From 6aaefc05469649edbf39d90d2a570eef76d8a41e Mon Sep 17 00:00:00 2001
From: Kirill Chibisov <contact@kchibisov.com>
Date: Tue, 30 Jan 2024 18:03:21 +0400
Subject: [PATCH 1/2] On Wayland, pre-multiply alpha for custom cursor

Fixes: #3360
---
 examples/custom_cursors.rs                      |   3 ++-
 examples/data/gradient.png                      | Bin 0 -> 229 bytes
 src/platform_impl/linux/wayland/types/cursor.rs |  15 +++++++++------
 3 files changed, 11 insertions(+), 7 deletions(-)
 create mode 100644 examples/data/gradient.png

diff --git a/examples/custom_cursors.rs b/examples/custom_cursors.rs
index fda157ff5a..0d0fb4469f 100644
--- a/examples/custom_cursors.rs
+++ b/examples/custom_cursors.rs
@@ -56,6 +56,7 @@ fn main() -> Result<(), impl std::error::Error> {
     let custom_cursors = [
         decode_cursor(include_bytes!("data/cross.png"), &event_loop),
         decode_cursor(include_bytes!("data/cross2.png"), &event_loop),
+        decode_cursor(include_bytes!("data/gradient.png"), &event_loop),
     ];
 
     event_loop.run(move |event, _elwt| match event {
@@ -72,7 +73,7 @@ fn main() -> Result<(), impl std::error::Error> {
                 Key::Character("1") => {
                     log::debug!("Setting cursor to {:?}", cursor_idx);
                     window.set_cursor(custom_cursors[cursor_idx].clone());
-                    cursor_idx = (cursor_idx + 1) % 2;
+                    cursor_idx = (cursor_idx + 1) % 3;
                 }
                 Key::Character("2") => {
                     log::debug!("Setting cursor icon to default");
diff --git a/examples/data/gradient.png b/examples/data/gradient.png
new file mode 100644
index 0000000000000000000000000000000000000000..41ce610e66221b0803d20b0dcca6f9215745ac3b
GIT binary patch
literal 229
zcmeAS@N?(olHy`uVBq!ia0vp^0wB!61|;P_|4#%`Ydl>XLo80uophJ$kO7aI|Ep(n
z9<?fTD0IBv_`P1|aqnf5CH7JpCYhgAE!V!-#G!D2O`?%=Mx$*33*P}w3uf^LTz49*
zKX}ymo{2kocK+IKmmIT14i@`zFQ$KsX1uy~o@I;CA%UI`Z)6j{x(CPJ+Zok-<I~oo
z3QXHg3mKQNFA_h~FipWrwQy7V%l2=Z`9(NAo{HAwTu%ykb)Y+gpINhH>Hm@k-Dg%N
d=dCrYVq|Yu-*G2OKmq7(22WQ%mvv4FO#tkjTQ&dy

literal 0
HcmV?d00001

diff --git a/src/platform_impl/linux/wayland/types/cursor.rs b/src/platform_impl/linux/wayland/types/cursor.rs
index 4af996f6f3..c1a0c2613a 100644
--- a/src/platform_impl/linux/wayland/types/cursor.rs
+++ b/src/platform_impl/linux/wayland/types/cursor.rs
@@ -37,12 +37,15 @@ impl CustomCursor {
             )
             .unwrap();
 
-        for (canvas_chunk, rgba_chunk) in canvas.chunks_exact_mut(4).zip(image.rgba.chunks_exact(4))
-        {
-            canvas_chunk[0] = rgba_chunk[2];
-            canvas_chunk[1] = rgba_chunk[1];
-            canvas_chunk[2] = rgba_chunk[0];
-            canvas_chunk[3] = rgba_chunk[3];
+        for (canvas_chunk, rgba) in canvas.chunks_exact_mut(4).zip(image.rgba.chunks_exact(4)) {
+            // Alpha in buffer is premultiplied.
+            let alpha = rgba[3] as f32 / 255.;
+            let r = (rgba[0] as f32 * alpha) as u32;
+            let g = (rgba[1] as f32 * alpha) as u32;
+            let b = (rgba[2] as f32 * alpha) as u32;
+            let color = ((rgba[3] as u32) << 24) + (r << 16) + (g << 8) + b;
+            let array: &mut [u8; 4] = canvas_chunk.try_into().unwrap();
+            *array = color.to_le_bytes();
         }
 
         CustomCursor {

From f2fdb12e1045bb4e118cb4fd72edd991c3508691 Mon Sep 17 00:00:00 2001
From: Kirill Chibisov <contact@kchibisov.com>
Date: Tue, 30 Jan 2024 18:25:05 +0400
Subject: [PATCH 2/2] Specify that alpha channel is not premultiplied

---
 src/cursor.rs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/cursor.rs b/src/cursor.rs
index e1ed4622dc..b519b579fb 100644
--- a/src/cursor.rs
+++ b/src/cursor.rs
@@ -83,6 +83,8 @@ pub struct CustomCursor {
 
 impl CustomCursor {
     /// Creates a new cursor from an rgba buffer.
+    ///
+    /// The alpha channel is assumed to be **not** premultiplied.
     pub fn from_rgba(
         rgba: impl Into<Vec<u8>>,
         width: u16,