_HISTORY_LENGTH: usize = 2;
-const AIM_WIDE_ANGLE_MULTIPLIER: f64 = 1.5;
-const AIM_ACUTE_ANGLE_MULTIPLIER: f64 = 2.0;
-const AIM_SLIDER_MULTIPLIER: f64 = 1.5;
-const AIM_VELOCITY_CHANGE_MULTIPLIER: f64 = 0.75;
-
-const SPEED_SKILL_MULTIPLIER: f64 = 1375.0;
-const SPEED_STRAIN_DECAY_BASE: f64 = 0.3;
-const SPEED_DECAY_WEIGHT: f64 = 0.9;
-const SPEED_DIFFICULTY_MULTIPLIER: f64 = 1.04;
-const SPEED_REDUCED_SECTION_COUNT: usize = 5;
-
-const SPEED_HISTORY_LENGTH: usize = 32;
-const SPEED_RHYTHM_MULTIPLIER: f64 = 0.75;
-const SPEED_HISTORY_TIME_MAX: f64 = 5000.0; // * 5 seconds of calculate_speed_rhythm_bonus max
-const MIN_SPEED_BONUS: f64 = 75.0; // * ~200BPM
-
-const FLASHLIGHT_SKILL_MULTIPLIER: f64 = 0.15;
-const FLASHLIGHT_STRAIN_DECAY_BASE: f64 = 0.15;
-const FLASHLIGHT_DECAY_WEIGHT: f64 = 1.0;
-const FLASHLIGHT_DIFFICULTY_MULTIPLIER: f64 = 1.06;
-const FLASHLIGHT_REDUCED_SECTION_COUNT: usize = 10;
-
-const FLASHLIGHT_HISTORY_LENGTH: usize = 10;
-
-#[derive(Clone)]
-pub(crate) struct AimHistoryEntry {
-    angle: Option<f64>,
-    is_slider: bool,
-    is_spinner: bool,
-    strain_time: f64,
-    jump_dist: f64,
-    movement_dist: f64,
-    movement_time: f64,
-    travel_dist: f64,
-    travel_time: f64,
-}
-
-impl From<&DifficultyObject<'_>> for AimHistoryEntry {
-    fn from(h: &DifficultyObject<'_>) -> Self {
-        Self {
-            angle: h.angle,
-            is_slider: h.base.is_slider(),
-            is_spinner: h.base.is_spinner(),
-            strain_time: h.strain_time,
-            jump_dist: h.jump_dist,
-            movement_dist: h.movement_dist,
-            movement_time: h.movement_time,
-            travel_dist: h.travel_dist,
-            travel_time: h.travel_time,
-        }
-    }
-}
-
-#[derive(Clone)]
-pub(crate) struct FlashlightHistoryEntry {
-    end_pos: Pos2,
-    is_spinner: bool,
-    jump_dist: f64,
-    strain_time: f64,
-}
-
-impl From<&DifficultyObject<'_>> for FlashlightHistoryEntry {
-    fn from(h: &DifficultyObject<'_>) -> Self {
-        Self {
-            end_pos: h.base.end_pos(),
-            is_spinner: h.base.is_spinner(),
-            jump_dist: h.jump_dist,
-            strain_time: h.strain_time,
-        }
-    }
-}
-
-#[derive(Clone, Debug)]
-pub(crate) struct SpeedHistoryEntry {
-    is_slider: bool,
-    start_time: f64,
-    strain_time: f64,
-}
-
-impl From<&DifficultyObject<'_>> for SpeedHistoryEntry {
-    fn from(h: &DifficultyObject<'_>) -> Self {
-        Self {
-            is_slider: h.base.is_slider(),
-            start_time: h.base.time / h.clock_rate,
-            strain_time: h.strain_time,
-        }
-    }
-}
-
-#[derive(Clone)]
-pub(crate) enum SkillKind {
-    Aim {
-        history: VecDeque<AimHistoryEntry>,
-        with_sliders: bool,
-    },
-    Flashlight {
-        history: VecDeque<FlashlightHistoryEntry>,
-        scaling_factor: f64,
-    },
-    Speed {
-        curr_rhythm: f64,
-        history: VecDeque<SpeedHistoryEntry>,
-        hit_window: f64,
-    },
-}
-
-impl SkillKind {
-    pub(crate) fn aim(with_sliders: bool) -> Self {
-        Self::Aim {
-            history: VecDeque::with_capacity(AIM_HISTORY_LENGTH + 1),
-            with_sliders,
-        }
-    }
-
-    pub(crate) fn flashlight(scaling_factor: f64) -> Self {
-        Self::Flashlight {
-            history: VecDeque::with_capacity(FLASHLIGHT_HISTORY_LENGTH + 1),
-            scaling_factor,
-        }
-    }
-
-    pub(crate) fn speed(hit_window: f64) -> Self {
-        Self::Speed {
-            curr_rhythm: 1.0,
-            history: VecDeque::with_capacity(SPEED_HISTORY_LENGTH + 1),
-            hit_window,
-        }
-    }
-
-    pub(crate) fn pre_process(&mut self) {
-        match self {
-            Self::Aim { history, .. } => history.truncate(AIM_HISTORY_LENGTH),
-            Self::Flashlight { history, .. } => history.truncate(FLASHLIGHT_HISTORY_LENGTH),
-            Self::Speed { history, .. } => history.truncate(SPEED_HISTORY_LENGTH),
-        }
-    }
-
-    pub(crate) fn post_process(&mut self, current: &DifficultyObject<'_>) {
-        match self {
-            Self::Aim { history, .. } => history.push_front(current.into()),
-            Self::Flashlight { history, .. } => history.push_front(current.into()),
-            Self::Speed { history, .. } => history.push_front(current.into()),
-        }
-    }
-
-    pub(crate) fn strain_value_of(&self, curr: &DifficultyObject<'_>) -> f64 {
-        match self {
-            Self::Aim {
-                history,
-                with_sliders,
-            } => {
-                if curr.base.is_spinner() || history.len() < 2 || history[0].is_spinner {
-                    return 0.0;
-                }
-
-                let prev = &history[0];
-                let prev_prev = &history[1];
-
-                // * Calculate the velocity to the current hitobject,
-                // * which starts with a base distance / time assuming the last object is a hitcircle.
-                let mut curr_velocity = curr.jump_dist / curr.strain_time;
-
-                // * But if the last object is a slider, then we extend the
-                // * travel velocity through the slider into the current object.
-                if prev.is_slider && *with_sliders {
-                    // * calculate the movement velocity from slider end to current object
-                    let movement_velocity = curr.movement_dist / curr.movement_time;
-
-                    // * calculate the slider velocity from slider head to slider end.
-                    let travel_velocity = curr.travel_dist / curr.travel_time;
-
-                    // * take the larger total combined velocity.
-                    curr_velocity = curr_velocity.max(movement_velocity + travel_velocity);
-                }
-
-                // * As above, do the same for the previous hitobject.
-                let mut prev_velocity = prev.jump_dist / prev.strain_time;
-
-                if prev_prev.is_slider && *with_sliders {
-                    let movement_velocity = prev.movement_dist / prev.movement_time;
-                    let travel_velocity = prev.travel_dist / prev.travel_time;
-                    prev_velocity = prev_velocity.max(movement_velocity + travel_velocity);
-                }
-
-                let mut wide_angle_bonus = 0.0;
-                let mut acute_angle_bonus = 0.0;
-                let mut slider_bonus = 0.0;
-                let mut velocity_change_bonus = 0.0;
-
-                // * Start strain with regular velocity
-                let mut aim_strain = curr_velocity;
-
-                // * If rhythms are the same.
-                if curr.strain_time.max(prev.strain_time)
-                    < 1.25 * curr.strain_time.min(prev.strain_time)
-                {
-                    if let (Some(curr_angle), Some(prev_angle), Some(prev_prev_angle)) =
-                        (curr.angle, prev.angle, prev_prev.angle)
-                    {
-                        // * Rewarding angles, take the smaller velocity as base.
-                        let angle_bonus = curr_velocity.min(prev_velocity);
-
-                        wide_angle_bonus = calculate_wide_angle_bonus(curr_angle);
-
-                        // * Only bufff delta_time exceeding 300 bpm 1/2.
-                        if curr.strain_time <= 100.0 {
-                            let curr_bonus = calculate_acute_angle_bonus(curr_angle);
-
-                            // * Multiply by previous angle, we don't want to buff unless this is a wiggle type pattern.
-                            let prev_bonus = calculate_acute_angle_bonus(prev_angle);
-
-                            // * The maximum velocity we buff is equal to 125 / strainTime
-                            let angle_bonus = angle_bonus.min(125.0 / curr.strain_time);
-
-                            // * scale buff from 150 bpm 1/4 to 200 bpm 1/4
-                            let base1 =
-                                (FRAC_PI_2 * ((100.0 - curr.strain_time) / 25.0).min(1.0)).sin();
-
-                            // * Buff distance exceeding 50 (radius) up to 100 (diameter).
-                            let base2 = (FRAC_PI_2 * (curr.jump_dist.clamp(50.0, 100.0) - 50.0)
-                                / 50.0)
-                                .sin();
-
-                            acute_angle_bonus = curr_bonus
-                                * prev_bonus
-                                * angle_bonus
-                                * base1
-                                * base1
-                                * base2
-                                * base2
-                        }
-
-                        // * Penalize wide angles if they're repeated,
-                        // * reducing the penalty as the lastAngle gets more acute.
-                        let base = calculate_wide_angle_bonus(prev_angle);
-                        wide_angle_bonus *=
-                            angle_bonus * (1.0 - wide_angle_bonus.min(base * base * base));
-
-                        // * Penalize acute angles if they're repeated,
-                        // * reducing the penalty as the lastLastAngle gets more obtuse.
-                        let base = calculate_acute_angle_bonus(prev_prev_angle);
-                        acute_angle_bonus *=
-                            0.5 + 0.5 * (1.0 - acute_angle_bonus.min(base * base * base));
-                    }
-                }
-
-                if prev_velocity.max(curr_velocity).abs() > f64::EPSILON {
-                    // * We want to use the average velocity over the whole object when
-                    // * awarding differences, not the individual jump and slider path velocities.
-                    prev_velocity = (prev.jump_dist + prev.travel_dist) / prev.strain_time;
-                    curr_velocity = (curr.jump_dist + curr.travel_dist) / curr.strain_time;
-
-                    let velocity_diff = (prev_velocity - curr_velocity).abs();
-
-                    // * Scale with ratio of difference compared to 0.5 * max dist.
-                    let base = (FRAC_PI_2 * velocity_diff / prev_velocity.max(curr_velocity)).sin();
-                    let dist_ratio = base * base;
-
-                    // * Reward for % distance up to 125 / strainTime
-                    // * for overlaps where velocity is still changing.
-                    let overlap_velocity_buff =
-                        velocity_diff.min(125.0 / curr.strain_time.min(prev.strain_time));
-
-                    // * Reward for % distance slowed down compared to previous,
-                    // * paying attention to not award overlap
-                    let base =
-                        (FRAC_PI_2 * (curr.jump_dist.min(prev.jump_dist) / 100.0).min(1.0)).sin();
-                    let non_overlap_velocity_buff = velocity_diff * base * base;
-
-                    // * Choose the largest bonus, multiplied by ratio.
-                    velocity_change_bonus =
-                        overlap_velocity_buff.max(non_overlap_velocity_buff) * dist_ratio;
-
-                    // * Penalize for rhythm changes.
-                    let base = curr.strain_time.min(prev.strain_time)
-                        / curr.strain_time.max(prev.strain_time);
-                    velocity_change_bonus *= base * base;
