Fix color blending for user textures

src/egui.wgsl

@@ -45,7 +45,9 @@ var s_egui: sampler;
 
 [[stage(fragment)]]
 fn fs_main(in: VertexOutput) -> [[location(0)]] vec4<f32> {
-    let color = in.color * textureSample(t_egui, s_egui, in.uv);
+    let texture_color = textureSample(t_egui, s_egui, in.uv);
+    // This assumes that colors are premultiplied but texture images are not.
+    let color = in.color * vec4<f32>(texture_color.rgb * texture_color.a, texture_color.a);
 
     return color;
 }

src/egui_node.rs

@@ -385,26 +385,29 @@ impl Node for EguiNode {
     }
 }
 
-pub fn as_color_image(image: egui::ImageData) -> egui::ColorImage {
+pub(crate) fn as_color_image(image: egui::ImageData) -> egui::ColorImage {
     match image {
         egui::ImageData::Color(image) => image,
         egui::ImageData::Alpha(image) => alpha_image_as_color_image(&image),
     }
 }
 
-pub fn alpha_image_as_color_image(image: &egui::AlphaImage) -> egui::ColorImage {
+fn alpha_image_as_color_image(image: &egui::AlphaImage) -> egui::ColorImage {
     let gamma = 1.0;
     egui::ColorImage {
         size: image.size,
         pixels: image.srgba_pixels(gamma).collect(),
     }
 }
 
-pub fn color_image_as_bevy_image(egui_image: &egui::ColorImage) -> Image {
+pub(crate) fn color_image_as_bevy_image(egui_image: &egui::ColorImage) -> Image {
     let pixels = egui_image
         .pixels
         .iter()
-        .flat_map(|color| color.to_array())
+        // We unmultiply Egui textures to premultiply them later in the fragment shader.
+        // As user textures loaded as Bevy assets are not premultiplied (and there seems to be no
+        // convenient way to convert them to premultiplied ones), we do the this with Egui ones.
+        .flat_map(|color| color.to_srgba_unmultiplied())
         .collect();
 
     Image::new(