added FruitsGradualDifficultyAttributes + bunch of fruits restructuring

CHANGELOG.md

@@ -9,15 +9,13 @@
 - Added method `Beatmap::bpm`
 - Added method `max_combo` for `DifficultyAttributes`, `PerformanceAttributes`, and all `{Mode}PerformanceAttributes`
 - [BREAKING] Renamed the `attributes` field to `difficulty` for all `{Mode}PerformanceAttributes` structs
-- Added `OsuGradualDifficultyAttributes`. Suitable to calculate a map's difficulty after every or every few objects instead of calling the `stars` function over and over.
 - Added `OsuGradualPerformanceAttributes`. Suitable to calculate the performance on a map after every or every few objects instead of using `OsuPP` over and over.
 - Fixed incorrect attributes on maps with only 1 or 2 hit objects for all modes
 - [BREAKING] Replaced field `FruitsDifficultyAttributes::max_combo` by a method with the same name
 - Added methods `TaikoDifficultyAttributes::max_combo` and `OsuDifficultyAttributes::max_combo`
-- Added `ManiaGradualDifficultyAttributes`. Suitable to calculate a map's difficulty after every or every few objects instead of calling the `stars` function over and over.
 - Added `ManiaGradualPerformanceAttributes`. Suitable to calculate the performance on a map after every or every few objects instead of using `ManiaPP` over and over.
-- Added `TaikoGradualDifficultyAttributes`. Suitable to calculate a map's difficulty after every or every few objects instead of calling the `stars` function over and over.
 - Added `TaikoGradualPerformanceAttributes`. Suitable to calculate the performance on a map after every or every few objects instead of using `TaikoPP` over and over.
+- Added structs `{Mode}GradualDifficultyAttributes`. Suitable to calculate a map's difficulty after every or every few objects instead of calling the mode's `stars` function over and over.
 
 # v0.3.0
 

src/control_point_iter.rs

@@ -13,6 +13,7 @@ macro_rules! next_tuple {
     };
 }
 
+#[derive(Clone, Debug)]
 pub(crate) struct ControlPointIter<'p> {
     timing_points: Iter<'p, TimingPoint>,
     difficulty_points: Iter<'p, DifficultyPoint>,
@@ -37,7 +38,7 @@ impl<'p> ControlPointIter<'p> {
     }
 }
 
-#[derive(Debug)]
+#[derive(Copy, Clone, Debug)]
 pub(crate) enum ControlPoint {
     Timing { time: f64, beat_len: f64 },
     Difficulty { time: f64, slider_velocity: f64 },

src/curve.rs

@@ -8,13 +8,13 @@ const BEZIER_TOLERANCE: f32 = 0.25;
 const CATMULL_DETAIL: usize = 50;
 const CIRCULAR_ARC_TOLERANCE: f32 = 0.1;
 
-#[derive(Default)]
+#[derive(Clone, Debug, Default)]
 pub(crate) struct CurveBuffers {
     vertices: Vec<Pos2>,
     bezier: BezierBuffers,
 }
 
-#[derive(Default)]
+#[derive(Clone, Debug, Default)]
 struct BezierBuffers {
     buf1: Vec<Pos2>,
     buf2: Vec<Pos2>,

src/fruits/catch_object.rs

@@ -1,9 +1,11 @@
 use crate::parse::Pos2;
 
+use super::fruit_or_juice::FruitParams;
+
 const PLAYFIELD_WIDTH: f32 = 512.0;
 const BASE_SPEED: f64 = 1.0;
 
-#[derive(Clone)]
+#[derive(Clone, Debug)]
 pub struct CatchObject {
     pub(crate) pos: f32,
     pub(crate) time: f64,
@@ -23,11 +25,11 @@ impl CatchObject {
         }
     }
 
-    pub(crate) fn with_hr(mut self, last_pos: &mut Option<f32>, last_time: &mut f64) -> Self {
+    pub(crate) fn with_hr(mut self, params: &mut FruitParams<'_>) -> Self {
         let mut offset_pos = self.pos;
-        let time_diff = self.time - *last_time;
+        let time_diff = self.time - params.last_time;
 
-        if let Some(last_pos_ref) = last_pos.filter(|_| time_diff <= 1000.0) {
+        if let Some(last_pos_ref) = params.last_pos.filter(|_| time_diff <= 1000.0) {
             let pos_diff = offset_pos - last_pos_ref;
 
             if pos_diff.abs() > f32::EPSILON {
@@ -41,14 +43,14 @@ impl CatchObject {
                     }
                 }
 