-                }
-
-                if curr.travel_time.abs() > f64::EPSILON {
-                    // * Reward sliders based on velocity
-                    slider_bonus = curr.travel_dist / curr.travel_time;
-                }
-
-                // * Add in acute angle bonus or wide angle bonus + velocity change bonus,
-                // * whichever is larger
-                aim_strain += (acute_angle_bonus * AIM_ACUTE_ANGLE_MULTIPLIER).max(
-                    wide_angle_bonus * AIM_WIDE_ANGLE_MULTIPLIER
-                        + velocity_change_bonus * AIM_VELOCITY_CHANGE_MULTIPLIER,
-                );
-
-                // * Add in additional slider velocity bonus.
-                if *with_sliders {
-                    aim_strain += slider_bonus * AIM_SLIDER_MULTIPLIER;
-                }
-
-                aim_strain
-            }
-            Self::Flashlight {
-                history,
-                scaling_factor,
-            } => {
-                if curr.base.is_spinner() {
-                    return 0.0;
-                }
-
-                let mut small_dist_nerf = 1.0;
-                let mut result = 0.0;
-                let mut cumulative_strain_time = 0.0;
-                let mut history = history.iter();
-
-                if let Some(prev) = history.next() {
-                    // Handle first entry distinctly for slight optimization
-                    if !prev.is_spinner {
-                        let jump_dist = (curr.base.pos - prev.end_pos).length() as f64;
-                        cumulative_strain_time += prev.strain_time;
-
-                        // * We want to nerf objects that can be easily seen within the Flashlight circle radius
-                        small_dist_nerf = (jump_dist / 75.0).min(1.0);
-
-                        // * We also want to nerf stacks so that only the first object of the stack is accounted for
-                        let stack_nerf = ((prev.jump_dist / scaling_factor) / 25.0).min(1.0);
-
-                        result += stack_nerf * scaling_factor * jump_dist / cumulative_strain_time;
-                    }
-
-                    let factors = iter::successors(Some(0.8), |s| Some(s * 0.8));
-
-                    for (factor, prev) in factors.zip(history) {
-                        if !prev.is_spinner {
-                            let jump_dist = (curr.base.pos - prev.end_pos).length() as f64;
-                            cumulative_strain_time += prev.strain_time;
-
-                            // * We also want to nerf stacks so that only the first object of the stack is accounted for
-                            let stack_nerf = ((prev.jump_dist / scaling_factor) / 25.0).min(1.0);
-
-                            result += factor * stack_nerf * scaling_factor * jump_dist
-                                / cumulative_strain_time;
-                        }
-                    }
-                }
-
-                result *= small_dist_nerf;
-
-                result * result
-            }
-            Self::Speed {
-                history,
-                hit_window,
-                ..
-            } => {
-                if curr.base.is_spinner() {
-                    return 0.0;
-                }
-
-                let mut strain_time = curr.strain_time;
-                let hit_window_full = hit_window * 2.0;
-                let speed_window_ratio = strain_time / hit_window_full;
-                let prev = history.front();
-
-                // * Aim to nerf cheesy rhythms (very fast consecutive doubles with large delta times between)
-                if let Some(prev) =
-                    prev.filter(|p| strain_time < hit_window_full && p.strain_time > strain_time)
-                {
-                    strain_time = lerp(prev.strain_time, strain_time, speed_window_ratio);
-                }
-
-                // * Cap delta time to the OD 300 hit window
-                // * 0.93 is derived from making sure 260bpm OD8 streams aren't nerfed harshly,
-                // * whilst 0.92 limits the effect of the cap
-                strain_time /= (strain_time / hit_window_full / 0.93).clamp(0.92, 1.0);
-
-                // * Derive speed bonus for calculation
-                let mut speed_bonus = 1.0;
-
-                if strain_time < MIN_SPEED_BONUS {
-                    let base = (MIN_SPEED_BONUS - strain_time) / SPEED_BALANCING_FACTOR;
-                    speed_bonus = 1.0 + 0.75 * base * base;
-                }
-
-                let dist = SINGLE_SPACING_TRESHOLD.min(curr.travel_dist + curr.jump_dist);
-
-                (speed_bonus + speed_bonus * (dist / SINGLE_SPACING_TRESHOLD).powf(3.5))
-                    / strain_time
-            }
-        }
-    }
-
-    #[inline]
-    pub(crate) fn difficulty_values(&self) -> (usize, f64) {
-        match self {
-            Self::Aim { .. } => (AIM_REDUCED_SECTION_COUNT, AIM_DIFFICULTY_MULTIPLIER),
-            Self::Flashlight { .. } => (
-                FLASHLIGHT_REDUCED_SECTION_COUNT,
-                FLASHLIGHT_DIFFICULTY_MULTIPLIER,
-            ),
-            Self::Speed { .. } => (SPEED_REDUCED_SECTION_COUNT, SPEED_DIFFICULTY_MULTIPLIER),
-        }
-    }
-
-    #[inline]
-    pub(crate) fn skill_multiplier(&self) -> f64 {
-        match self {
-            SkillKind::Aim { .. } => AIM_SKILL_MULTIPLIER,
-            SkillKind::Flashlight { .. } => FLASHLIGHT_SKILL_MULTIPLIER,
-            SkillKind::Speed { .. } => SPEED_SKILL_MULTIPLIER,
-        }
-    }
-
-    #[inline]
-    pub(crate) fn strain_decay_base(&self) -> f64 {
-        match self {
-            SkillKind::Aim { .. } => AIM_STRAIN_DECAY_BASE,
-            SkillKind::Flashlight { .. } => FLASHLIGHT_STRAIN_DECAY_BASE,
-            SkillKind::Speed { .. } => SPEED_STRAIN_DECAY_BASE,
-        }
-    }
-
-    #[inline]
-    pub(crate) fn decay_weight(&self) -> f64 {
-        match self {
-            SkillKind::Aim { .. } => AIM_DECAY_WEIGHT,
-            SkillKind::Flashlight { .. } => FLASHLIGHT_DECAY_WEIGHT,
-            SkillKind::Speed { .. } => SPEED_DECAY_WEIGHT,
-        }
-    }
-
-    #[inline]
-    pub(crate) fn strain_decay(&self, ms: f64) -> f64 {
-        self.strain_decay_base().powf(ms / 1000.0)
-    }
-}
-
-pub(crate) fn calculate_speed_rhythm_bonus(
-    current: &DifficultyObject<'_>,
-    history: &VecDeque<SpeedHistoryEntry>,
-    hit_window: f64,
-) -> f64 {
-    if current.base.is_spinner() {
-        return 0.0;
-    }
-
-    let mut prev_island_size = 0;
-    let mut rhythm_complexity_sum = 0.0;
-    let mut island_size = 1;
-    let mut first_delta_switch = false;
-    let adjusted_hit_window = hit_window * 0.6;
-    let history_len = history.len() as f64;
-
-    // * Store the ratio of the current start of an island to buff for tighter rhythms
-    let mut start_ratio = 0.0;
-
-    let currs = history.iter();
-    let prevs = history.iter().skip(1);
-    let lasts = history.iter().skip(2);
-
-    for (((prev, curr), last), i) in prevs.zip(currs).zip(lasts).rev().zip(2..) {
-        let mut curr_historical_decay = (SPEED_HISTORY_TIME_MAX
-            - (current.base.time / current.clock_rate - curr.start_time))
-            .max(0.0)
-            / SPEED_HISTORY_TIME_MAX;
-
-        if curr_historical_decay.abs() > f64::EPSILON {
-            // * Either we're limited by time or limited by object count
-            curr_historical_decay = curr_historical_decay.min(i as f64 / history_len);
-
-            let curr_delta = curr.strain_time;
-            let prev_delta = prev.strain_time;
-            let last_delta = last.strain_time;
-
-            // * Fancy function to calculate rhythm bonuses
-            let base = (PI / (prev_delta.min(curr_delta) / prev_delta.max(curr_delta))).sin();
-            let curr_ratio = 1.0 + 6.0 * (base * base).min(0.5);
-
-            let lower_penalty = ((prev_delta - curr_delta).abs() - adjusted_hit_window).max(0.0);
-            let window_penalty = (lower_penalty / adjusted_hit_window).min(1.0);
-
-            let mut effective_ratio = window_penalty * curr_ratio;
-
-            if first_delta_switch {
-                if !(prev_delta > 1.25 * curr_delta || prev_delta * 1.25 < curr_delta) {
-                    if island_size < 7 {
-                        island_size += 1;
-                    }
-                } else {
-                    if curr.is_slider {
-                        // * bpm change is into slider, this is easy acc window
-                        effective_ratio *= 0.125;
-                    }
-
-                    if prev.is_slider {
-                        // * bpm change was from a slider, this is easier typically than circle -> circle
-                        effective_ratio *= 0.25;
-                    }
-
-                    if prev_island_size == island_size {
-                        // * repeated island size (ex: triplet -> triplet)
-                        effective_ratio *= 0.25;
-                    }
-
-                    if prev_island_size % 2 == island_size % 2 {
-                        // * repeated island polarity (2 -> 4, 3 -> 5)
-                        effective_ratio *= 0.5;
-                    }
-
-                    if last_delta > prev_delta + 10.0 && prev_delta > curr_delta + 10.0 {
-                        // * previous increase happened a note ago, 1/1 -> 1/2-1/4, don't want to buff this
-                        effective_ratio *= 0.125;
-                    }
-
-                    rhythm_complexity_sum += (effective_ratio * start_ratio).sqrt()
-                        * curr_historical_decay
-                        * ((4 + island_size) as f64).sqrt()
-                        * ((4 + prev_island_size) as f64).sqrt()
-                        / 4.0;
-
-                    start_ratio = effective_ratio;
-                    prev_island_size = island_size;
-                    island_size = 1;
-
-                    // * we're slowing down, stop counting
-                    if prev_delta * 1.25 < curr_delta {
-                        // * if we're speeding up, this stays true and we keep counting island size
-                        first_delta_switch = false;
-                    }
-                }
-            } else if prev_delta > 1.25 * curr_delta {
-                // * we want to be speeding up
-                // * begin counting island until we change speed again
-                first_delta_switch = true;
-                start_ratio = effective_ratio;
-                island_size = 1;
-            }
-        }
-    }
-
-    // * produces multiplier that can be applied to strain. range [1, infinity) (not really though)
-    (4.0 + rhythm_complexity_sum * SPEED_RHYTHM_MULTIPLIER).sqrt() / 2.0
-}
-
-fn calculate_wide_angle_bonus(angle: f64) -> f64 {
-    let base = (3.0 / 4.0 * ((PI / 6.0).max(angle).min(5.0 / 6.0 * PI) - PI / 6.0)).sin();
-
-    base * base
-}
-
-fn calculate_acute_angle_bonus(angle: f64) -> f64 {
-    1.0 - calculate_wide_angle_bonus(angle)
-}
-
-impl fmt::Debug for SkillKind {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self {
-            Self::Aim { .. } => f.debug_struct("Aim").finish(),
-            Self::Flashlight { .. } => f.debug_struct("Flashlight").finish(),
-            Self::Speed { .. } => f.debug_struct("Speed").finish(),
-        }
-    }
-}

