refactor: split cargo workspace

crates/algorithms/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "jay-algorithms"
+version = "0.4.0"
+edition = "2024"
+license = "GPL-3.0-only"
+description = "Internal dependency of the Jay compositor"
+repository = "https://github.com/mahkoh/jay"
+
+[dependencies]
+smallvec = { version = "1.8.0", features = ["const_generics", "const_new", "union"] }

crates/algorithms/src/lib.rs

@@ -0,0 +1,10 @@
+#![allow(
+    clippy::mem_replace_with_default,
+    clippy::comparison_chain,
+    clippy::collapsible_else_if,
+    clippy::needless_lifetimes
+)]
+
+pub mod qoi;
+pub mod rect;
+mod windows;

crates/algorithms/src/qoi.rs

@@ -0,0 +1,91 @@
+pub fn xrgb8888_encode_qoi(bytes: &[u8], width: u32, height: u32, stride: u32) -> Vec<u8> {
+    const OP_RGB: u8 = 0b1111_1110;
+    const OP_INDEX: u8 = 0b0000_0000;
+    const OP_DIFF: u8 = 0b0100_0000;
+    const OP_LUMA: u8 = 0b1000_0000;
+    const OP_RUN: u8 = 0b1100_0000;
+
+    let mut res = vec![];
+    let width_bytes_be = width.to_be_bytes();
+    let height_bytes_be = height.to_be_bytes();
+    let header = [
+        b'q',
+        b'o',
+        b'i',
+        b'f',
+        width_bytes_be[0],
+        width_bytes_be[1],
+        width_bytes_be[2],
+        width_bytes_be[3],
+        height_bytes_be[0],
+        height_bytes_be[1],
+        height_bytes_be[2],
+        height_bytes_be[3],
+        3,
+        0,
+    ];
+    res.extend_from_slice(&header);
+    let mut prev_pixel = [0, 0, 0, 0xff];
+    let mut array = [[0; 4]; 64];
+    let mut run_length = 0;
+    for line in bytes.chunks_exact(stride as _) {
+        for &pixel in array_chunks::<_, 4>(&line[..(width * 4) as _]) {
+            let pixel = [pixel[2], pixel[1], pixel[0], 0xff];
+            if pixel == prev_pixel {
+                run_length += 1;
+                if run_length == 62 {
+                    res.push(OP_RUN | (run_length - 1));
+                    run_length = 0;
+                }
+                continue;
+            }
+            if run_length > 0 {
+                res.push(OP_RUN | (run_length - 1));
+                run_length = 0;
+            }
+            let prev = prev_pixel;
+            prev_pixel = pixel;
+            let index = {
+                let sum = 0u8
+                    .wrapping_add(pixel[0].wrapping_mul(3))
+                    .wrapping_add(pixel[1].wrapping_mul(5))
+                    .wrapping_add(pixel[2].wrapping_mul(7))
+                    .wrapping_add(255u8.wrapping_mul(11));
+                sum & 63
+            };
+            if array[index as usize] == pixel {
+                res.push(OP_INDEX | index);
+                continue;
+            }
+            array[index as usize] = pixel;
+            let dr = pixel[0].wrapping_sub(prev[0]);
+            let dg = pixel[1].wrapping_sub(prev[1]);
+            let db = pixel[2].wrapping_sub(prev[2]);
+            let dr_2 = dr.wrapping_add(2);
+            let dg_2 = dg.wrapping_add(2);
+            let db_2 = db.wrapping_add(2);
+            if dr_2 | dg_2 | db_2 | 3 == 3 {
+                res.push(OP_DIFF | (dr_2 << 4) | (dg_2 << 2) | db_2);
+                continue;
+            }
+            let dr_dg_8 = dr.wrapping_sub(dg).wrapping_add(8);
+            let db_dg_8 = db.wrapping_sub(dg).wrapping_add(8);
+            let dg_32 = dg.wrapping_add(32);
+            if (dg_32 | 63 == 63) && (dr_dg_8 | db_dg_8 | 15 == 15) {
+                res.extend_from_slice(&[OP_LUMA | dg_32, (dr_dg_8 << 4) | db_dg_8]);