-                last_pos.replace(offset_pos);
-                *last_time = self.time;
+                params.last_pos.replace(offset_pos);
+                params.last_time = self.time;
             }
 
             self.pos = offset_pos;
         } else {
-            last_pos.replace(offset_pos);
-            *last_time = self.time;
+            params.last_pos.replace(offset_pos);
+            params.last_time = self.time;
         }
 
         self

src/fruits/fruit_or_juice.rs

@@ -0,0 +1,272 @@
+use std::{iter::Map, vec::IntoIter};
+
+use crate::{
+    curve::{Curve, CurveBuffers},
+    parse::{HitObject, HitObjectKind, Pos2},
+    Beatmap,
+};
+
+use super::{catch_object::CatchObject, slider_state::SliderState, FruitsDifficultyAttributes};
+
+const LEGACY_LAST_TICK_OFFSET: f64 = 36.0;
+const BASE_SCORING_DISTANCE: f64 = 100.0;
+
+#[derive(Clone, Debug)]
+pub(crate) struct FruitParams<'a> {
+    pub(crate) attributes: FruitsDifficultyAttributes,
+    pub(crate) curve_bufs: CurveBuffers,
+    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,
+}
+
+type JuiceStream = Map<IntoIter<(Pos2, f64)>, fn((Pos2, f64)) -> CatchObject>;
+
+#[derive(Clone, Debug)]
+pub(crate) enum FruitOrJuice {
+    Fruit(Option<CatchObject>),
+    Juice(JuiceStream),
+}
+
+impl FruitOrJuice {
+    pub(crate) fn new(h: &HitObject, params: &mut FruitParams<'_>) -> Option<Self> {
+        match &h.kind {
+            HitObjectKind::Circle => {
+                let mut h = CatchObject::new((h.pos, h.start_time));
+
+                if params.with_hr {
+                    h = h.with_hr(params);
+                }
+
+                params.attributes.n_fruits += 1;
+
+                Some(FruitOrJuice::Fruit(Some(h)))
+            }
+            HitObjectKind::Slider {
+                pixel_len,
+                repeats,
+                control_points,
+            } => {
+                // HR business
+                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 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;
+
+                // * 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
+                // * been edited by the user, and should never be reached in normal usage.
+                let max_len = 100_000.0;
+
+                let len = curve.dist().min(max_len);
+                tick_dist = tick_dist.clamp(0.0, len);
+                let min_dist_from_end = velocity * 10.0;
+
+                let mut curr_dist = tick_dist;
+                let time_add = duration * tick_dist / (*pixel_len * span_count);
+
+                let target = *pixel_len - tick_dist / 8.0;
+
+                params.ticks.reserve((target / tick_dist) as usize);
+
+                // Tick of the first span
+                while curr_dist < len - min_dist_from_end {
+                    let progress = curr_dist / len;
+                    let pos = h.pos + curve.position_at(progress);
+                    let time = h.start_time + progress * span_duration;
+                    params.ticks.push((pos, time));
+                    curr_dist += tick_dist;
+                }
+
+                params.attributes.n_tiny_droplets += tiny_droplet_count(
+                    h.start_time,
+                    time_add,
+                    duration,
+                    span_count as usize,
+                    &params.ticks,
+                );
+
+                let mut slider_objects =
+                    Vec::with_capacity(span_count as usize * (params.ticks.len() + 1));
+                slider_objects.push((h.pos, h.start_time));
+
+                // Other spans
+                if *repeats == 0 {
+                    slider_objects.append(&mut params.ticks); // automatically empties buffer for next slider
+                } else {
+                    slider_objects.extend(&params.ticks);
+
+                    for span_idx in 1..=*repeats {
+                        let progress = (span_idx % 2 == 1) as u8 as f64;
+                        let pos = h.pos + curve.position_at(progress);
+                        let time_offset = span_duration * span_idx as f64;
+