src/osu/skills/aim.rs

@@ -0,0 +1,273 @@
+use std::{
+    any::Any,
+    f64::consts::{FRAC_PI_2, FRAC_PI_6, PI},
+    mem,
+};
+
+use crate::osu::difficulty_object::OsuDifficultyObject;
+
+use super::{previous, previous_start_time, OsuStrainSkill, Skill, StrainSkill};
+
+#[derive(Clone)]
+pub(crate) struct Aim {
+    curr_strain: f64,
+    curr_section_peak: f64,
+    curr_section_end: f64,
+    strain_peaks: Vec<f64>,
+    with_sliders: bool,
+}
+
+impl Aim {
+    const SKILL_MULTIPLIER: f64 = 23.55;
+    const STRAIN_DECAY_BASE: f64 = 0.15;
+
+    pub(crate) fn new(with_sliders: bool) -> Self {
+        Self {
+            curr_strain: 0.0,
+            curr_section_peak: 0.0,
+            curr_section_end: 0.0,
+            strain_peaks: Vec::new(),
+            with_sliders,
+        }
+    }
+
+    fn strain_decay(ms: f64) -> f64 {
+        Self::STRAIN_DECAY_BASE.powf(ms / 1000.0)
+    }
+}
+
+impl Skill for Aim {
+    fn process(
+        &mut self,
+        curr: &OsuDifficultyObject<'_>,
+        diff_objects: &[OsuDifficultyObject<'_>],
+        hit_window: f64,
+    ) {
+        <Self as StrainSkill>::process(self, curr, diff_objects, hit_window)
+    }
+
+    fn difficulty_value(&mut self) -> f64 {
+        <Self as OsuStrainSkill>::difficulty_value(self)
+    }
+
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+
+    fn as_any_mut(&mut self) -> &mut dyn Any {
+        self
+    }
+
+    fn take_strain_peaks(&mut self) -> Vec<f64> {
+        mem::take(&mut self.strain_peaks)
+    }
+}
+
+impl StrainSkill for Aim {
+    fn strain_peaks_mut(&mut self) -> &mut Vec<f64> {
+        &mut self.strain_peaks
+    }
+
+    fn curr_section_peak(&mut self) -> &mut f64 {
+        &mut self.curr_section_peak
+    }
+
+    fn curr_section_end(&mut self) -> &mut f64 {
+        &mut self.curr_section_end
+    }
+
+    fn strain_value_at(
+        &mut self,
+        curr: &OsuDifficultyObject<'_>,
+        diff_objects: &[OsuDifficultyObject<'_>],
+        _hit_window: f64,
+    ) -> f64 {
+        self.curr_strain *= Self::strain_decay(curr.delta_time);
+        self.curr_strain += AimEvaluator::evaluate_diff_of(curr, diff_objects, self.with_sliders)
+            * Self::SKILL_MULTIPLIER;
+
+        self.curr_strain
+    }
+
+    fn calculate_initial_strain(
+        &self,
+        time: f64,
+        curr: &OsuDifficultyObject<'_>,
+        diff_objects: &[OsuDifficultyObject<'_>],
+    ) -> f64 {
+        self.curr_strain * Self::strain_decay(time - previous_start_time(diff_objects, curr.idx, 0))
+    }
+
+    fn difficulty_value(&mut self) -> f64 {
+        <Self as OsuStrainSkill>::difficulty_value(self)
+    }
+}
+
+impl OsuStrainSkill for Aim {}
+
+struct AimEvaluator;
+
+impl AimEvaluator {
+    const WIDE_ANGLE_MULTIPLIER: f64 = 1.5;
+    const ACUTE_ANGLE_MULTIPLIER: f64 = 1.95;
+    const SLIDER_MULTIPLIER: f64 = 1.35;
+    const VELOCITY_CHANGE_MULTIPLIER: f64 = 0.75;
+
+    fn evaluate_diff_of(
+        curr: &OsuDifficultyObject<'_>,
+        diff_objects: &[OsuDifficultyObject<'_>],
+        with_sliders: bool,
+    ) -> f64 {
+        let osu_curr_obj = curr;
+
+        let (osu_last_last_obj, osu_last_obj) = if let Some(tuple) =
+            previous(diff_objects, curr.idx, 1)
+                .zip(previous(diff_objects, curr.idx, 0))
+                .filter(|(_, last)| !(curr.base.is_spinner() || last.base.is_spinner()))
+        {
+            tuple
+        } else {
+            return 0.0;
+        };
+
+        // * Calculate the velocity to the current hitobject, which starts
+        // * with a base distance / time assuming the last object is a hitcircle.
+        let mut curr_vel = osu_curr_obj.dists.lazy_jump_dist / osu_curr_obj.strain_time;
+
+        // * But if the last object is a slider, then we extend the travel
+        // * velocity through the slider into the current object.
+        if osu_last_obj.base.is_slider() && with_sliders {
+            // * calculate the slider velocity from slider head to slider end.
+            let travel_vel = osu_last_obj.dists.travel_dist / osu_last_obj.dists.travel_time;
+            // * calculate the movement velocity from slider end to current object
+            let movement_vel = osu_curr_obj.dists.min_jump_dist / osu_curr_obj.dists.min_jump_time;
+
+            // * take the larger total combined velocity.
+            curr_vel = curr_vel.max(movement_vel + travel_vel);
+        }
+
+        // * As above, do the same for the previous hitobject.
+        let mut prev_vel = osu_last_obj.dists.lazy_jump_dist / osu_last_obj.strain_time;
+
+        if osu_last_last_obj.base.is_slider() && with_sliders {
+            let travel_vel =
+                osu_last_last_obj.dists.travel_dist / osu_last_last_obj.dists.travel_time;
+            let movement_vel = osu_last_obj.dists.min_jump_dist / osu_last_obj.dists.min_jump_time;
+
+            prev_vel = prev_vel.max(movement_vel + travel_vel);
+        }
+
+        let mut wide_angle_bonus = 0.0;
+        let mut acute_angle_bonus = 0.0;
+        let mut slider_bonus = 0.0;
+        let mut vel_change_bonus = 0.0;
+
+        // * Start strain with regular velocity.
+        let mut aim_strain = curr_vel;
+
+        // * If rhythms are the same.
+        if osu_curr_obj.strain_time.max(osu_last_obj.strain_time)
+            < 1.25 * osu_curr_obj.strain_time.min(osu_last_obj.strain_time)
+        {
+            if let Some(((curr_angle, last_angle), last_last_angle)) = osu_curr_obj
+                .dists
+                .angle
+                .zip(osu_last_obj.dists.angle)
+                .zip(osu_last_last_obj.dists.angle)
+            {
+                // * Rewarding angles, take the smaller velocity as base.
+                let angle_bonus = curr_vel.min(prev_vel);
+
+                wide_angle_bonus = Self::calc_wide_angle_bonus(curr_angle);
+                acute_angle_bonus = Self::calc_acute_angle_bonus(curr_angle);
+
+                // * Only buff deltaTime exceeding 300 bpm 1/2.
+                if osu_curr_obj.strain_time > 100.0 {
+                    acute_angle_bonus = 0.0;
+                } else {
+                    let base1 =
+                        (FRAC_PI_2 * ((100.0 - osu_curr_obj.strain_time) / 25.0).min(1.0)).sin();
+
+                    let base2 = (FRAC_PI_2
+                        * ((osu_curr_obj.dists.lazy_jump_dist).clamp(50.0, 100.0) - 50.0)
+                        / 50.0)
+                        .sin();
+
+                    // * Multiply by previous angle, we don't want to buff unless this is a wiggle type pattern.
+                    acute_angle_bonus *= Self::calc_acute_angle_bonus(last_angle)
+                    // * The maximum velocity we buff is equal to 125 / strainTime
+                        * angle_bonus.min(125.0 / osu_curr_obj.strain_time)
+                        // * scale buff from 150 bpm 1/4 to 200 bpm 1/4
+                        * base1
+                        * base1
+                         // * Buff distance exceeding 50 (radius) up to 100 (diameter).
+                        * base2
+                        * base2;
+                }
+
+                // * Penalize wide angles if they're repeated, reducing the penalty as the lastAngle gets more acute.
+                wide_angle_bonus *= angle_bonus
+                    * (1.0 - wide_angle_bonus.min(Self::calc_wide_angle_bonus(last_angle).powi(3)));
+                // * Penalize acute angles if they're repeated, reducing the penalty as the lastLastAngle gets more obtuse.
+                acute_angle_bonus *= 0.5
+                    + 0.5
+                        * (1.0
+                            - acute_angle_bonus
+                                .min(Self::calc_acute_angle_bonus(last_last_angle).powi(3)));
+            }
+        }
+
+        if prev_vel.max(curr_vel).abs() > f64::EPSILON {
+            // * We want to use the average velocity over the whole object when awarding
+            // * differences, not the individual jump and slider path velocities.
+            prev_vel = (osu_last_obj.dists.lazy_jump_dist + osu_last_last_obj.dists.travel_dist)
+                / osu_last_obj.strain_time;
+            curr_vel = (osu_curr_obj.dists.lazy_jump_dist + osu_last_obj.dists.travel_dist)
+                / osu_curr_obj.strain_time;
+
+            // * Scale with ratio of difference compared to 0.5 * max dist.
+            let dist_ratio_base =
+                (FRAC_PI_2 * (prev_vel - curr_vel).abs() / prev_vel.max(curr_vel)).sin();
+            let dist_ratio = dist_ratio_base * dist_ratio_base;
+
+            // * Reward for % distance up to 125 / strainTime for overlaps where velocity is still changing.
+            let overlap_vel_buff = (125.0 / osu_curr_obj.strain_time.min(osu_last_obj.strain_time))
+                .min((prev_vel - curr_vel).abs());
+
+            vel_change_bonus = overlap_vel_buff * dist_ratio;
+
+            // * Penalize for rhythm changes.
+            let bonus_base = (osu_curr_obj.strain_time).min(osu_last_obj.strain_time)
+                / (osu_curr_obj.strain_time).max(osu_last_obj.strain_time);
+            vel_change_bonus *= bonus_base * bonus_base;
+        }
+
+        if osu_last_obj.base.is_slider() {
+            // * Reward sliders based on velocity.
+            slider_bonus = osu_last_obj.dists.travel_dist / osu_last_obj.dists.travel_time
+        }
+
+        // * Add in acute angle bonus or wide angle bonus + velocity change bonus, whichever is larger.
+        aim_strain += (acute_angle_bonus * Self::ACUTE_ANGLE_MULTIPLIER).max(
+            wide_angle_bonus * Self::WIDE_ANGLE_MULTIPLIER
+                + vel_change_bonus * Self::VELOCITY_CHANGE_MULTIPLIER,
+        );
+
+        // * Add in additional slider velocity bonus.
+        if with_sliders {
+            aim_strain += slider_bonus * Self::SLIDER_MULTIPLIER;
+        }
+
+        aim_strain
+    }
+
+    fn calc_wide_angle_bonus(angle: f64) -> f64 {
+        let base = (3.0 / 4.0 * ((5.0 / 6.0 * PI).min(angle.max(FRAC_PI_6)) - FRAC_PI_6)).sin();
+
+        base * base
+    }
+
+    fn calc_acute_angle_bonus(angle: f64) -> f64 {
+        1.0 - Self::calc_wide_angle_bonus(angle)
+    }
+}

