Support transparent windows in vger

Author: jrmoulton

examples/widget-gallery/src/main.rs

@@ -173,5 +173,10 @@ fn app_view() -> impl IntoView {
 }
 
 fn main() {
-    floem::launch(app_view);
+    floem::Application::new()
+        .window(
+            |_| app_view(),
+            Some(WindowConfig::default().with_transparent(true)),
+        )
+        .run();
 }

tiny_skia/src/lib.rs

@@ -583,7 +583,7 @@ impl<W: raw_window_handle::HasWindowHandle + raw_window_handle::HasDisplayHandle
     fn begin(&mut self, _capture: bool) {
         assert!(self.layers.len() == 1);
         let first_layer = self.layers.last_mut().unwrap();
-        first_layer.pixmap.fill(tiny_skia::Color::WHITE);
+        first_layer.pixmap.fill(tiny_skia::Color::TRANSPARENT);
         first_layer.clip = None;
         first_layer.transform = Affine::IDENTITY;
     }
@@ -665,7 +665,8 @@ impl<W: raw_window_handle::HasWindowHandle + raw_window_handle::HasDisplayHandle
         {
             *out_pixel = ((pixel.red() as u32) << 16)
                 | ((pixel.green() as u32) << 8)
-                | (pixel.blue() as u32);
+                | (pixel.blue() as u32)
+                | ((pixel.alpha() as u32) << 24);
         }
 
         buffer

vello/src/lib.rs

@@ -84,7 +84,7 @@ impl VelloRenderer {
             width,
             height,
             present_mode: wgpu::PresentMode::Fifo,
-            alpha_mode: wgpu::CompositeAlphaMode::Auto,
+            alpha_mode: wgpu::CompositeAlphaMode::PostMultiplied,
             view_formats: vec![],
             desired_maximum_frame_latency: 2,
         };

vger/src/lib.rs

@@ -16,7 +16,10 @@ use peniko::{
     kurbo::{Affine, Point, Rect, Shape},
     BrushRef, Color, GradientKind,
 };
-use wgpu::{Device, DeviceType, Queue, StoreOp, Surface, SurfaceConfiguration, TextureFormat};
+use wgpu::{
+    CompositeAlphaMode, Device, DeviceType, Queue, StoreOp, Surface, SurfaceConfiguration,
+    TextureFormat,
+};
 
 pub struct VgerRenderer {
     device: Arc<Device>,
@@ -74,14 +77,27 @@ impl VgerRenderer {
             .into_iter()
             .find(|it| matches!(it, TextureFormat::Rgba8Unorm | TextureFormat::Bgra8Unorm))
             .ok_or_else(|| anyhow::anyhow!("surface should support Rgba8Unorm or Bgra8Unorm"))?;
+        let alpha_mode = if surface_caps
+            .alpha_modes
+            .contains(&CompositeAlphaMode::PreMultiplied)
+        {
+            CompositeAlphaMode::PreMultiplied
+        } else if surface_caps
+            .alpha_modes
+            .contains(&CompositeAlphaMode::PostMultiplied)
+        {
+            CompositeAlphaMode::PostMultiplied
+        } else {
+            CompositeAlphaMode::Auto
+        };
 
         let config = wgpu::SurfaceConfiguration {
             usage: wgpu::TextureUsages::RENDER_ATTACHMENT,
             format: texture_format,
             width,
             height,
             present_mode: wgpu::PresentMode::Fifo,
-            alpha_mode: wgpu::CompositeAlphaMode::Auto,
+            alpha_mode,
             view_formats: vec![],
             desired_maximum_frame_latency: 2,
         };