+                        // Reverse tick
+                        slider_objects.push((pos, h.start_time + time_offset));
+
+                        let new_ticks = params.ticks.iter().enumerate().map(|(i, (pos, time))| {
+                            (*pos, *time + time_offset + time_add * i as f64)
+                        });
+
+                        // Actual ticks
+                        if span_idx & 1 == 1 {
+                            slider_objects.extend(new_ticks.rev());
+                        } else {
+                            slider_objects.extend(new_ticks);
+                        }
+                    }
+
+                    params.ticks.clear();
+                }
+
+                // 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));
+
+                let new_fruits = *repeats + 2;
+                params.attributes.n_fruits += new_fruits;
+                params.attributes.n_droplets += slider_objects.len() - new_fruits;
+
+                let iter = slider_objects
+                    .into_iter()
+                    .map(CatchObject::new as fn(_) -> _);
+
+                Some(FruitOrJuice::Juice(iter))
+            }
+            HitObjectKind::Spinner { .. } | HitObjectKind::Hold { .. } => None,
+        }
+    }
+}
+
+impl Iterator for FruitOrJuice {
+    type Item = CatchObject;
+
+    #[inline]
+    fn next(&mut self) -> Option<Self::Item> {
+        match self {
+            Self::Fruit(fruit) => fruit.take(),
+            Self::Juice(slider) => slider.next(),
+        }
+    }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        let len = self.len();
+
+        (len, Some(len))
+    }
+}
+
+impl ExactSizeIterator for FruitOrJuice {
+    #[inline]
+    fn len(&self) -> usize {
+        match self {
+            FruitOrJuice::Fruit(Some(_)) => 1,
+            FruitOrJuice::Fruit(None) => 0,
+            FruitOrJuice::Juice(slider) => slider.len(),
+        }
+    }
+}
+
+// BUG: Sometimes there are off-by-one errors,
+// presumably caused by floating point inaccuracies
+fn tiny_droplet_count(
+    start_time: f64,
+    time_between_ticks: f64,
+    duration: f64,
+    span_count: usize,
+    ticks: &[(Pos2, f64)],
+) -> usize {
+    // tiny droplets preceeding a _tick_
+    let per_tick = if !ticks.is_empty() && time_between_ticks > 80.0 {
+        let time_between_tiny = shrink_down(time_between_ticks);
+
+        // add a little for floating point inaccuracies
+        let start = time_between_tiny + 0.001;
+
+        count_iterations(start, time_between_tiny, time_between_ticks)
+    } else {
+        0
+    };
+
+    // tiny droplets preceeding a _reverse_
+    let last = ticks.last().map_or(start_time, |(_, last)| *last);
+    let repeat_time = start_time + duration / span_count as f64;
+    let since_last_tick = repeat_time - last;
+
+    let span_last_section = if since_last_tick > 80.0 {
+        let time_between_tiny = shrink_down(since_last_tick);
+
+        count_iterations(time_between_tiny, time_between_tiny, since_last_tick)
+    } else {
+        0
+    };
+
+    // tiny droplets preceeding the slider tail
+    // necessary to handle distinctly because of the legacy last tick
+    let last = ticks.last().map_or(start_time, |(_, last)| *last);
+    let end_time = start_time + duration / span_count as f64 - LEGACY_LAST_TICK_OFFSET;
+    let since_last_tick = end_time - last;
+
+    let last_section = if since_last_tick > 80.0 {
+        let time_between_tiny = shrink_down(since_last_tick);
+
+        count_iterations(time_between_tiny, time_between_tiny, since_last_tick)
+    } else {
+        0
+    };
+
+    // Combine tiny droplets counts
+    per_tick * ticks.len() * span_count
+        + span_last_section * (span_count.saturating_sub(1))
+        + last_section
+}
+
+#[inline]
+fn shrink_down(mut val: f64) -> f64 {
+    while val > 100.0 {
+        val /= 2.0;
+    }
+
+    val
+}
+
+#[inline]
+fn count_iterations(mut start: f64, step: f64, end: f64) -> usize {
+    let mut count = 0;
+
+    while start < end {
+        count += 1;
+        start += step;
+    }
+
+    count
+}

