fix coloured text wrongly premultiplying alpha twice

crates/yakui-core/src/paint/texture.rs

@@ -37,6 +37,10 @@ pub enum TextureFormat {
     /// color channels are sRGB-encoded.
     Rgba8Srgb,
 
+    /// Red, green, blue, and alpha channels, each represented as a `u8`. The
+    /// color channels are sRGB-encoded and premultiplied by the alpha.
+    Rgba8SrgbPremultiplied,
+
     /// A single color channel represented as a `u8`.
     R8,
 }

crates/yakui-vulkan/src/vulkan_texture.rs

@@ -180,6 +180,7 @@ impl VulkanTexture {
 fn get_format(yakui_format: yakui::paint::TextureFormat) -> vk::Format {
     match yakui_format {
         yakui::paint::TextureFormat::Rgba8Srgb => vk::Format::R8G8B8A8_SRGB,
+        yakui::paint::TextureFormat::Rgba8SrgbPremultiplied => vk::Format::R8G8B8A8_SRGB,
         yakui::paint::TextureFormat::R8 => vk::Format::R8_UNORM,
         _ => panic!("Unsupported texture format: {yakui_format:?}"),
     }

crates/yakui-wgpu/src/texture.rs

@@ -109,6 +109,11 @@ fn data_layout(format: TextureFormat, size: UVec2) -> wgpu::ImageDataLayout {
             bytes_per_row: Some(4 * size.x),
             rows_per_image: Some(size.y),
         },
+        TextureFormat::Rgba8SrgbPremultiplied => wgpu::ImageDataLayout {
+            offset: 0,
+            bytes_per_row: Some(4 * size.x),
+            rows_per_image: Some(size.y),
+        },
         TextureFormat::R8 => wgpu::ImageDataLayout {
             offset: 0,
             bytes_per_row: Some(size.x),
@@ -121,6 +126,7 @@ fn data_layout(format: TextureFormat, size: UVec2) -> wgpu::ImageDataLayout {
 fn wgpu_format(format: TextureFormat) -> wgpu::TextureFormat {
     match format {
         TextureFormat::Rgba8Srgb => wgpu::TextureFormat::Rgba8UnormSrgb,
+        TextureFormat::Rgba8SrgbPremultiplied => wgpu::TextureFormat::Rgba8UnormSrgb,
         TextureFormat::R8 => wgpu::TextureFormat::R8Unorm,
         _ => panic!("Unsupported texture format {format:?}"),
     }
@@ -157,6 +163,7 @@ fn premultiply_alpha(texture: &Texture) -> Cow<'_, Texture> {
 
             Cow::Owned(texture)
         }
+        TextureFormat::Rgba8SrgbPremultiplied => Cow::Borrowed(texture),
         TextureFormat::R8 => Cow::Borrowed(texture),
         _ => Cow::Borrowed(texture),
     }

crates/yakui-widgets/src/text_renderer.rs

@@ -23,7 +23,7 @@ impl Kind {
     fn texture_format(self) -> TextureFormat {
         match self {
             Kind::Mask => TextureFormat::R8,
-            Kind::Color => TextureFormat::Rgba8Srgb,
+            Kind::Color => TextureFormat::Rgba8SrgbPremultiplied,
         }
     }
 }