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Don't report CoreGraphics as supporting premultiplied alpha #356

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Merged
madsmtm merged 1 commit into from
Apr 21, 2026
Merged

Don't report CoreGraphics as supporting premultiplied alpha #356

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8 changes: 6 additions & 2 deletions src/backends/cg.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -284,8 +284,12 @@ impl<D: HasDisplayHandle, W: HasWindowHandle> SurfaceInterface<D, W> for CGImpl<
}

#[inline]
fn supports_alpha_mode(&self, _alpha_mode: AlphaMode) -> bool {
true
fn supports_alpha_mode(&self, alpha_mode: AlphaMode) -> bool {
// Premultiplied doesn't seem to work, at least not with transparent windows.
matches!(
alpha_mode,
AlphaMode::Ignored | AlphaMode::Opaque | AlphaMode::Postmultiplied
)
}

fn configure(
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3 changes: 1 addition & 2 deletions src/lib.rs
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Expand Up @@ -641,11 +641,10 @@ pub enum AlphaMode {
/// ## Platform Dependent Behavior
///
/// - Wayland and DRM/KMS: Supported.
/// - macOS/iOS: Supported, but currently doesn't work with additive values (maybe only as the
/// root layer?). Will be fixed by <https://github.com/rust-windowing/softbuffer/pull/329>.
/// - Web: Not yet supported (TODO `ImageBitmap`).
/// - Android, Orbital, Windows and X11: Not supported (yet unknown if they can be, feel
/// free to open an issue about it).
/// - macOS/iOS: Not supported (doesn't seem to work with additive values).
#[doc(alias = "Associated")]
Premultiplied,
/// The non-alpha channels are not expected to already be multiplied by the alpha channel;
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