+                continue;
+            }
+            res.extend_from_slice(&[OP_RGB, pixel[0], pixel[1], pixel[2]]);
+        }
+    }
+    if run_length > 0 {
+        res.push(OP_RUN | (run_length - 1));
+    }
+    res.extend_from_slice(&[0, 0, 0, 0, 0, 0, 0, 1]);
+    res
+}
+
+fn array_chunks<T, const N: usize>(slice: &[T]) -> &[[T; N]] {
+    let len = slice.len() / N;
+    unsafe { std::slice::from_raw_parts(slice.as_ptr() as _, len) }
+}

crates/algorithms/src/rect.rs

@@ -0,0 +1,76 @@
+pub mod region;
+
+use {
+    smallvec::SmallVec,
+    std::fmt::{Debug, Formatter},
+};
+
+pub trait Tag: Copy + Eq + Ord + Debug + Default + Sized {
+    const IS_SIGNIFICANT: bool;
+
+    fn constrain(self) -> Self;
+}
+
+#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Debug, Default)]
+pub struct NoTag;
+
+impl Tag for NoTag {
+    const IS_SIGNIFICANT: bool = false;
+
+    #[inline(always)]
+    fn constrain(self) -> Self {
+        Self
+    }
+}
+
+impl Tag for u32 {
+    const IS_SIGNIFICANT: bool = true;
+
+    #[inline(always)]
+    fn constrain(self) -> Self {
+        self & 1
+    }
+}
+
+#[derive(Copy, Clone, Eq, PartialEq, Default)]
+pub struct RectRaw<T = NoTag>
+where
+    T: Tag,
+{
+    pub x1: i32,
+    pub y1: i32,
+    pub x2: i32,
+    pub y2: i32,
+    pub tag: T,
+}
+
+impl<T> Debug for RectRaw<T>
+where
+    T: Tag,
+{
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        let mut debug = f.debug_struct("Rect");
+        debug
+            .field("x1", &self.x1)
+            .field("y1", &self.y1)
+            .field("x2", &self.x2)
+            .field("y2", &self.y2)
+            .field("width", &(self.x2 - self.x1))
+            .field("height", &(self.y2 - self.y1));
+        if T::IS_SIGNIFICANT {
+            debug.field("tag", &self.tag);
+        }
+        debug.finish()
+    }
+}
+
+impl<T> RectRaw<T>
+where
+    T: Tag,
+{
+    fn is_empty(&self) -> bool {
+        self.x1 == self.x2 || self.y1 == self.y2
+    }
+}
+
+type Container<T = NoTag> = SmallVec<[RectRaw<T>; 1]>;

crates/algorithms/src/rect/region.rs

@@ -0,0 +1,687 @@
+use {
+    crate::{
+        rect::{Container, NoTag, RectRaw, Tag},
+        windows::WindowsExt,
+    },
+    std::{cmp::Ordering, collections::BinaryHeap, marker::PhantomData, mem, ops::Deref},
+};
+
+pub fn union(left: &Container, right: &Container) -> Container {
+    op::<_, _, _, Union>(left, right)
+}
+
+pub fn subtract(left: &Container, right: &Container) -> Container {
+    op::<_, _, _, Subtract>(left, right)
+}
+
+pub fn intersect(left: &Container, right: &Container) -> Container {
+    op::<_, _, _, Intersect<NoTag>>(left, right)
+}
+
+pub fn intersect_tagged(left: &Container<u32>, right: &Container) -> Container<u32> {
+    op::<_, _, _, Intersect<u32>>(left, right)
+}
+
+struct Bands<'a, T>
+where
+    T: Tag,
+{
+    rects: &'a [RectRaw<T>],
+}
+
+#[derive(Copy, Clone)]
+struct Band<'a, T>
+where
+    T: Tag,
+{
+    rects: &'a [RectRaw<T>],
+    y1: i32,
+    y2: i32,
+}
+
+impl<'a, T> Band<'a, T>
+where
+    T: Tag,
+{
+    fn can_merge_with(&self, next: &Band<'_, T>) -> bool {
+        next.rects.len() == self.rects.len()
+            && next.y1 == self.y2
+            && next
+                .rects
+                .iter()
+                .zip(self.rects.iter())
+                .all(|(a, b)| (a.x1, a.x2, a.tag) == (b.x1, b.x2, b.tag))
+    }
+}
+
+impl<'a, T> Iterator for Bands<'a, T>
+where
+    T: Tag,
+{
