Add custom window background/clear color (incl. transparency) support, fixes #272

wgpu would currently ignore the alpha: https://github.com/gfx-rs/wgpu/issues/687

glow (and naively patched wgpu) requires premultiplied alpha, so if you don't
multiply the RGB by the A right now, the semi-transparent color would be wrong
(too bright).

winit with_transparent doesn't seem necessary.

2 files changed, 12 insertions, 2 deletions

diff --git a/glow/src/settings.rs b/glow/src/settings.rs
index dce30029..68fde714 100644
--- a/glow/src/settings.rs
+++ b/glow/src/settings.rs
@@ -1,10 +1,11 @@
 //! Configure a renderer.
 pub use iced_graphics::Antialiasing;
+pub use iced_native::Color;
 
 /// The settings of a [`Renderer`].
 ///
 /// [`Renderer`]: ../struct.Renderer.html
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[derive(Debug, Clone, Copy, PartialEq)]
 pub struct Settings {
     /// The bytes of the font that will be used by default.
     ///
@@ -13,6 +14,9 @@ pub struct Settings {
 
     /// The antialiasing strategy that will be used for triangle primitives.
     pub antialiasing: Option<Antialiasing>,
+
+    /// The color that will be used to clear the window surface.
+    pub background_color: Color,
 }
 
 impl Default for Settings {
@@ -20,6 +24,7 @@ impl Default for Settings {
         Settings {
             default_font: None,
             antialiasing: None,
+            background_color: Color::WHITE,
         }
     }
 }
diff --git a/glow/src/window/compositor.rs b/glow/src/window/compositor.rs
index 2f504ff7..c93191b0 100644
--- a/glow/src/window/compositor.rs
+++ b/glow/src/window/compositor.rs
@@ -21,7 +21,12 @@ impl iced_graphics::window::GLCompositor for Compositor {
     ) -> (Self, Self::Renderer) {
         let gl = glow::Context::from_loader_function(loader_function);
 
-        gl.clear_color(1.0, 1.0, 1.0, 1.0);
+        gl.clear_color(
+            settings.background_color.r,
+            settings.background_color.g,
+            settings.background_color.b,
+            settings.background_color.a,
+        );
 
         // Enable auto-conversion from/to sRGB
         gl.enable(glow::FRAMEBUFFER_SRGB);