src/osu/skills/flashlight.rs

@@ -0,0 +1,235 @@
+use std::{any::Any, mem};
+
+use crate::{
+    osu::{
+        difficulty_object::OsuDifficultyObject,
+        osu_object::{NestedObjectKind, OsuObjectKind},
+    },
+    Mods,
+};
+
+use super::{previous, previous_start_time, OsuStrainSkill, Skill, StrainSkill};
+
+#[derive(Clone)]
+pub(crate) struct Flashlight {
+    curr_strain: f64,
+    curr_section_peak: f64,
+    curr_section_end: f64,
+    strain_peaks: Vec<f64>,
+    has_hidden_mod: bool,
+    scaling_factor: f64,
+}
+
+impl Flashlight {
+    const SKILL_MULTIPLIER: f64 = 0.052;
+    const STRAIN_DECAY_BASE: f64 = 0.15;
+
+    pub(crate) fn new(mods: u32, radius: f32) -> Self {
+        Self {
+            curr_strain: 0.0,
+            curr_section_peak: 0.0,
+            curr_section_end: 0.0,
+            strain_peaks: Vec::new(),
+            has_hidden_mod: mods.hd(),
+            scaling_factor: 52.0 / radius as f64,
+        }
+    }
+
+    fn strain_decay(ms: f64) -> f64 {
+        Self::STRAIN_DECAY_BASE.powf(ms / 1000.0)
+    }
+}
+
+impl Skill for Flashlight {
+    fn process(
+        &mut self,
+        curr: &OsuDifficultyObject<'_>,
+        diff_objects: &[OsuDifficultyObject<'_>],
+        hit_window: f64,
+    ) {
+        <Self as StrainSkill>::process(self, curr, diff_objects, hit_window)
+    }
+
+    fn difficulty_value(&mut self) -> f64 {
+        <Self as StrainSkill>::difficulty_value(self)
+    }
+
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+
+    fn as_any_mut(&mut self) -> &mut dyn Any {
+        self
+    }
+
+    fn take_strain_peaks(&mut self) -> Vec<f64> {
+        mem::take(&mut self.strain_peaks)
+    }
+}
+
+impl StrainSkill for Flashlight {
+    const DECAY_WEIGHT: f64 = 0.9;
+
+    fn strain_peaks_mut(&mut self) -> &mut Vec<f64> {
+        &mut self.strain_peaks
+    }
+
+    fn curr_section_peak(&mut self) -> &mut f64 {
+        &mut self.curr_section_peak
+    }
+
+    fn curr_section_end(&mut self) -> &mut f64 {
+        &mut self.curr_section_end
+    }
+
+    fn strain_value_at(
+        &mut self,
+        curr: &OsuDifficultyObject<'_>,
+        diff_objects: &[OsuDifficultyObject<'_>],
+        _hit_window: f64,
+    ) -> f64 {
+        self.curr_strain *= Self::strain_decay(curr.delta_time);
+        self.curr_strain += FlashlightEvaluator::evaluate_diff_of(
+            curr,
+            diff_objects,
+            self.has_hidden_mod,
+            self.scaling_factor,
+        ) * Self::SKILL_MULTIPLIER;
+
+        self.curr_strain
+    }
+
+    fn calculate_initial_strain(
+        &self,
+        time: f64,
+        curr: &OsuDifficultyObject<'_>,
+        diff_objects: &[OsuDifficultyObject<'_>],
+    ) -> f64 {
+        self.curr_strain * Self::strain_decay(time - previous_start_time(diff_objects, curr.idx, 0))
+    }
+
+    fn difficulty_value(&mut self) -> f64 {
+        self.get_curr_strain_peaks().into_iter().sum::<f64>() * Self::DIFFICULTY_MULTIPLER
+    }
+}
+
+impl OsuStrainSkill for Flashlight {}
+
+struct FlashlightEvaluator;
+
+impl FlashlightEvaluator {
+    const MAX_OPACITY_BONUS: f64 = 0.4;
+    const HIDDEN_BONUS: f64 = 0.2;
+
+    const MIN_VELOCITY: f64 = 0.5;
+    const SLIDER_MULTIPLIER: f64 = 1.3;
+
+    const MIN_ANGLE_MULTIPLIER: f64 = 0.2;
+
+    fn evaluate_diff_of(
+        curr: &OsuDifficultyObject<'_>,
+        diff_objects: &[OsuDifficultyObject<'_>],
+        hidden: bool,
+        scaling_factor: f64,
+    ) -> f64 {
+        if curr.base.is_spinner() {
+            return 0.0;
+        }
+
+        let osu_curr = curr;
+        let osu_hit_obj = curr.base;
+
+        let mut small_dist_nerf = 1.0;
+        let mut cumulative_strain_time = 0.0;
+
+        let mut result = 0.0;
+
+        let mut last_obj = osu_curr;
+
+        let mut angle_repeat_count = 0.0;
+
+        // * This is iterating backwards in time from the current object.
+        for i in 0..curr.idx.min(10) {
+            let curr_obj = if let Some(curr_obj) = previous(diff_objects, curr.idx, i) {
+                curr_obj
+            } else {
+                break;
+            };
+
+            let curr_hit_obj = curr_obj.base;
+
+            if !curr_obj.base.is_spinner() {
+                let jump_dist = (osu_hit_obj.pos - curr_hit_obj.end_pos()).length() as f64;
+                cumulative_strain_time += last_obj.strain_time;
+
+                // * We want to nerf objects that can be easily seen within the Flashlight circle radius.
+                if i == 0 {
+                    small_dist_nerf = (jump_dist / 75.0).min(1.0);
+                }
+
+                // * We also want to nerf stacks so that only the first object of the stack is accounted for.
+                let stack_nerf = ((curr_obj.dists.lazy_jump_dist / scaling_factor) / 25.0).min(1.0);
+
+                // * Bonus based on how visible the object is.
+                let opacity_bonus = 1.0
+                    + Self::MAX_OPACITY_BONUS
+                        * (1.0 - osu_curr.opacity_at(curr_hit_obj.start_time, hidden));
+
+                result += stack_nerf * opacity_bonus * scaling_factor * jump_dist
+                    / cumulative_strain_time;
+
+                if let Some((curr_obj_angle, osu_curr_angle)) =
+                    curr_obj.dists.angle.zip(osu_curr.dists.angle)
+                {
+                    // * Objects further back in time should count less for the nerf.
+                    if (curr_obj_angle - osu_curr_angle).abs() < 0.02 {
+                        angle_repeat_count += (1.0 - 0.1 * i as f64).max(0.0);
+                    }
+                }
+            }
+
+            last_obj = curr_obj;
+        }
+
+        let base = small_dist_nerf * result;
+        result = base * base;
+
+        // * Additional bonus for Hidden due to there being no approach circles.
+        if hidden {
+            result *= 1.0 + Self::HIDDEN_BONUS;
+        }
+
+        // * Nerf patterns with repeated angles.
+        result *= Self::MIN_ANGLE_MULTIPLIER
+            + (1.0 - Self::MIN_ANGLE_MULTIPLIER) / (angle_repeat_count + 1.0);
+
+        let mut slider_bonus = 0.0;
+
+        if let OsuObjectKind::Slider { nested_objects, .. } = &osu_curr.base.kind {
+            // * Invert the scaling factor to determine the true travel distance independent of circle size.
+            let pixel_travel_dist = osu_curr.dists.lazy_travel_dist as f64 / scaling_factor;
+
+            // * Reward sliders based on velocity.
+            slider_bonus = ((pixel_travel_dist / osu_curr.dists.travel_time as f64
+                - Self::MIN_VELOCITY)
+                .max(0.0))
+            .sqrt();
+
+            // * Longer sliders require more memorisation.
+            slider_bonus *= pixel_travel_dist;
+
+            // * Nerf sliders with repeats, as less memorisation is required.
+            let repeat_count = nested_objects.iter().fold(0, |count, nested| {
+                count + matches!(nested.kind, NestedObjectKind::Repeat) as usize
+            });
+
+            if repeat_count > 0 {
+                slider_bonus /= (repeat_count + 1) as f64;
+            }
+        }
+
+        result += slider_bonus * Self::SLIDER_MULTIPLIER;
+
+        result
+    }
+}