+    type Item = Band<'a, T>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.rects.is_empty() {
+            return None;
+        }
+        let y1 = self.rects[0].y1;
+        let y2 = self.rects[0].y2;
+        for (pos, rect) in self.rects[1..].iter().enumerate() {
+            if rect.y1 != y1 {
+                let (res, rects) = self.rects.split_at(pos + 1);
+                self.rects = rects;
+                return Some(Band { rects: res, y1, y2 });
+            }
+        }
+        Some(Band {
+            rects: mem::replace(&mut self.rects, &[]),
+            y1,
+            y2,
+        })
+    }
+}
+
+#[inline]
+pub fn extents<T>(a: &[RectRaw<T>]) -> RectRaw
+where
+    T: Tag,
+{
+    let mut a = a.iter();
+    let mut res = match a.next() {
+        Some(a) => *a,
+        _ => return RectRaw::default(),
+    };
+    for a in a {
+        res.x1 = res.x1.min(a.x1);
+        res.y1 = res.y1.min(a.y1);
+        res.x2 = res.x2.max(a.x2);
+        res.y2 = res.y2.max(a.y2);
+    }
+    RectRaw {
+        x1: res.x1,
+        y1: res.y1,
+        x2: res.x2,
+        y2: res.y2,
+        tag: NoTag,
+    }
+}
+
+fn op<T1, T2, T3, O: Op<T1, T2, T3>>(a: &[RectRaw<T2>], b: &[RectRaw<T3>]) -> Container<T1>
+where
+    T1: Tag,
+    T2: Tag,
+    T3: Tag,
+{
+    let mut res = Container::new();
+
+    let mut prev_band_y2 = 0;
+    let mut prev_band_start = 0;
+    let mut cur_band_start;
+
+    let mut a_bands = Bands { rects: a };
+    let mut b_bands = Bands { rects: b };
+
+    let mut a_opt = a_bands.next();
+    let mut b_opt = b_bands.next();
+
+    macro_rules! fixup_new_band {
+        ($y1:expr, $y2:expr) => {{
+            if prev_band_y2 != $y1 || !coalesce(&mut res, prev_band_start, cur_band_start, $y2) {
+                prev_band_start = cur_band_start;
+            }
+            prev_band_y2 = $y2;
+        }};
+    }
+
+    macro_rules! append_nonoverlapping {
+        ($append_opt:expr, $map:ident, $a:expr, $a_opt:expr, $a_bands:expr, $b:expr) => {{
+            if $append_opt {
+                let y2 = $a.y2.min($b.y1);
+                cur_band_start = res.len();
+                res.reserve($a.rects.len());
+                for rect in $a.rects {
+                    res.push(RectRaw {
+                        x1: rect.x1,
+                        y1: $a.y1,
+                        x2: rect.x2,
+                        y2,
+                        tag: O::$map(rect.tag),
+                    });
+                }
+                fixup_new_band!($a.y1, y2);
+            }
+            if $a.y2 <= $b.y1 {
+                $a_opt = $a_bands.next();
+            } else {
+                $a.y1 = $b.y1;
+            }
+        }};
+    }
+
+    while let (Some(a), Some(b)) = (&mut a_opt, &mut b_opt) {
+        if a.y1 < b.y1 {
+            append_nonoverlapping!(O::APPEND_NON_A, map_t2_to_t1, a, a_opt, a_bands, b);
+        } else if b.y1 < a.y1 {
+            append_nonoverlapping!(O::APPEND_NON_B, map_t3_to_t1, b, b_opt, b_bands, a);
+        } else {
+            let y2 = a.y2.min(b.y2);
+            cur_band_start = res.len();
+            O::handle_band(&mut res, a.rects, b.rects, a.y1, y2);
+            if res.len() > cur_band_start {
+                fixup_new_band!(a.y1, y2);
+            }
+            if a.y2 == y2 {
+                a_opt = a_bands.next();
+            } else {
+                a.y1 = y2;
+            }
+            if b.y2 == y2 {
+                b_opt = b_bands.next();
+            } else {
+                b.y1 = y2;
+            }
+        }
