Fix alpha mode configuration in `iced_wgpu`

1 files changed, 40 insertions, 20 deletions

diff --git a/wgpu/src/window/compositor.rs b/wgpu/src/window/compositor.rs
index 58f3f654..3e329362 100644
--- a/wgpu/src/window/compositor.rs
+++ b/wgpu/src/window/compositor.rs
@@ -15,6 +15,7 @@ pub struct Compositor {
     device: wgpu::Device,
     queue: wgpu::Queue,
     format: wgpu::TextureFormat,
+    alpha_mode: wgpu::CompositeAlphaMode,
 }
 
 impl Compositor {
@@ -61,25 +62,43 @@ impl Compositor {
 
         log::info!("Selected: {:#?}", adapter.get_info());
 
-        let format = compatible_surface.as_ref().and_then(|surface| {
-            let capabilities = surface.get_capabilities(&adapter);
-
-            let mut formats = capabilities.formats.iter().copied();
-
-            let format = if color::GAMMA_CORRECTION {
-                formats.find(wgpu::TextureFormat::is_srgb)
-            } else {
-                formats.find(|format| !wgpu::TextureFormat::is_srgb(format))
-            };
-
-            format.or_else(|| {
-                log::warn!("No format found!");
-
-                capabilities.formats.first().copied()
-            })
-        })?;
-
-        log::info!("Selected format: {format:?}");
+        let (format, alpha_mode) =
+            compatible_surface.as_ref().and_then(|surface| {
+                let capabilities = surface.get_capabilities(&adapter);
+
+                let mut formats = capabilities.formats.iter().copied();
+
+                let format = if color::GAMMA_CORRECTION {
+                    formats.find(wgpu::TextureFormat::is_srgb)
+                } else {
+                    formats.find(|format| !wgpu::TextureFormat::is_srgb(format))
+                };
+
+                let format = format.or_else(|| {
+                    log::warn!("No format found!");
+
+                    capabilities.formats.first().copied()
+                });
+
+                let alphas = capabilities.alpha_modes;
+                let preferred_alpha = if alphas
+                    .contains(&wgpu::CompositeAlphaMode::PostMultiplied)
+                {
+                    wgpu::CompositeAlphaMode::PostMultiplied
+                } else if alphas
+                    .contains(&wgpu::CompositeAlphaMode::PreMultiplied)
+                {
+                    wgpu::CompositeAlphaMode::PreMultiplied
+                } else {
+                    wgpu::CompositeAlphaMode::Auto
+                };
+
+                format.zip(Some(preferred_alpha))
+            })?;
+
+        log::info!(
+            "Selected format: {format:?} with alpha mode: {alpha_mode:?}"
+        );
 
         #[cfg(target_arch = "wasm32")]
         let limits = [wgpu::Limits::downlevel_webgl2_defaults()
@@ -120,6 +139,7 @@ impl Compositor {
             device,
             queue,
             format,
+            alpha_mode,
         })
     }
 
@@ -249,7 +269,7 @@ impl graphics::Compositor for Compositor {
                 present_mode: self.settings.present_mode,
                 width,
                 height,
-                alpha_mode: wgpu::CompositeAlphaMode::Auto,
+                alpha_mode: self.alpha_mode,
                 view_formats: vec![],
                 desired_maximum_frame_latency: 2,
             },