src/osu/skills/mod.rs

@@ -0,0 +1,166 @@
+mod aim;
+mod flashlight;
+mod speed;
+
+use std::{any::Any, cmp::Ordering, mem};
+
+pub(crate) use self::{aim::Aim, flashlight::Flashlight, speed::Speed};
+
+use super::{difficulty_object::OsuDifficultyObject, SECTION_LEN};
+
+pub(crate) trait Skill {
+    fn process(
+        &mut self,
+        curr: &OsuDifficultyObject<'_>,
+        diff_objects: &[OsuDifficultyObject<'_>],
+        hit_window: f64,
+    );
+    fn difficulty_value(&mut self) -> f64;
+    fn as_any(&self) -> &dyn Any;
+    fn as_any_mut(&mut self) -> &mut dyn Any;
+    fn take_strain_peaks(&mut self) -> Vec<f64>;
+}
+
+pub(crate) trait StrainSkill: Skill + Sized {
+    const DECAY_WEIGHT: f64 = 0.9;
+
+    fn strain_peaks_mut(&mut self) -> &mut Vec<f64>;
+    fn curr_section_peak(&mut self) -> &mut f64;
+    fn curr_section_end(&mut self) -> &mut f64;
+
+    fn strain_value_at(
+        &mut self,
+        curr: &OsuDifficultyObject<'_>,
+        diff_objects: &[OsuDifficultyObject<'_>],
+        hit_window: f64,
+    ) -> f64;
+
+    fn calculate_initial_strain(
+        &self,
+        time: f64,
+        curr: &OsuDifficultyObject<'_>,
+        diff_objects: &[OsuDifficultyObject<'_>],
+    ) -> f64;
+
+    fn process(
+        &mut self,
+        curr: &OsuDifficultyObject<'_>,
+        diff_objects: &[OsuDifficultyObject<'_>],
+        hit_window: f64,
+    ) {
+        // * The first object doesn't generate a strain, so we begin with an incremented section end
+        if curr.idx == 0 {
+            let section_len = SECTION_LEN as f64;
+            *self.curr_section_end() = (curr.start_time / section_len).ceil() * section_len;
+        }
+
+        while curr.start_time > *self.curr_section_end() {
+            self.save_curr_peak();
+
+            {
+                let section_end = *self.curr_section_end();
+                self.start_new_section_from(section_end, curr, diff_objects);
+            }
+
+            *self.curr_section_end() += SECTION_LEN as f64;
+        }
+
+        *self.curr_section_peak() = self
+            .strain_value_at(curr, diff_objects, hit_window)
+            .max(*self.curr_section_peak());
+    }
+
+    fn save_curr_peak(&mut self) {
+        let peak = *self.curr_section_peak();
+        self.strain_peaks_mut().push(peak);
+    }
+
+    fn start_new_section_from(
+        &mut self,
+        time: f64,
+        curr: &OsuDifficultyObject<'_>,
+        diff_objects: &[OsuDifficultyObject<'_>],
+    ) {
+        // * The maximum strain of the new section is not zero by default
+        // * This means we need to capture the strain level at the beginning of the new section,
+        // * and use that as the initial peak level.
+        *self.curr_section_peak() = self.calculate_initial_strain(time, curr, diff_objects);
+    }
+
+    fn difficulty_value(&mut self) -> f64;
+
+    fn get_curr_strain_peaks(&mut self) -> Vec<f64> {
+        let curr_peak = *self.curr_section_peak();
+        let mut strain_peaks = mem::take(self.strain_peaks_mut());
+        strain_peaks.push(curr_peak);
+
+        strain_peaks
+    }
+}
+
+pub(crate) trait OsuStrainSkill: StrainSkill + Sized {
+    const REDUCED_SECTION_COUNT: usize = 10;
+    const REDUCED_STRAIN_BASELINE: f64 = 0.75;
+    const DIFFICULTY_MULTIPLER: f64 = 1.06;
+
+    fn difficulty_value(&mut self) -> f64 {
+        let mut difficulty = 0.0;
+        let mut weight = 1.0;
+
+        // * Sections with 0 strain are excluded to avoid worst-case time complexity of the following sort (e.g. /b/2351871).
+        // * These sections will not contribute to the difficulty.
+        let mut peaks = self.get_curr_strain_peaks();
+
+        peaks.retain(|&peak| peak > 0.0);
+        peaks.sort_unstable_by(|a, b| b.partial_cmp(a).unwrap_or(Ordering::Equal));
+
+        let peak_iter = peaks.iter_mut().take(Self::REDUCED_SECTION_COUNT);
+
+        fn lerp(start: f64, end: f64, amount: f64) -> f64 {
+            start + (end - start) * amount
+        }
+
+        // * We are reducing the highest strains first to account for extreme difficulty spikes
+        for (i, strain) in peak_iter.enumerate() {
+            let clamped = (i as f32 / Self::REDUCED_SECTION_COUNT as f32).clamp(0.0, 1.0) as f64;
+            let scale = (lerp(1.0, 10.0, clamped)).log10();
+            *strain *= lerp(Self::REDUCED_STRAIN_BASELINE, 1.0, scale);
+        }
+
+        peaks.sort_unstable_by(|a, b| b.partial_cmp(a).unwrap_or(Ordering::Equal));
+
+        // * Difficulty is the weighted sum of the highest strains from every section.
+        // * We're sorting from highest to lowest strain.
+        for strain in peaks {
+            difficulty += strain * weight;
+            weight *= Self::DECAY_WEIGHT;
+        }
+
+        difficulty * Self::DIFFICULTY_MULTIPLER
+    }
+}
+
+fn previous<'map, 'objects>(
+    diff_objects: &'objects [OsuDifficultyObject<'map>],
+    curr: usize,
+    backwards_idx: usize,
+) -> Option<&'objects OsuDifficultyObject<'map>> {
+    curr.checked_sub(backwards_idx + 1)
+        .and_then(|idx| diff_objects.get(idx))
+}
+
+fn previous_start_time(
+    diff_objects: &[OsuDifficultyObject<'_>],
+    curr: usize,
+    backwards_idx: usize,
+) -> f64 {
+    previous(diff_objects, curr, backwards_idx).map_or(0.0, |h| h.start_time)
+}
+
+fn next<'map, 'objects>(
+    diff_objects: &'objects [OsuDifficultyObject<'map>],
+    curr: usize,
+    forwards_idx: usize,
+) -> Option<&'objects OsuDifficultyObject<'map>> {
+    diff_objects.get(curr + (forwards_idx + 1))
+}

src/osu/skills/speed.rs

@@ -0,0 +1,331 @@
+use std::{any::Any, cmp::Ordering, f64::consts::PI, mem};
+
+use crate::osu::difficulty_object::OsuDifficultyObject;
+
+use super::{next, previous, previous_start_time, OsuStrainSkill, Skill, StrainSkill};
+
+#[derive(Clone)]
+pub(crate) struct Speed {
+    curr_strain: f64,
+    curr_section_peak: f64,
+    curr_section_end: f64,
+    curr_rhythm: f64,
+    strain_peaks: Vec<f64>,
+    object_strains: Vec<f64>,
+}
+
+impl Speed {
+    const SKILL_MULTIPLIER: f64 = 1375.0;
+    const STRAIN_DECAY_BASE: f64 = 0.3;
+
+    pub(crate) fn new() -> Self {
+        Self {
+            curr_strain: 0.0,
+            curr_section_peak: 0.0,
+            curr_section_end: 0.0,
+            curr_rhythm: 0.0,
+            strain_peaks: Vec::new(),
+            object_strains: Vec::new(),
+        }
+    }
+
+    fn strain_decay(ms: f64) -> f64 {
+        Self::STRAIN_DECAY_BASE.powf(ms / 1000.0)
+    }
+
+    pub(crate) fn relevant_note_count(&self) -> f64 {
+        self.object_strains
+            .iter()
+            .max_by(|a, b| a.partial_cmp(b).unwrap_or(Ordering::Equal))
+            .copied()
+            .filter(|&n| n > 0.0)
+            .map_or(0.0, |max_strain| {
+                self.object_strains.iter().fold(0.0, |sum, strain| {
+                    sum + (1.0 + (-(strain / max_strain * 12.0 - 6.0)).exp()).recip()
+                })
+            })
+    }
+}
+
+impl Skill for Speed {
+    fn process(
+        &mut self,
+        curr: &OsuDifficultyObject<'_>,
+        diff_objects: &[OsuDifficultyObject<'_>],
+        hit_window: f64,
+    ) {
+        <Self as StrainSkill>::process(self, curr, diff_objects, hit_window)
+    }
+
+    fn difficulty_value(&mut self) -> f64 {
+        <Self as OsuStrainSkill>::difficulty_value(self)
+    }
+
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+
+    fn as_any_mut(&mut self) -> &mut dyn Any {
+        self
+    }
+
+    fn take_strain_peaks(&mut self) -> Vec<f64> {
+        mem::take(&mut self.strain_peaks)
+    }
+}
+
+impl StrainSkill for Speed {
+    fn strain_peaks_mut(&mut self) -> &mut Vec<f64> {
+        &mut self.strain_peaks
+    }
+
+    fn curr_section_peak(&mut self) -> &mut f64 {
+        &mut self.curr_section_peak
+    }
+
+    fn curr_section_end(&mut self) -> &mut f64 {
+        &mut self.curr_section_end
+    }
+
+    fn strain_value_at(
+        &mut self,
+        curr: &OsuDifficultyObject<'_>,
+        diff_objects: &[OsuDifficultyObject<'_>],
+        hit_window: f64,
+    ) -> f64 {
+        self.curr_strain *= Self::strain_decay(curr.strain_time);
+        self.curr_strain += SpeedEvaluator::evaluate_diff_of(curr, diff_objects, hit_window)
+            * Self::SKILL_MULTIPLIER;
+        self.curr_rhythm = RhythmEvaluator::evaluate_diff_of(curr, diff_objects, hit_window);
+
+        let total_strain = self.curr_strain * self.curr_rhythm;
+        self.object_strains.push(total_strain);
+
+        total_strain
+    }
+
+    fn calculate_initial_strain(
+        &self,
+        time: f64,
+        curr: &OsuDifficultyObject<'_>,
+        diff_objects: &[OsuDifficultyObject<'_>],
+    ) -> f64 {
+        (self.curr_strain * self.curr_rhythm)
+            * Self::strain_decay(time - previous_start_time(diff_objects, curr.idx, 0))
+    }
+
+    fn difficulty_value(&mut self) -> f64 {
+        <Self as OsuStrainSkill>::difficulty_value(self)
+    }
+}
+
+impl OsuStrainSkill for Speed {
+    const REDUCED_SECTION_COUNT: usize = 5;
+    const DIFFICULTY_MULTIPLER: f64 = 1.04;
+}
+
+struct SpeedEvaluator;
+
+impl SpeedEvaluator {
+    const SINGLE_SPACING_THRESHOLD: f64 = 125.0;
+    const MIN_SPEED_BONUS: f64 = 75.0; // ~200BPM
+    const SPEED_BALANCING_FACTOR: f64 = 40.;
+
+    fn evaluate_diff_of(
+        curr: &OsuDifficultyObject<'_>,
+        diff_objects: &[OsuDifficultyObject<'_>],
+        hit_window: f64,
+    ) -> f64 {
+        if curr.base.is_spinner() {
+            return 0.0;
+        }
+
+        // * derive strainTime for calculation
+        let osu_curr_obj = curr;
+        let osu_prev_obj = previous(diff_objects, curr.idx, 0);
+        let osu_next_obj = next(diff_objects, curr.idx, 0);
+
+        let mut strain_time = curr.strain_time;
+        let mut doubletapness = 1.0;
+
+        // * Nerf doubletappable doubles.
+        if let Some(osu_next_obj) = osu_next_obj {
+            let curr_delta_time = osu_curr_obj.delta_time.max(1.0);
+            let next_delta_time = osu_next_obj.delta_time.max(1.0);
+            let delta_diff = (next_delta_time - curr_delta_time).abs();
+            let speed_ratio = curr_delta_time / curr_delta_time.max(delta_diff);
+            let window_ratio_base = (curr_delta_time / hit_window).min(1.0);
+            let window_ratio = window_ratio_base * window_ratio_base;
+            doubletapness = speed_ratio.powf(1.0 - window_ratio);
+        }
+
+        // * Cap deltatime to the OD 300 hitwindow.
+        // * 0.93 is derived from making sure 260bpm OD8 streams aren't nerfed harshly, whilst 0.92 limits the effect of the cap.
+        strain_time /= ((strain_time / hit_window) / 0.93).clamp(0.92, 1.0);
+
+        // * derive speedBonus for calculation
+        let speed_bonus = if strain_time < Self::MIN_SPEED_BONUS {
+            let base = (Self::MIN_SPEED_BONUS - strain_time) / Self::SPEED_BALANCING_FACTOR;
+
+            1.0 + 0.75 * base * base
+        } else {
+            1.0
+        };
+
+        let travel_dist = osu_prev_obj.map_or(0.0, |obj| obj.dists.travel_dist);
+        let dist =
+            Self::SINGLE_SPACING_THRESHOLD.min(travel_dist + osu_curr_obj.dists.min_jump_dist);
+
+        (speed_bonus + speed_bonus * (dist / Self::SINGLE_SPACING_THRESHOLD).powf(3.5))
+            * doubletapness
+            / strain_time
+    }
+}
+
+struct RhythmEvaluator;
+
+impl RhythmEvaluator {
+    // * 5 seconds of calculatingRhythmBonus max.
+    const HISTORY_TIME_MAX: u32 = 5000;
+    const RHYTHM_MULTIPLIER: f64 = 0.75;
+
+    fn evaluate_diff_of(
+        curr: &OsuDifficultyObject<'_>,
+        diff_objects: &[OsuDifficultyObject<'_>],
+        hit_window: f64,
+    ) -> f64 {
+        if curr.base.is_spinner() {
+            return 0.0;
+        }
+
+        let mut prev_island_size = 0;
+
+        let mut rhythm_complexity_sum = 0.0;
+        let mut island_size = 1;
+        // * store the ratio of the current start of an island to buff for tighter rhythms
+        let mut start_ratio = 0.0;
+
+        let mut first_delta_switch = false;
+
+        let historical_note_count = curr.idx.min(32);
+
+        let mut rhythm_start = 0;
+
+        while previous(diff_objects, curr.idx, rhythm_start)
+            .filter(|prev| {
+                rhythm_start + 2 < historical_note_count
+                    && curr.start_time - prev.start_time < Self::HISTORY_TIME_MAX as f64
+            })
+            .is_some()
+        {
+            rhythm_start += 1;
+        }
+
+        for i in (1..=rhythm_start).rev() {
+            let (curr_obj, prev_obj, last_obj) = if let Some(((curr, prev), last)) =
+                previous(diff_objects, curr.idx, i - 1)
+                    .zip(previous(diff_objects, curr.idx, i))
+                    .zip(previous(diff_objects, curr.idx, i + 1))
+            {
+                (curr, prev, last)
+            } else {
+                break;
+            };
+
+            // * scales note 0 to 1 from history to now
+            let mut curr_historical_decay = (Self::HISTORY_TIME_MAX as f64
+                - (curr.start_time - curr_obj.start_time))
+                / Self::HISTORY_TIME_MAX as f64;
+
+            // * either we're limited by time or limited by object count.
+            curr_historical_decay = curr_historical_decay
+                .min((historical_note_count - i) as f64 / historical_note_count as f64);
+
+            let curr_delta = curr_obj.strain_time;
+            let prev_delta = prev_obj.strain_time;
+            let last_delta = last_obj.strain_time;
+
+            // * fancy function to calculate rhythmbonuses.
+            let base = (PI / (prev_delta.min(curr_delta) / prev_delta.max(curr_delta))).sin();
+            let curr_ratio = 1.0 + 6.0 * (base * base).min(0.5);
+
+            let mut window_penalty = ((((prev_delta - curr_delta).abs() - hit_window * 0.3)
+                .max(0.0))
+                / (hit_window * 0.3))
+                .min(1.0);
+
+            println!("window_penalty: prev={prev_delta} | curr={curr_delta} | window={hit_window} => {window_penalty}");
+
+            window_penalty = window_penalty.min(1.0);
+
+            let mut effective_ratio = window_penalty * curr_ratio;
+
+            if first_delta_switch {
+                if !(prev_delta > 1.25 * curr_delta || prev_delta * 1.25 < curr_delta) {
+                    if island_size < 7 {
+                        // * island is still progressing, count size.
+                        island_size += 1;
+                    }
+                } else {
+                    // * bpm change is into slider, this is easy acc window
+                    if curr_obj.base.is_slider() {
+                        effective_ratio *= 0.125;
+                    }
+
+                    // * bpm change was from a slider, this is easier typically than circle -> circle
+                    if prev_obj.base.is_slider() {
+                        effective_ratio *= 0.25;
+                    }
+
+                    // * repeated island size (ex: triplet -> triplet)
+                    if prev_island_size == island_size {
+                        effective_ratio *= 0.25;
+                    }
+
+                    // * repeated island polartiy (2 -> 4, 3 -> 5)
+                    if prev_island_size % 2 == island_size % 2 {
+                        effective_ratio *= 0.5;
+                    }
+
+                    // * previous increase happened a note ago, 1/1->1/2-1/4, dont want to buff this.
+                    if last_delta > prev_delta + 10.0 && prev_delta > curr_delta + 10.0 {
+                        effective_ratio *= 0.125;
+                    }
+
+                    rhythm_complexity_sum += (effective_ratio * start_ratio).sqrt()
+                        * curr_historical_decay
+                        * ((4 + island_size) as f64).sqrt()
+                        / 2.0
+                        * ((4 + prev_island_size) as f64).sqrt()
+                        / 2.0;
+
+                    start_ratio = effective_ratio;
+
+                    // * log the last island size.
+                    prev_island_size = island_size;
+
+                    // * we're slowing down, stop counting
+                    if prev_delta * 1.25 < curr_delta {
+                        // * if we're speeding up, this stays true and  we keep counting island size.
+                        first_delta_switch = false;
+                    }
+
+                    island_size = 1;
+                }
+            } else if prev_delta > 1.25 * curr_delta {
+                // * we want to be speeding up.
+                // * Begin counting island until we change speed again.
+                first_delta_switch = true;
+                start_ratio = effective_ratio;
+                island_size = 1;
+            }
+        }
+
+        // * produces multiplier that can be applied to strain. range [1, infinity) (not really though)
+        let res = (4.0 + rhythm_complexity_sum * Self::RHYTHM_MULTIPLIER).sqrt() / 2.0;
+
+        println!("res={res}");
+
+        res
+    }
+}