+    }
+
+    macro_rules! push_trailing {
+        ($a_opt:expr, $a_bands:expr, $map:ident) => {{
+            while let Some(a) = $a_opt {
+                cur_band_start = res.len();
+                res.reserve(a.rects.len());
+                for rect in a.rects {
+                    res.push(RectRaw {
+                        x1: rect.x1,
+                        y1: a.y1,
+                        x2: rect.x2,
+                        y2: a.y2,
+                        tag: O::$map(rect.tag),
+                    });
+                }
+                fixup_new_band!(a.y1, a.y2);
+                $a_opt = $a_bands.next();
+            }
+        }};
+    }
+
+    if O::APPEND_NON_A {
+        push_trailing!(a_opt, a_bands, map_t2_to_t1);
+    }
+
+    if O::APPEND_NON_B {
+        push_trailing!(b_opt, b_bands, map_t3_to_t1);
+    }
+
+    res.shrink_to_fit();
+    res
+}
+
+fn coalesce<T>(new: &mut Container<T>, a: usize, b: usize, y2: i32) -> bool
+where
+    T: Tag,
+{
+    if new.len() - b != b - a {
+        return false;
+    }
+    let slice_a = &new[a..b];
+    let slice_b = &new[b..];
+    for (a, b) in slice_a.iter().zip(slice_b.iter()) {
+        if (a.x1, a.x2, a.tag) != (b.x1, b.x2, b.tag) {
+            return false;
+        }
+    }
+    for rect in &mut new[a..b] {
+        rect.y2 = y2;
+    }
+    new.truncate(b);
+    true
+}
+
+trait Op<T1, T2, T3>
+where
+    T1: Tag,
+    T2: Tag,
+    T3: Tag,
+{
+    const APPEND_NON_A: bool;
+    const APPEND_NON_B: bool;
+
+    fn handle_band(new: &mut Container<T1>, a: &[RectRaw<T2>], b: &[RectRaw<T3>], y1: i32, y2: i32);
+
+    fn map_t2_to_t1(tag: T2) -> T1;
+
+    fn map_t3_to_t1(tag: T3) -> T1;
+}
+
+struct Union;
+
+impl Op<NoTag, NoTag, NoTag> for Union {
+    const APPEND_NON_A: bool = true;
+    const APPEND_NON_B: bool = true;
+
+    fn handle_band(new: &mut Container, mut a: &[RectRaw], mut b: &[RectRaw], y1: i32, y2: i32) {
+        let mut x1;
+        let mut x2;
+
+        macro_rules! push {
+            () => {
+                new.push(RectRaw {
+                    x1,
+                    y1,
+                    x2,
+                    y2,
+                    tag: NoTag,
+                });
+            };
+        }
+
+        macro_rules! merge {
+            ($r:expr) => {
+                if $r.x1 <= x2 {
+                    if $r.x2 > x2 {
+                        x2 = $r.x2;
+                    }
+                } else {
+                    push!();
+                    x1 = $r.x1;
+                    x2 = $r.x2;
+                }
+            };
+        }
+
+        if a[0].x1 < b[0].x1 {
+            x1 = a[0].x1;
+            x2 = a[0].x2;
+            a = &a[1..];
+        } else {
+            x1 = b[0].x1;
+            x2 = b[0].x2;
+            b = &b[1..];
+        }
+
+        let mut a_iter = a.iter();
+        let mut b_iter = b.iter();
+
+        let mut a_opt = a_iter.next();
+        let mut b_opt = b_iter.next();
+
+        while let (Some(a), Some(b)) = (a_opt, b_opt) {
+            if a.x1 < b.x1 {
+                merge!(a);
+                a_opt = a_iter.next();
+            } else {
+                merge!(b);
+                b_opt = b_iter.next();
+            }
+        }
+
+        while let Some(a) = a_opt {
+            merge!(a);
+            a_opt = a_iter.next();
+        }
+
+        while let Some(b) = b_opt {
+            merge!(b);
+            b_opt = b_iter.next();
+        }
+
+        push!();
+    }
+