src/fruits/gradual_difficulty.rs

@@ -0,0 +1,239 @@
+use std::{iter, slice::Iter};
+
+use crate::{
+    curve::CurveBuffers,
+    fruits::{
+        difficulty_object::DifficultyObject, slider_state::SliderState, SECTION_LENGTH,
+        STAR_SCALING_FACTOR,
+    },
+    parse::{HitObject, Pos2},
+    Beatmap, Mods,
+};
+
+use super::{
+    calculate_catch_width,
+    catch_object::CatchObject,
+    fruit_or_juice::{FruitOrJuice, FruitParams},
+    movement::Movement,
+    FruitsDifficultyAttributes, ALLOWED_CATCH_RANGE,
+};
+
+/// Gradually calculate the difficulty attributes of an osu!ctb map.
+///
+/// Note that this struct implements [`Iterator`](std::iter::Iterator).
+/// On every call of [`Iterator::next`](std::iter::Iterator::next), the map's next hit object will
+/// be processed and the [`FruitsDifficultyAttributes`] will be updated and returned.
+///
+/// If you want to calculate performance attributes, use
+/// [`FruitsGradualPerformanceAttributes`](crate::fruits::FruitsGradualPerformanceAttributes) instead.
+///
+/// # Example
+///
+/// ```
+/// use rosu_pp::{Beatmap, fruits::FruitsGradualDifficultyAttributes};
+///
+/// # /*
+/// let map: Beatmap = ...
+/// # */
+/// # let map = Beatmap::default();
+///
+/// let mods = 64; // DT
+/// let mut iter = FruitsGradualDifficultyAttributes::new(&map, mods);
+///
+/// let attrs1 = iter.next(); // the difficulty of the map after the first hit object
+/// let attrs2 = iter.next(); //                           after the second hit object
+///
+/// // Remaining hit objects
+/// for difficulty in iter {
+///     // ...
+/// }
+/// ```
+#[derive(Clone, Debug)]
+pub struct FruitsGradualDifficultyAttributes<'map> {
+    pub(crate) idx: usize,
+    clock_rate: f64,
+    hit_objects: FruitsObjectIter<'map>,
+    movement: Movement,
+    prev: CatchObject,
+    half_catcher_width: f64,
+    last_direction: i8,
+    last_excess: f64,
+    curr_section_end: f64,
+    strain_peak_buf: Vec<f64>,
+}
+
+impl<'map> FruitsGradualDifficultyAttributes<'map> {
+    /// Create a new difficulty attributes iterator for osu!ctb maps.
+    pub fn new(map: &'map Beatmap, mods: impl Mods) -> Self {
+        let map_attributes = map.attributes().mods(mods);
+
+        let attributes = FruitsDifficultyAttributes {
+            ar: map_attributes.ar,
+            ..Default::default()
+        };
+
+        let hit_objects = FruitsObjectIter::new(map, mods, attributes);
+
+        let half_catcher_width =
+            (calculate_catch_width(map_attributes.cs as f32) / 2.0 / ALLOWED_CATCH_RANGE) as f64;
+        let last_direction = 0;
+        let last_excess = half_catcher_width;
+
+        let movement = Movement::new(map_attributes.cs as f32);
+        let prev = CatchObject::new((Pos2::zero(), 0.0));
+
+        Self {
+            idx: 0,
+            clock_rate: mods.speed(),
+            hit_objects,
+            movement,
+            prev,
+            half_catcher_width,
+            last_direction,
+            last_excess,
+            curr_section_end: 0.0,
+            strain_peak_buf: Vec::new(),
+        }
+    }
+
+    fn init_hyper_dash(&mut self, next: &CatchObject) {
+        self.prev.init_hyper_dash(
+            self.half_catcher_width,
+            next,
+            &mut self.last_direction,
+            &mut self.last_excess,
+        );
+    }
+}
+
+impl Iterator for FruitsGradualDifficultyAttributes<'_> {
+    type Item = FruitsDifficultyAttributes;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let curr = self.hit_objects.next()?;
+        self.idx += 1;
+
+        if self.idx == 1 {
+            self.prev = curr;
+
+            return Some(self.hit_objects.attributes());
+        }
+
+        self.init_hyper_dash(&curr);
+
+        let h = DifficultyObject::new(
+            &curr,
+            &self.prev,
+            self.movement.half_catcher_width,
+            self.clock_rate,
+        );
+
+        if self.idx == 2 {
+            self.curr_section_end =
+                (h.base.time / self.clock_rate / SECTION_LENGTH).ceil() * SECTION_LENGTH;
+        } else {
+            let base_time = h.base.time / self.clock_rate;
+
+            while base_time > self.curr_section_end {
+                self.movement.save_current_peak();
+                self.movement.start_new_section_from(self.curr_section_end);
+                self.curr_section_end += SECTION_LENGTH;
+            }
+        }
+
+        self.movement.process(&h);
+        self.prev = curr;
+
+        let len = self.movement.strain_peaks.len();
+        let missing = len + 1 - self.strain_peak_buf.len();
+        self.strain_peak_buf.extend(iter::repeat(0.0).take(missing));
+
+        self.strain_peak_buf[..len].copy_from_slice(&self.movement.strain_peaks);
+
+        if let Some(last) = self.strain_peak_buf.last_mut() {
+            *last = self.movement.curr_section_peak;
+        }
+
+        let mut attributes = self.hit_objects.attributes();
+        attributes.stars =
+            Movement::difficulty_value(&mut self.strain_peak_buf).sqrt() * STAR_SCALING_FACTOR;
+
+        Some(attributes)
+    }
+}
+
+#[derive(Clone, Debug)]
+struct FruitsObjectIter<'map> {
+    last_object: Option<FruitOrJuice>,
+    hit_objects: Iter<'map, HitObject>,
+    params: FruitParams<'map>,
+}
+
+impl<'map> FruitsObjectIter<'map> {
+    fn new(map: &'map Beatmap, mods: impl Mods, attributes: FruitsDifficultyAttributes) -> Self {
+        let params = FruitParams {
+            attributes,
+            curve_bufs: CurveBuffers::default(),
+            last_pos: None,
+            last_time: 0.0,
+            map,
+            slider_state: SliderState::new(map),
+            ticks: Vec::new(),
+            with_hr: mods.hr(),
+        };
+
+        Self {
+            last_object: None,
+            hit_objects: map.hit_objects.iter(),
+            params,
+        }
+    }
+
+    fn attributes(&self) -> FruitsDifficultyAttributes {
+        self.params.attributes.clone()
+    }
+}
+
+impl Iterator for FruitsObjectIter<'_> {
+    type Item = CatchObject;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if let Some(h) = self.last_object.as_mut().and_then(Iterator::next) {
+            return Some(h);
+        }
+
+        while let Some(h) = self.hit_objects.next() {
+            if let Some(h) = FruitOrJuice::new(h, &mut self.params) {
+                return self.last_object.insert(h).next();
+            }
+        }
+
+        None
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn empty_map() {
+        let map = Beatmap::default();
+        let mut attributes = FruitsGradualDifficultyAttributes::new(&map, 0);
+        assert!(attributes.next().is_none());
+    }
+
+    #[cfg(not(any(feature = "async_tokio", feature = "async_std")))]
+    #[test]
+    fn iter_end_eq_regular() {
+        let map = Beatmap::from_path("./maps/2118524.osu").expect("failed to parse map");
+        let mods = 64;
+        let regular = crate::fruits::stars(&map, mods, None);
+
+        let iter_end = FruitsGradualDifficultyAttributes::new(&map, mods)
+            .last()
+            .expect("empty iter");
+
+        assert_eq!(regular, iter_end);
+    }
+}

