Added App::clear_color() that apps can use to specify background color

egui_glium/src/backend.rs

@@ -111,7 +111,13 @@ pub fn run(mut storage: Box<dyn egui::app::Storage>, mut app: Box<dyn App>) -> !
 
             let frame_time = (Instant::now() - egui_start).as_secs_f64() as f32;
             previous_frame_time = Some(frame_time);
-            painter.paint_jobs(&display, ctx.pixels_per_point(), paint_jobs, &ctx.texture());
+            painter.paint_jobs(
+                &display,
+                ctx.pixels_per_point(),
+                app.clear_color(),
+                paint_jobs,
+                &ctx.texture(),
+            );
 
             {
                 let egui::app::AppOutput {

egui_glium/src/painter.rs

@@ -126,6 +126,7 @@ impl Painter {
         &mut self,
         display: &glium::Display,
         pixels_per_point: f32,
+        clear_color: egui::Rgba,
         jobs: PaintJobs,
         egui_texture: &egui::Texture,
     ) {
@@ -133,7 +134,13 @@ impl Painter {
         self.upload_pending_user_textures(display);
 
         let mut target = display.draw();
-        target.clear_color(0.0, 0.0, 0.0, 0.0);
+        // Verified to be gamma-correct.
+        target.clear_color(
+            clear_color[0],
+            clear_color[1],
+            clear_color[2],
+            clear_color[3],
+        );
         for (clip_rect, triangles) in jobs {
             self.paint_job(
                 &mut target,