+    #[inline(always)]
+    fn map_t2_to_t1(_tag: NoTag) -> NoTag {
+        NoTag
+    }
+
+    #[inline(always)]
+    fn map_t3_to_t1(_tag: NoTag) -> NoTag {
+        NoTag
+    }
+}
+
+struct Subtract;
+
+impl Op<NoTag, NoTag, NoTag> for Subtract {
+    const APPEND_NON_A: bool = true;
+    const APPEND_NON_B: bool = false;
+
+    fn handle_band(new: &mut Container, a: &[RectRaw], b: &[RectRaw], y1: i32, y2: i32) {
+        let mut x1;
+        let mut x2;
+
+        macro_rules! push {
+            ($x2:expr) => {
+                new.push(RectRaw {
+                    x1,
+                    y1,
+                    x2: $x2,
+                    y2,
+                    tag: NoTag,
+                });
+            };
+        }
+
+        let mut a_iter = a.iter();
+        let mut b_iter = b.iter();
+
+        macro_rules! pull {
+            () => {
+                match a_iter.next() {
+                    Some(n) => {
+                        x1 = n.x1;
+                        x2 = n.x2;
+                    }
+                    _ => return,
+                }
+            };
+        }
+
+        pull!();
+
+        let mut b_opt = b_iter.next();
+
+        while let Some(b) = b_opt {
+            if b.x2 <= x1 {
+                b_opt = b_iter.next();
+            } else if b.x1 >= x2 {
+                push!(x2);
+                pull!();
+            } else {
+                if b.x1 > x1 {
+                    push!(b.x1);
+                }
+                if b.x2 < x2 {
+                    x1 = b.x2;
+                } else {
+                    pull!();
+                }
+            }
+        }
+
+        loop {
+            push!(x2);
+            pull!();
+        }
+    }
+
+    #[inline(always)]
+    fn map_t2_to_t1(_tag: NoTag) -> NoTag {
+        NoTag
+    }
+
+    #[inline(always)]
+    fn map_t3_to_t1(_tag: NoTag) -> NoTag {
+        NoTag
+    }
+}
+
+struct Intersect<T>(PhantomData<T>);
+
+impl<T> Op<T, T, NoTag> for Intersect<T>
+where
+    T: Tag,
+{
+    const APPEND_NON_A: bool = false;
+    const APPEND_NON_B: bool = false;
+
+    fn handle_band(new: &mut Container<T>, a: &[RectRaw<T>], b: &[RectRaw], y1: i32, y2: i32) {
+        let mut x1;
+        let mut x2;
+        let mut tag;
+
+        macro_rules! push {
+            ($x2:expr) => {
+                new.push(RectRaw {
+                    x1,
+                    y1,
+                    x2: $x2,
+                    y2,
+                    tag,
+                });
+            };
+        }
+
+        let mut a_iter = a.iter();
+        let mut b_iter = b.iter();
+
+        macro_rules! pull {
+            () => {
+                match a_iter.next() {
+                    Some(n) => {
+                        x1 = n.x1;
+                        x2 = n.x2;
+                        tag = n.tag;
+                    }
+                    _ => return,
+                }
+            };
+        }
+
+        pull!();
+
+        let mut b_opt = b_iter.next();
+
+        while let Some(b) = b_opt {
+            if b.x2 <= x1 {
+                b_opt = b_iter.next();
+            } else if b.x1 >= x2 {
+                pull!();
+            } else {
+                x1 = x1.max(b.x1);
+                if x2 <= b.x2 {
+                    push!(x2);
+                    pull!();
+                } else {
+                    push!(b.x2);
+                    b_opt = b_iter.next();
+                }
+            }
+        }
+    }
+
+    #[inline(always)]