src/fruits/mod.rs

@@ -2,21 +2,21 @@
 
 mod catch_object;
 mod difficulty_object;
+mod fruit_or_juice;
+mod gradual_difficulty;
 mod movement;
 mod pp;
 mod slider_state;
 
 use catch_object::CatchObject;
 use difficulty_object::DifficultyObject;
+use fruit_or_juice::FruitOrJuice;
+pub use gradual_difficulty::*;
 use movement::Movement;
 pub use pp::*;
 use slider_state::SliderState;
 
-use crate::{
-    curve::{Curve, CurveBuffers},
-    parse::{HitObjectKind, Pos2},
-    Beatmap, Mods, Strains,
-};
+use crate::{curve::CurveBuffers, fruits::fruit_or_juice::FruitParams, Beatmap, Mods, Strains};
 
 const SECTION_LENGTH: f64 = 750.0;
 const STAR_SCALING_FACTOR: f64 = 0.153;
@@ -24,9 +24,6 @@ const STAR_SCALING_FACTOR: f64 = 0.153;
 const ALLOWED_CATCH_RANGE: f32 = 0.8;
 const CATCHER_SIZE: f32 = 106.75;
 
-const LEGACY_LAST_TICK_OFFSET: f64 = 36.0;
-const BASE_SCORING_DISTANCE: f64 = 100.0;
-
 /// Difficulty calculation for osu!ctb maps.
 ///
 /// In case of a partial play, e.g. a fail, one can specify the amount of passed objects.
@@ -36,7 +33,8 @@ pub fn stars(
     passed_objects: Option<usize>,
 ) -> FruitsDifficultyAttributes {
     let (mut movement, mut attributes) = calculate_movement(map, mods, passed_objects);
-    attributes.stars = movement.difficulty_value().sqrt() * STAR_SCALING_FACTOR;
+    attributes.stars =
+        Movement::difficulty_value(&mut movement.strain_peaks).sqrt() * STAR_SCALING_FACTOR;
 
     attributes
 }
@@ -62,146 +60,28 @@ fn calculate_movement(
     let take = passed_objects.unwrap_or(usize::MAX);
 
     let map_attributes = map.attributes().mods(mods);
-    let with_hr = mods.hr();
-    let mut ticks = Vec::new(); // using the same buffer for all sliders
-    let mut slider_state = SliderState::new(map);
-    let mut curve_bufs = CurveBuffers::default();
 
-    let mut attributes = FruitsDifficultyAttributes {
+    let attributes = FruitsDifficultyAttributes {
         ar: map_attributes.ar,
         ..Default::default()
     };
 