src/osu/slider_state.rs

@@ -1,99 +0,0 @@
-use crate::beatmap::{Beatmap, ControlPoint, ControlPointIter};
-
-pub(crate) struct SliderState<'p> {
-    control_points: ControlPointIter<'p>,
-    next: Option<ControlPoint>,
-    pub(crate) beat_len: f64,
-    pub(crate) slider_velocity: f64,
-}
-
-impl<'p> SliderState<'p> {
-    #[inline]
-    pub(crate) fn new(map: &'p Beatmap) -> Self {
-        let mut control_points = ControlPointIter::new(map);
-
-        let (beat_len, slider_velocity) = match control_points.next() {
-            Some(ControlPoint::Timing(point)) => (point.beat_len, 1.0),
-            Some(ControlPoint::Difficulty(point)) => (1000.0, point.speed_multiplier),
-            None => (1000.0, 1.0),
-        };
-
-        Self {
-            next: control_points.next(),
-            control_points,
-            beat_len,
-            slider_velocity,
-        }
-    }
-
-    #[inline]
-    pub(crate) fn update(&mut self, time: f64) {
-        while let Some(next) = self.next.as_ref().filter(|n| time >= n.time()) {
-            match next {
-                ControlPoint::Timing(point) => {
-                    self.beat_len = point.beat_len;
-                    self.slider_velocity = 1.0;
-                }
-                ControlPoint::Difficulty(point) => self.slider_velocity = point.speed_multiplier,
-            }
-
-            self.next = self.control_points.next();
-        }
-    }
-}
-
-#[cfg(test)]
-mod test {
-    use crate::beatmap::{Beatmap, DifficultyPoint, TimingPoint};
-
-    use super::SliderState;
-
-    #[test]
-    fn osu_slider_state() {
-        let map = Beatmap {
-            timing_points: vec![
-                TimingPoint {
-                    time: 1.0,
-                    beat_len: 10.0,
-                    kiai: false,
-                },
-                TimingPoint {
-                    time: 3.0,
-                    beat_len: 20.0,
-                    kiai: false,
-                },
-                TimingPoint {
-                    time: 4.0,
-                    beat_len: 30.0,
-                    kiai: false,
-                },
-            ],
-            difficulty_points: vec![
-                DifficultyPoint {
-                    time: 2.0,
-                    speed_multiplier: 15.0,
-                    kiai: false,
-                },
-                DifficultyPoint {
-                    time: 5.0,
-                    speed_multiplier: 45.0,
-                    kiai: false,
-                },
-            ],
-            ..Default::default()
-        };
-
-        let mut state = SliderState::new(&map);
-
-        state.update(2.0);
-        assert!((state.beat_len - 10.0).abs() <= f64::EPSILON);
-
-        state.update(3.0);
-        assert!((state.beat_len - 20.0).abs() <= f64::EPSILON);
-        assert!((state.slider_velocity - 1.0).abs() <= f64::EPSILON);
-
-        state.update(5.0);
-        assert!((state.beat_len - 30.0).abs() <= f64::EPSILON);
-        assert!((state.slider_velocity - 45.0).abs() <= f64::EPSILON);
-    }
-}

src/parse/error.rs

@@ -1,9 +1,4 @@
-use std::{
-    error::Error as StdError,
-    fmt,
-    io::Error as IoError,
-    num::{ParseFloatError, ParseIntError},
-};
+use std::{error::Error as StdError, fmt, io::Error as IoError, num::ParseFloatError};
 
 /// `Result<_, ParseError>`
 pub type ParseResult<T> = Result<T, ParseError>;
@@ -22,14 +17,10 @@ pub enum ParseError {
     InvalidCurvePoints,
     /// Expected a decimal number, got something else.
     InvalidDecimalNumber,
-    /// Expected an integer, got something else.
-    InvalidInteger,
     /// Failed to parse game mode.
     InvalidMode,
     /// Expected an additional field.
     MissingField(&'static str),
-    /// Reject maps with too many repeat points.
-    TooManyRepeats,
     /// Failed to recognized specified type for hitobjects.
     UnknownHitObjectKind,
 }
@@ -43,11 +34,9 @@ impl fmt::Display for ParseError {
             }
             Self::BadLine => f.write_str("line not in `Key:Value` pattern"),
             Self::InvalidCurvePoints => f.write_str("invalid curve point"),
-            Self::InvalidInteger => f.write_str("invalid integer"),
             Self::InvalidDecimalNumber => f.write_str("invalid float number"),
             Self::InvalidMode => f.write_str("invalid mode"),
             Self::MissingField(field) => write!(f, "missing field `{}`", field),
-            Self::TooManyRepeats => f.write_str("repeat count is way too high"),
             Self::UnknownHitObjectKind => f.write_str("unsupported hitobject kind"),
         }
     }
@@ -60,11 +49,9 @@ impl StdError for ParseError {
             Self::IncorrectFileHeader => None,
             Self::BadLine => None,
             Self::InvalidCurvePoints => None,
-            Self::InvalidInteger => None,
             Self::InvalidDecimalNumber => None,
             Self::InvalidMode => None,
             Self::MissingField(_) => None,
-            Self::TooManyRepeats => None,
             Self::UnknownHitObjectKind => None,
         }
     }
@@ -76,12 +63,6 @@ impl From<IoError> for ParseError {
     }
 }
 