+    fn map_t2_to_t1(_tag: T) -> T {
+        unreachable!()
+    }
+
+    #[inline(always)]
+    fn map_t3_to_t1(_tag: NoTag) -> T {
+        unreachable!()
+    }
+}
+
+pub fn rects_to_bands(rects_tmp: &[RectRaw]) -> Container {
+    rects_to_bands_(rects_tmp)
+}
+
+pub fn rects_to_bands_tagged(rects_tmp: &[RectRaw<u32>]) -> Container<u32> {
+    rects_to_bands_(rects_tmp)
+}
+
+#[inline(always)]
+fn rects_to_bands_<T>(rects_tmp: &[RectRaw<T>]) -> Container<T>
+where
+    T: Tag,
+{
+    #[derive(Copy, Clone)]
+    struct W<T>(RectRaw<T>)
+    where
+        T: Tag;
+    impl<T> Eq for W<T> where T: Tag {}
+    impl<T> PartialEq<Self> for W<T>
+    where
+        T: Tag,
+    {
+        fn eq(&self, other: &Self) -> bool {
+            self.0 == other.0
+        }
+    }
+    impl<T> PartialOrd<Self> for W<T>
+    where
+        T: Tag,
+    {
+        fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+            Some(self.cmp(other))
+        }
+    }
+    impl<T> Ord for W<T>
+    where
+        T: Tag,
+    {
+        fn cmp(&self, other: &Self) -> Ordering {
+            self.0
+                .y1
+                .cmp(&other.0.y1)
+                .then_with(|| self.0.x1.cmp(&other.0.x1))
+                .then_with(|| self.0.tag.cmp(&other.0.tag))
+                .reverse()
+        }
+    }
+    impl<T> Deref for W<T>
+    where
+        T: Tag,
+    {
+        type Target = RectRaw<T>;
+        fn deref(&self) -> &Self::Target {
+            &self.0
+        }
+    }
+
+    let ys = {
+        let mut tmp: Vec<_> = rects_tmp.iter().flat_map(|r| [r.y1, r.y2]).collect();
+        tmp.sort_unstable();
+        let mut last = None;
+        let mut res = vec![];
+        for y in tmp {
+            if Some(y) != last {
+                last = Some(y);
+                res.push(y);
+            }
+        }
+        res
+    };
+
+    let mut rects = BinaryHeap::with_capacity(rects_tmp.len());
+    for rect in rects_tmp.iter().copied() {
+        if !rect.is_empty() {
+            rects.push(W(rect));
+        }
+    }
+
+    let mut res = Container::new();
+
+    for &[y1, y2] in ys.array_windows_ext::<2>() {
+        #[expect(clippy::never_loop)]
+        loop {
+            macro_rules! check_rect {
+                ($rect:expr) => {{
+                    if $rect.y1 != y1 {
+                        break;
+                    }
+                    rects.pop();
+                    if y2 < $rect.y2 {
+                        $rect.0.y1 = y2;
+                        rects.push($rect);
+                    }
+                }};
+            }
+            if let Some(mut rect) = rects.peek().copied() {
+                check_rect!(rect);
+                let mut x1 = rect.x1;
+                let mut x2 = rect.x2;
+                let mut tag: T = rect.tag;
+                while let Some(mut rect) = rects.peek().copied() {
+                    check_rect!(rect);
+                    if rect.x1 > x2 || (rect.tag != tag && rect.x1 == x2) {
+                        res.push(RectRaw {
+                            x1,
+                            x2,
+                            y1,
+                            y2,
+                            tag: tag.constrain(),
+                        });
+                        x1 = rect.x1;
+                        x2 = rect.x2;
+                        tag = rect.tag;
+                    } else {
+                        if rect.tag == tag {
+                            x2 = x2.max(rect.x2);