+    let mut params = FruitParams {
+        attributes,
+        curve_bufs: CurveBuffers::default(),
+        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(),
+    };
+
     // BUG: Incorrect object order on 2B maps that have fruits within sliders
     let mut hit_objects = map
         .hit_objects
         .iter()
-        .scan((None, 0.0), |(last_pos, last_time), h| match &h.kind {
-            HitObjectKind::Circle => {
-                let mut h = CatchObject::new((h.pos, h.start_time));
-
-                if with_hr {
-                    h = h.with_hr(last_pos, last_time);
-                }
-
-                attributes.n_fruits += 1;
-
-                Some(Some(FruitOrJuice::Fruit(Some(h))))
-            }
-            HitObjectKind::Slider {
-                pixel_len,
-                repeats,
-                control_points,
-            } => {
-                // HR business
-                *last_pos = Some(h.pos.x + control_points[control_points.len() - 1].pos.x);
-                *last_time = h.start_time;
-
-                // Responsible for timing point values
-                slider_state.update(h.start_time);
-
-                let span_count = (*repeats + 1) as f64;
-
-                let mut tick_dist = 100.0 * map.slider_mult / map.tick_rate;
-
-                if map.version >= 8 {
-                    tick_dist /=
-                        (100.0 / 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 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;
-
-                // * 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
-                // * been edited by the user, and should never be reached in normal usage.
-                let max_len = 100_000.0;
-
-                let len = curve.dist().min(max_len);
-                tick_dist = tick_dist.clamp(0.0, len);
-                let min_dist_from_end = velocity * 10.0;
-
-                let mut curr_dist = tick_dist;
-                let time_add = duration * tick_dist / (*pixel_len * span_count);
-
-                let target = *pixel_len - tick_dist / 8.0;
-
-                ticks.reserve((target / tick_dist) as usize);
-
-                // Tick of the first span
-                while curr_dist < len - min_dist_from_end {
-                    let progress = curr_dist / len;
-                    let pos = h.pos + curve.position_at(progress);
-                    let time = h.start_time + progress * span_duration;
-                    ticks.push((pos, time));
-                    curr_dist += tick_dist;
-                }
-
-                attributes.n_tiny_droplets += tiny_droplet_count(
-                    h.start_time,
-                    time_add,
-                    duration,
-                    span_count as usize,
-                    &ticks,
-                );
-
-                let mut slider_objects =
-                    Vec::with_capacity(span_count as usize * (ticks.len() + 1));
-                slider_objects.push((h.pos, h.start_time));
-
-                // Other spans
-                if *repeats == 0 {
-                    slider_objects.append(&mut ticks); // automatically empties buffer for next slider
-                } else {
-                    slider_objects.extend(&ticks);
-
-                    for span_idx in 1..=*repeats {
-                        let progress = (span_idx % 2 == 1) as u8 as f64;
-                        let pos = h.pos + curve.position_at(progress);
-                        let time_offset = span_duration * span_idx as f64;
-
-                        // Reverse tick
-                        slider_objects.push((pos, h.start_time + time_offset));
-
-                        let new_ticks = ticks.iter().enumerate().map(|(i, (pos, time))| {
-                            (*pos, *time + time_offset + time_add * i as f64)
-                        });
-
-                        // Actual ticks
-                        if span_idx & 1 == 1 {
-                            slider_objects.extend(new_ticks.rev());
-                        } else {
-                            slider_objects.extend(new_ticks);
-                        }
-                    }
-
-                    ticks.clear();
-                }
-
-                // 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));
-
-                let new_fruits = *repeats + 2;
-                attributes.n_fruits += new_fruits;
-                attributes.n_droplets += slider_objects.len() - new_fruits;
-
-                let iter = slider_objects.into_iter().map(CatchObject::new);
-
-                Some(Some(FruitOrJuice::Juice(iter)))
-            }
-            HitObjectKind::Spinner { .. } | HitObjectKind::Hold { .. } => Some(None),
-        })
-        .flatten()
+        .filter_map(|h| FruitOrJuice::new(h, &mut params))
         .flatten()
         .take(take);
 
@@ -213,16 +93,15 @@ fn calculate_movement(
 
     // Strain business
     let mut movement = Movement::new(map_attributes.cs as f32);
-    let section_len = SECTION_LENGTH * map_attributes.clock_rate;
 
-    let (mut prev, mut curr) = match (hit_objects.next(), hit_objects.next()) {
+    let (mut prev, curr) = match (hit_objects.next(), hit_objects.next()) {
         (Some(prev), Some(curr)) => (prev, curr),
-        (Some(_), None) | (None, None) => return (movement, attributes),
+        (Some(_), None) | (None, None) => return (movement, params.attributes),
         (None, Some(_)) => unreachable!(),
     };
 