-impl From<ParseIntError> for ParseError {
-    fn from(_: ParseIntError) -> Self {
-        Self::InvalidInteger
-    }
-}
-
 impl From<ParseFloatError> for ParseError {
     fn from(_: ParseFloatError) -> Self {
         Self::InvalidDecimalNumber

src/parse/hitobject.rs

@@ -69,7 +69,7 @@ pub enum HitObjectKind {
     /// A full slider object.
     Slider {
         /// Total length of the slider in pixels.
-        pixel_len: f64,
+        pixel_len: Option<f64>,
         /// The amount of repeat points of the slider.
         repeats: usize,
         /// The control points of the slider.

src/parse/mod.rs

@@ -14,7 +14,10 @@ pub use slider_parsing::*;
 use reader::FileReader;
 pub(crate) use sort::legacy_sort;
 
-use std::cmp::Ordering;
+use std::{
+    cmp::Ordering,
+    ops::{ControlFlow, Neg},
+};
 
 #[cfg(not(any(feature = "async_std", feature = "async_tokio")))]
 use std::{fs::File, io::Read};
@@ -44,18 +47,33 @@ impl<T> OptionExt<T> for Option<T> {
     }
 }
 
-trait FloatExt: Sized {
-    fn validate(self) -> Result<Self, ParseError>;
-}
+trait InRange: Sized + Copy + Neg<Output = Self> + PartialOrd {
+    const LIMIT: Self;
 
-impl FloatExt for f64 {
-    fn validate(self) -> Result<Self, ParseError> {
-        self.is_finite()
-            .then(|| self)
-            .ok_or(ParseError::InvalidDecimalNumber)
+    fn is_in_range(&self) -> bool {
+        (-Self::LIMIT..=Self::LIMIT).contains(self)
+    }
+
+    fn is_in_custom_range(&self, limit: Self) -> bool {
+        (-limit..=limit).contains(self)
     }
 }
 
+impl InRange for i32 {
+    const LIMIT: Self = i32::MAX;
+}
+
+impl InRange for f32 {
+    const LIMIT: Self = i32::MAX as f32;
+}
+
+impl InRange for f64 {
+    const LIMIT: Self = i32::MAX as f64;
+}
+
+const MAX_COORDINATE_VALUE: i32 = 131_072;
+const KIAI_FLAG: i32 = 1 << 0;
+
 macro_rules! section {
     ($map:ident, $func:ident, $reader:ident, $section:ident) => {{
         #[cfg(not(any(feature = "async_std", feature = "async_tokio")))]
@@ -201,14 +219,11 @@ macro_rules! parse_events_body {
 
 macro_rules! parse_timingpoints_body {
     ($self:ident, $reader:ident, $section:ident) => {{
-        let mut unsorted_timings = false;
-        let mut unsorted_difficulties = false;
-
-        let mut prev_diff = 0.0;
-        let mut prev_time = 0.0;
-
         let mut empty = true;
 
+        let mut pending_diff_points_time = 0.0;
+        let mut pending_diff_point = None;
+
         while next_line!($reader)? != 0 {
             if let Some(bytes) = $reader.get_section() {
                 *$section = Section::from_bytes(bytes);
@@ -219,65 +234,125 @@ macro_rules! parse_timingpoints_body {
             let line = $reader.get_line()?;
             let mut split = line.split(',');
 
-            let time = split
+            let time: f64 = split
                 .next()
                 .next_field("timing point time")?
                 .trim()
-                .parse::<f64>()?
-                .validate()?;
+                .parse()?;
 
+            if !time.is_in_range() {
+                continue;
+            }
+
+            // * beatLength is allowed to be NaN to handle an edge case in which
+            // * some beatmaps use NaN slider velocity to disable slider tick
+            // * generation (see LegacyDifficultyControlPoint).
             let beat_len: f64 = split.next().next_field("beat len")?.trim().parse()?;
-            let timing_change = split.nth(4).and_then(|value| value.bytes().next());
-            let effect_flags = split.next().and_then(|value| value.bytes().next());
 
-            let kiai = matches!(effect_flags, Some(b'1'));
+            if !(beat_len.is_in_range() || beat_len.is_nan()) {
+                continue;
+            }
 
-            if matches!(timing_change, Some(b'1') | None) {
-                let beat_len = beat_len.clamp(6.0, 60_000.0);
+            let mut timing_change = true;
+            let mut kiai = false;
 
+            enum Status {
+                Ok,
+                Err,
+            }
+
+            fn parse_remaining<'s, I>(
+                mut split: I,
+                timing_change: &mut bool,
+                kiai: &mut bool,
+            ) -> Status
+            where
+                I: Iterator<Item = &'s str>,
+            {
+                match split
+                    .next()
+                    .filter(|&sig| !sig.starts_with('0'))
+                    .map(str::parse::<i32>)
+                {
+                    Some(Ok(time_sig)) if !time_sig.is_in_range() || time_sig < 1 => {
+                        return Status::Err
+                    }
+                    Some(Ok(_)) => {}
+                    None => return Status::Ok,
+                    Some(Err(_)) => return Status::Err,
+                }
+
+                match split.next().map(str::parse::<i32>) {
+                    Some(Ok(sample_set)) if !sample_set.is_in_range() => return Status::Err,
+                    Some(Ok(_)) => {}
+                    None => return Status::Ok,
+                    Some(Err(_)) => return Status::Err,
+                }
+
+                match split.next().map(str::parse::<i32>) {
+                    Some(Ok(custom_sample)) if !custom_sample.is_in_range() => return Status::Err,
+                    Some(Ok(_)) => {}
+                    None => return Status::Ok,
+                    Some(Err(_)) => return Status::Err,
+                }
+
+                match split.next().map(str::parse::<i32>) {
+                    Some(Ok(sample_volume)) if !sample_volume.is_in_range() => return Status::Err,
+                    Some(Ok(_)) => {}
+                    None => return Status::Ok,
+                    Some(Err(_)) => return Status::Err,
+                }
+
+                if let Some(byte) = split.next().and_then(|value| value.bytes().next()) {
+                    *timing_change = byte == b'1';
+                } else {
+                    return Status::Ok;
+                }
+
+                match split.next().map(str::parse::<i32>) {
+                    Some(Ok(effect_flags)) if !effect_flags.is_in_range() => return Status::Err,
+                    Some(Ok(effect_flags)) => *kiai = (effect_flags & KIAI_FLAG) > 0,
+                    None => return Status::Ok,
+                    Some(Err(_)) => return Status::Err,
+                }
+
+                Status::Ok
+            }
+
+            if let Status::Err = parse_remaining(split, &mut timing_change, &mut kiai) {
+                continue;
+            }
+
+            if timing_change {
                 let point = TimingPoint {
                     time,
-                    beat_len,
+                    beat_len: beat_len.clamp(6.0, 60_000.0),
                     kiai,
                 };
 
                 $self.timing_points.push(point);
+            }
 
-                if time < prev_time {
-                    unsorted_timings = true;
-                } else {
-                    prev_time = time;
-                }
+            // * If beatLength is NaN, speedMultiplier should still be 1
+            // * because all comparisons against NaN are false.
+            let speed_multiplier = if beat_len < 0.0 {
+                (100.0 / -beat_len)
             } else {
-                let speed_multiplier = if beat_len < 0.0 {
-                    (-100.0 / beat_len).clamp(0.1, 10.0)
-                } else {
-                    1.0
-                };
+                1.0
+            };
 
-                let point = DifficultyPoint {
-                    time,
-                    speed_multiplier,
-                    kiai,
-                };
-
-                $self.difficulty_points.push(point);
-
-                if time < prev_diff {
-                    unsorted_difficulties = true;
-                } else {
-                    prev_diff = time;
+            if time != pending_diff_points_time {
+                if let Some(point) = pending_diff_point.take() {
+                    $self.difficulty_points.push_if_not_redundant(point);
                 }
             }
+
+            pending_diff_point = Some(DifficultyPoint::new(time, beat_len, speed_multiplier, kiai));
+            pending_diff_points_time = time;
         }
 
-        if unsorted_timings {
-            sort_unstable(&mut $self.timing_points);
-        }
-
-        if unsorted_difficulties {
-            sort_unstable(&mut $self.difficulty_points);
-        }
+        $self.timing_points.dedup_by_key(|point| point.time);
+        $self.difficulty_points.dedup_by_key(|point| point.time);
 
         Ok(empty)
     }};
@@ -308,24 +383,36 @@ macro_rules! parse_hitobjects_body {
             let line = $reader.get_line()?;
             let mut split = line.split(',');
 
-            let pos = Pos2 {
-                x: split.next().next_field("x pos")?.parse()?,
-                y: split.next().next_field("y pos")?.parse()?,
-            };
+            let x: f32 = split.next().next_field("x pos")?.parse()?;
+            let y: f32 = split.next().next_field("y pos")?.parse()?;
 
-            let time = split
-                .next()
-                .next_field("hitobject time")?
-                .trim()
-                .parse::<f64>()?
-                .validate()?;
+            if !(x.is_in_custom_range(MAX_COORDINATE_VALUE as f32)
+                && y.is_in_custom_range(MAX_COORDINATE_VALUE as f32))
+            {
+                continue;
+            }
+
+            let pos = Pos2 { x, y };
+
+            let time: f64 = split.next().next_field("hitobject time")?.trim().parse()?;
+
+            if !time.is_in_range() {
+                continue;
+            }
 
             if !$self.hit_objects.is_empty() && time < prev_time {
                 unsorted = true;
             }
 
-            let kind: u8 = split.next().next_field("hitobject kind")?.parse()?;
-            let sound = split.next().map(str::parse).transpose()?.unwrap_or(0);
+            let kind: u8 = match split.next().next_field("hitobject kind")?.parse() {
+                Ok(kind) => kind,
+                Err(_) => continue,
+            };
+
+            let sound: u8 = match split.next().next_field("sound")?.parse() {
+                Ok(sound) => sound,
+                Err(_) => continue,
+            };
 
             let kind = if kind & Self::CIRCLE_FLAG > 0 {
                 $self.n_circles += 1;
@@ -337,15 +424,13 @@ macro_rules! parse_hitobjects_body {
                 let mut control_points = Vec::new();
 
                 let control_point_iter = split.next().next_field("control points")?.split('|');
-                let mut repeats: usize = split.next().next_field("repeats")?.parse()?;
 