+                        } else if rect.tag > tag {
+                            if rect.x2 > x2 {
+                                rect.0.x1 = x2;
+                                rect.0.y1 = y1;
+                                rect.0.y2 = y2;
+                                rects.push(rect);
+                            }
+                        } else {
+                            if x2 > rect.x2 {
+                                rects.push(W(RectRaw {
+                                    x1: rect.x2,
+                                    y1,
+                                    x2,
+                                    y2,
+                                    tag,
+                                }));
+                            }
+                            res.push(RectRaw {
+                                x1,
+                                y1,
+                                x2: rect.x1,
+                                y2,
+                                tag: tag.constrain(),
+                            });
+                            x1 = rect.x1;
+                            x2 = rect.x2;
+                            tag = rect.tag;
+                        }
+                    }
+                }
+                res.push(RectRaw {
+                    x1,
+                    x2,
+                    y1,
+                    y2,
+                    tag: tag.constrain(),
+                });
+            }
+            break;
+        }
+    }
+
+    let mut needs_merge = false;
+    let mut num_elements = res.len();
+    let mut bands = Bands { rects: &res }.peekable();
+    while let Some(band) = bands.next() {
+        let next = match bands.peek() {
+            Some(next) => next,
+            _ => break,
+        };
+        if band.can_merge_with(next) {
+            needs_merge = true;
+            num_elements -= band.rects.len();
+        }
+    }
+
+    if !needs_merge {
+        res.shrink_to_fit();
+        return res;
+    }
+
+    let mut merged = Container::with_capacity(num_elements);
+    let mut bands = Bands { rects: &res }.peekable();
+    while let Some(mut band) = bands.next() {
+        while let Some(next) = bands.peek() {
+            if band.can_merge_with(next) {
+                band.y2 = next.y2;
+                bands.next();
+            } else {
+                break;
+            }
+        }
+        for mut rect in band.rects.iter().copied() {
+            rect.y2 = band.y2;
+            merged.push(rect);
+        }
+    }
+
+    merged
+}

crates/algorithms/src/windows.rs

@@ -0,0 +1,38 @@
+pub trait WindowsExt<T> {
+    type Windows<'a, const N: usize>: Iterator<Item = &'a [T; N]>
+    where
+        Self: 'a,
+        T: 'a;
+
+    fn array_windows_ext<'a, const N: usize>(&'a self) -> Self::Windows<'a, N>;
+}
+
+impl<T> WindowsExt<T> for [T] {
+    type Windows<'a, const N: usize>
+        = WindowsIter<'a, T, N>
+    where
+        T: 'a;
+
+    fn array_windows_ext<'a, const N: usize>(&'a self) -> Self::Windows<'a, N> {
+        WindowsIter { slice: self }
+    }
+}
+
+pub struct WindowsIter<'a, T, const N: usize> {
+    slice: &'a [T],
+}
+
+impl<'a, T, const N: usize> Iterator for WindowsIter<'a, T, N> {
+    type Item = &'a [T; N];
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.slice.len() < N {
+            return None;
+        }
+        let res = unsafe { &*self.slice.as_ptr().cast::<[T; N]>() };
+        if N > 0 {
+            self.slice = &self.slice[1..];
+        }
+        Some(res)
+    }
+}