-    // TODO: time of second second object instead?
-    let mut curr_section_end = (prev.time / section_len).ceil() * section_len;
+    let mut curr_section_end =
+        (curr.time / map_attributes.clock_rate / SECTION_LENGTH).ceil() * SECTION_LENGTH;
 
     prev.init_hyper_dash(
         half_catcher_width,
@@ -231,15 +110,7 @@ fn calculate_movement(
         &mut last_excess,
     );
 
-    // Handle second object separately to remove later if-branching
-    let next = hit_objects.next().unwrap();
-    curr.init_hyper_dash(
-        half_catcher_width,
-        &next,
-        &mut last_direction,
-        &mut last_excess,
-    );
-
+    // Handle first object distinctly
     let h = DifficultyObject::new(
         &curr,
         &prev,
@@ -247,20 +118,14 @@ fn calculate_movement(
         map_attributes.clock_rate,
     );
 
-    while h.base.time > curr_section_end {
-        curr_section_end += section_len;
-    }
-
     movement.process(&h);
-
     prev = curr;
-    curr = next;
 
     // Handle all other objects
-    for next in hit_objects {
-        curr.init_hyper_dash(
+    for curr in hit_objects {
+        prev.init_hyper_dash(
             half_catcher_width,
-            &next,
+            &curr,
             &mut last_direction,
             &mut last_excess,
         );
@@ -272,112 +137,21 @@ fn calculate_movement(
             map_attributes.clock_rate,
         );
 
-        while h.base.time > curr_section_end {
+        let base_time = h.base.time / map_attributes.clock_rate;
+
+        while base_time > curr_section_end {
             movement.save_current_peak();
-            movement.start_new_section_from(curr_section_end / map_attributes.clock_rate);
-            curr_section_end += section_len;
+            movement.start_new_section_from(curr_section_end);
+            curr_section_end += SECTION_LENGTH;
         }
 
         movement.process(&h);
-
         prev = curr;
-        curr = next;
     }
 
-    // Same as in loop but without init_hyper_dash because `curr` is the last element
-    let h = DifficultyObject::new(
-        &curr,
-        &prev,
-        movement.half_catcher_width,
-        map_attributes.clock_rate,
-    );
-
-    while h.base.time > curr_section_end {
-        movement.save_current_peak();
-        movement.start_new_section_from(curr_section_end / map_attributes.clock_rate);
-
-        curr_section_end += section_len;
-    }
-
-    movement.process(&h);
     movement.save_current_peak();
 
-    (movement, attributes)
-}
-
-// BUG: Sometimes there are off-by-one errors,
-// presumably caused by floating point inaccuracies
-fn tiny_droplet_count(
-    start_time: f64,
-    time_between_ticks: f64,
-    duration: f64,
-    span_count: usize,
-    ticks: &[(Pos2, f64)],
-) -> usize {
-    // tiny droplets preceeding a _tick_
-    let per_tick = if !ticks.is_empty() && time_between_ticks > 80.0 {
-        let time_between_tiny = shrink_down(time_between_ticks);
-
-        // add a little for floating point inaccuracies
-        let start = time_between_tiny + 0.001;
-
-        count_iterations(start, time_between_tiny, time_between_ticks)
-    } else {
-        0
-    };
-
-    // tiny droplets preceeding a _reverse_
-    let last = ticks.last().map_or(start_time, |(_, last)| *last);
-    let repeat_time = start_time + duration / span_count as f64;
-    let since_last_tick = repeat_time - last;
-
-    let span_last_section = if since_last_tick > 80.0 {
-        let time_between_tiny = shrink_down(since_last_tick);
-
-        count_iterations(time_between_tiny, time_between_tiny, since_last_tick)
-    } else {
-        0
-    };
-
-    // tiny droplets preceeding the slider tail
-    // necessary to handle distinctly because of the legacy last tick
-    let last = ticks.last().map_or(start_time, |(_, last)| *last);
-    let end_time = start_time + duration / span_count as f64 - LEGACY_LAST_TICK_OFFSET;
-    let since_last_tick = end_time - last;
-
-    let last_section = if since_last_tick > 80.0 {
-        let time_between_tiny = shrink_down(since_last_tick);
-
-        count_iterations(time_between_tiny, time_between_tiny, since_last_tick)
-    } else {
-        0
-    };
-
-    // Combine tiny droplets counts
-    per_tick * ticks.len() * span_count
-        + span_last_section * (span_count.saturating_sub(1))
-        + last_section
-}
-
-#[inline]
-fn shrink_down(mut val: f64) -> f64 {
-    while val > 100.0 {
-        val /= 2.0;
-    }
-
-    val
-}
-
-#[inline]
-fn count_iterations(mut start: f64, step: f64, end: f64) -> usize {
-    let mut count = 0;
-
-    while start < end {
-        count += 1;
-        start += step;
-    }
-
-    count
+    (movement, params.attributes)
 }
 