-                if repeats > 9000 {
-                    return Err(ParseError::TooManyRepeats);
-                }
-
-                // * osu-stable treated the first span of the slider
-                // * as a repeat, but no repeats are happening
-                repeats = repeats.saturating_sub(1);
+                let repeats = match split.next().next_field("repeats")?.parse::<usize>() {
+                    // * osu-stable treated the first span of the slider
+                    // * as a repeat, but no repeats are happening
+                    Ok(repeats @ 0..=9000) => repeats.saturating_sub(1),
+                    Ok(_) | Err(_) => continue,
+                };
 
                 let mut start_idx = 0;
                 let mut end_idx = 0;
@@ -402,25 +487,25 @@ macro_rules! parse_hitobjects_body {
                 if control_points.is_empty() {
                     HitObjectKind::Circle
                 } else {
-                    let pixel_len = split
-                        .next()
-                        .next_field("pixel len")?
-                        .parse::<f64>()?
-                        .max(0.0)
-                        .min(MAX_COORDINATE_VALUE);
+                    let pixel_len = match split.next().map(str::parse::<f64>) {
+                        Some(Ok(len)) if len.is_in_custom_range(MAX_COORDINATE_VALUE as f64) => {
+                            (len != 0.0).then_some(len)
+                        }
+                        Some(_) => continue,
+                        None => None,
+                    };
 
                     let edge_sounds_opt = split.next().map(|sounds| {
                         sounds
                             .split('|')
                             .take(repeats + 2)
                             .map(parse_custom_sound)
-                            .collect::<Result<Vec<_>, _>>()
+                            .collect()
                     });
 
                     let edge_sounds = match edge_sounds_opt {
                         None => Vec::new(),
-                        Some(Ok(sounds)) => sounds,
-                        Some(Err(err)) => return Err(err),
+                        Some(sounds) => sounds,
                     };
 
                     HitObjectKind::Slider {
@@ -432,18 +517,27 @@ macro_rules! parse_hitobjects_body {
                 }
             } else if kind & Self::SPINNER_FLAG > 0 {
                 $self.n_spinners += 1;
-                let end_time = split.next().next_field("spinner endtime")?.parse()?;
+
+                let end_time = match split.next().next_field("spinner endtime")?.parse::<f64>() {
+                    Ok(end_time) => end_time.max(0.0),
+                    Err(_) => continue,
+                };
 
                 HitObjectKind::Spinner { end_time }
             } else if kind & Self::HOLD_FLAG > 0 {
                 $self.n_sliders += 1;
-                let mut end = time;
 
-                if let Some(next) = split.next() {
-                    end = end.max(next.split(':').next().next_field("hold endtime")?.parse()?);
-                }
+                let end_time = match split
+                    .next()
+                    .and_then(|next| next.split(':').next())
+                    .map(str::parse::<f64>)
+                {
+                    Some(Ok(time_)) if time_.is_in_range() => time_.max(time),
+                    Some(_) => continue,
+                    None => time,
+                };
 
-                HitObjectKind::Hold { end_time: end }
+                HitObjectKind::Hold { end_time }
             } else {
                 return Err(ParseError::UnknownHitObjectKind);
             };
@@ -453,6 +547,7 @@ macro_rules! parse_hitobjects_body {
                 start_time: time,
                 kind,
             });
+
             $self.sounds.push(sound);
 
             prev_time = time;
@@ -476,12 +571,21 @@ macro_rules! parse_hitobjects_body {
     }};
 }
 
-// Required for maps with slider edge sound values above 255 e.g. map id 80799
-fn parse_custom_sound(sound: &str) -> ParseResult<u8> {
-    sound.bytes().try_fold(0_u8, |sound, byte| match byte {
-        b'0'..=b'9' => Ok(sound.wrapping_mul(10).wrapping_add((byte & 0xF) as u8)),
-        _ => Err(ParseError::InvalidInteger),
-    })
+// Required for maps with slider edge sound values above 255 e.g. map /b/80799
+fn parse_custom_sound(sound: &str) -> u8 {
+    fn fold_str(sound: &str) -> ControlFlow<u8, u8> {
+        sound.bytes().try_fold(0_u8, |sound, byte| match byte {
+            b'0'..=b'9' => {
+                ControlFlow::Continue(sound.wrapping_mul(10).wrapping_add((byte & 0xF) as u8))
+            }
+            _ => ControlFlow::Break(0),
+        })
+    }
+
+    match fold_str(sound) {
+        ControlFlow::Continue(n) => n,
+        ControlFlow::Break(n) => n,
+    }
 }
 
 macro_rules! parse_body {
@@ -539,8 +643,6 @@ mod slider_parsing {
 
     use super::Pos2;
 
-    pub(super) const MAX_COORDINATE_VALUE: f64 = 131_072.0;
-
     pub(super) fn convert_points(
         points: &[&str],
         end_point: Option<&str>,

src/parse/pos2.rs

@@ -32,13 +32,13 @@ impl Pos2 {
     /// Return the position's length.
     #[inline]
     pub fn length(&self) -> f32 {
-        self.x.hypot(self.y)
+        ((self.x * self.x + self.y * self.y) as f64).sqrt() as f32
     }
 
     /// Return the dot product.
     #[inline]
     pub fn dot(&self, other: Self) -> f32 {
-        self.x.mul_add(other.x, self.y * other.y)
+        (self.x * other.x) + (self.y * other.y)
     }
 
     /// Return the distance to another position.
@@ -49,8 +49,12 @@ impl Pos2 {
 
     /// Normalize the coordinates with respect to the vector's length.
     #[inline]
-    pub fn normalize(self) -> Pos2 {
-        self / self.length()
+    pub fn normalize(mut self) -> Pos2 {
+        let scale = self.length().recip();
+        self.x *= scale;
+        self.y *= scale;
+
+        self
     }
 }
 

src/parse/reader.rs

@@ -138,7 +138,7 @@ impl<R> FileReader<R> {
             .and_then(|idx| {
                 self.buf[idx..]
                     .starts_with(b"osu file format v")
-                    .then(|| idx + 17)
+                    .then_some(idx + 17)
             })
             .map(|idx| {
                 let mut n = 0;
@@ -235,7 +235,7 @@ impl<R> FileReader<R> {
             .iter()
             .enumerate()
             .rev()
-            .find_map(|(i, byte)| (!matches!(byte, b' ' | b'\t')).then(|| i + 1))
+            .find_map(|(i, byte)| (!matches!(byte, b' ' | b'\t')).then_some(i + 1))
             .unwrap_or(0);
 
         self.buf.truncate(len);

src/taiko/mod.rs

@@ -5,23 +5,20 @@ mod gradual_performance;
 mod pp;
 mod rim;
 mod skills;
-mod stamina_cheese;
 mod taiko_object;
 
-pub use gradual_difficulty::*;
-pub use gradual_performance::*;
-pub use pp::*;
-use rim::Rim;
-use taiko_object::IntoTaikoObjectIter;
-
-use crate::beatmap::BeatmapHitWindows;
-use crate::{Beatmap, GameMode, Mods, OsuStars};
-
 use std::{borrow::Cow, cell::RefCell, rc::Rc};
 
-use self::colours::ColourDifficultyPreprocessor;
-use self::difficulty_object::{MonoIndex, ObjectLists, TaikoDifficultyObject};
-use self::skills::{Peaks, PeaksDifficultyValues, PeaksRaw, Skill};
+pub use self::{gradual_difficulty::*, gradual_performance::*, pp::*};
+
+use crate::{beatmap::BeatmapHitWindows, Beatmap, GameMode, Mods, OsuStars};
+
+use self::{
+    colours::ColourDifficultyPreprocessor,
+    difficulty_object::{MonoIndex, ObjectLists, TaikoDifficultyObject},
+    skills::{Peaks, PeaksDifficultyValues, PeaksRaw, Skill},
+    taiko_object::IntoTaikoObjectIter,
+};
 
 const SECTION_LEN: usize = 400;
 

src/taiko/stamina_cheese.rs

@@ -1,110 +0,0 @@
-use super::Rim;
-use crate::{limited_queue::LimitedQueue, Beatmap};
-
-const ROLL_MIN_REPETITIONS: usize = 12;
-const TL_MIN_REPETITIONS: isize = 16;
-
-pub(crate) trait StaminaCheeseDetector {
-    fn find_cheese(&self) -> Vec<bool>;
-    fn find_rolls<const PATTERN_LEN: usize, const DOUBLE_PATTERN_LEN: usize>(
-        &self,
-        cheese: &mut [bool],
-    );
-    fn find_tl_tap<const PARITY: usize, const IS_RIN: bool>(&self, cheese: &mut [bool]);
-}
-
-impl StaminaCheeseDetector for Beatmap {
-    fn find_cheese(&self) -> Vec<bool> {
-        let mut cheese = vec![false; self.hit_objects.len()];
-
-        self.find_rolls::<3, 6>(&mut cheese);
-        self.find_rolls::<4, 8>(&mut cheese);
-
-        self.find_tl_tap::<0, true>(&mut cheese);
-        self.find_tl_tap::<1, true>(&mut cheese);
-        self.find_tl_tap::<0, false>(&mut cheese);
-        self.find_tl_tap::<1, false>(&mut cheese);
-
-        cheese
-    }
-
-    fn find_rolls<const PATTERN_LEN: usize, const DOUBLE_PATTERN_LEN: usize>(
-        &self,
-        cheese: &mut [bool],
-    ) {
-        let mut history: LimitedQueue<u8, DOUBLE_PATTERN_LEN> = LimitedQueue::new();
-
-        let mut index_before_last_repeat = -1;
-        let mut last_mark_end = 0;
-
-        for (i, &h) in self.sounds.iter().enumerate() {
-            history.push(h);
-
-            if !history.full() {
-                continue;
-            }
-
-            let contains = contains_pattern_repeat::<PATTERN_LEN, DOUBLE_PATTERN_LEN>(&history);
-
-            if !contains {
-                index_before_last_repeat = (i + 1 - history.len()) as isize;
-
-                continue;
-            }
-
-            let repeated_len = (i as isize - index_before_last_repeat) as usize;
-
-            if repeated_len < ROLL_MIN_REPETITIONS {
-                continue;
-            }
-
-            mark_as_cheese(last_mark_end.max(i + 1 - repeated_len), i, cheese);
-
-            last_mark_end = i;
-        }
-    }
-
-    fn find_tl_tap<const PARITY: usize, const IS_RIN: bool>(&self, cheese: &mut [bool]) {
-        let mut tl_len = -2;
-        let mut last_mark_end = 0;
-
-        for (i, &sound) in self.sounds.iter().enumerate().skip(PARITY).step_by(2) {
-            if sound.is_rim() == IS_RIN {
-                tl_len += 2;
-            } else {
-                tl_len = -2;
-            }
-
-            if tl_len < TL_MIN_REPETITIONS {
-                continue;
-            }
-
-            let start = (i as isize + 1 - tl_len).max(last_mark_end as isize);
-            mark_as_cheese(start as usize, i, cheese);
-
-            last_mark_end = i;
-        }
-    }
-}
-
-#[inline]
-fn mark_as_cheese(start: usize, end: usize, cheese: &mut [bool]) {
-    cheese
-        .iter_mut()
-        .take(end + 1)
-        .skip(start)
-        .for_each(|b| *b = true);
-}
-
-#[inline]
-fn contains_pattern_repeat<const PATTERN_LEN: usize, const DOUBLE_PATTERN_LEN: usize>(
-    history: &LimitedQueue<u8, DOUBLE_PATTERN_LEN>,
-) -> bool {
-    for (&curr, &to_compare) in history.iter().zip(history.iter().skip(PATTERN_LEN)) {
-        if curr.is_rim() != to_compare.is_rim() {
-            return false;
-        }
-    }
-
-    true
-}