 #[inline]
@@ -387,34 +161,8 @@ pub(crate) fn calculate_catch_width(cs: f32) -> f32 {
     CATCHER_SIZE * scale.abs() * ALLOWED_CATCH_RANGE
 }
 
-enum FruitOrJuice<I> {
-    Fruit(Option<CatchObject>),
-    Juice(I),
-}
-
-impl<I: Iterator<Item = CatchObject>> Iterator for FruitOrJuice<I> {
-    type Item = CatchObject;
-
-    #[inline]
-    fn next(&mut self) -> Option<Self::Item> {
-        match self {
-            Self::Fruit(fruit) => fruit.take(),
-            Self::Juice(slider) => slider.next(),
-        }
-    }
-
-    #[inline]
-    fn size_hint(&self) -> (usize, Option<usize>) {
-        match self {
-            Self::Fruit(Some(_)) => (1, Some(1)),
-            Self::Fruit(None) => (0, Some(0)),
-            Self::Juice(slider) => slider.size_hint(),
-        }
-    }
-}
-
 /// The result of a difficulty calculation on an osu!ctb map.
-#[derive(Clone, Debug, Default)]
+#[derive(Clone, Debug, Default, PartialEq)]
 pub struct FruitsDifficultyAttributes {
     /// The final star rating
     pub stars: f64,

src/fruits/movement.rs

@@ -10,6 +10,7 @@ const SKILL_MULTIPLIER: f64 = 900.0;
 const STRAIN_DECAY_BASE: f64 = 0.2;
 const DECAY_WEIGHT: f64 = 0.94;
 
+#[derive(Clone, Debug)]
 pub(crate) struct Movement {
     pub(crate) half_catcher_width: f32,
 
@@ -18,7 +19,7 @@ pub(crate) struct Movement {
     last_strain_time: f64,
 
     current_strain: f64,
-    current_section_peak: f64,
+    pub(crate) curr_section_peak: f64,
 
     pub(crate) strain_peaks: Vec<f64>,
     prev_time: Option<f64>,
@@ -38,7 +39,7 @@ impl Movement {
             last_strain_time: 0.0,
 
             current_strain: 1.0,
-            current_section_peak: 1.0,
+            curr_section_peak: 1.0,
 
             strain_peaks: Vec::with_capacity(128),
             prev_time: None,
@@ -47,29 +48,28 @@ impl Movement {
 
     #[inline]
     pub(crate) fn save_current_peak(&mut self) {
-        self.strain_peaks.push(self.current_section_peak);
+        self.strain_peaks.push(self.curr_section_peak);
     }
 
     #[inline]
     pub(crate) fn start_new_section_from(&mut self, time: f64) {
-        self.current_section_peak = self.peak_strain(time - self.prev_time.unwrap());
+        self.curr_section_peak = self.peak_strain(time - self.prev_time.unwrap());
     }
 
     pub(crate) fn process(&mut self, current: &DifficultyObject<'_>) {
         self.current_strain *= strain_decay(current.delta);
         self.current_strain += self.strain_value_of(current) * SKILL_MULTIPLIER;
-        self.current_section_peak = self.current_strain.max(self.current_section_peak);
+        self.curr_section_peak = self.current_strain.max(self.curr_section_peak);
         self.prev_time.replace(current.start_time);
     }
 
-    pub(crate) fn difficulty_value(&mut self) -> f64 {
+    pub(crate) fn difficulty_value(strain_peaks: &mut [f64]) -> f64 {
         let mut difficulty = 0.0;
         let mut weight = 1.0;
 
-        self.strain_peaks
-            .sort_unstable_by(|a, b| b.partial_cmp(a).unwrap_or(Ordering::Equal));
+        strain_peaks.sort_unstable_by(|a, b| b.partial_cmp(a).unwrap_or(Ordering::Equal));
 
-        for &strain in self.strain_peaks.iter() {
+        for &strain in strain_peaks.iter() {
             difficulty += strain * weight;
             weight *= DECAY_WEIGHT;
         }

src/fruits/slider_state.rs

@@ -1,5 +1,6 @@
 use crate::{Beatmap, ControlPoint, ControlPointIter};
 
+#[derive(Clone, Debug)]
 pub(crate) struct SliderState<'p> {
     control_points: ControlPointIter<'p>,
     next: Option<ControlPoint>,