Notify window before presentation

graphics/src/compositor.rs

@@ -80,6 +80,7 @@ pub trait Compositor: Sized {
         viewport: &Viewport,
         background_color: Color,
         overlay: &[T],
+        on_pre_present: impl FnOnce(),
     ) -> Result<(), SurfaceError>;
 
     /// Screenshots the current [`Renderer`] primitives to an offscreen texture, and returns the bytes of
@@ -193,6 +194,7 @@ impl Compositor for () {
         _viewport: &Viewport,
         _background_color: Color,
         _overlay: &[T],
+        _on_pre_present: impl FnOnce(),
     ) -> Result<(), SurfaceError> {
         Ok(())
     }

renderer/src/fallback.rs

@@ -322,6 +322,7 @@ where
         viewport: &graphics::Viewport,
         background_color: Color,
         overlay: &[T],
+        on_pre_present: impl FnOnce(),
     ) -> Result<(), compositor::SurfaceError> {
         match (self, renderer, surface) {
             (
@@ -334,6 +335,7 @@ where
                 viewport,
                 background_color,
                 overlay,
+                on_pre_present,
             ),
             (
                 Self::Secondary(compositor),
@@ -345,6 +347,7 @@ where
                 viewport,
                 background_color,
                 overlay,
+                on_pre_present,
             ),
             _ => unreachable!(),
         }

tiny_skia/src/window/compositor.rs

@@ -114,8 +114,16 @@ impl crate::graphics::Compositor for Compositor {
         viewport: &Viewport,
         background_color: Color,
         overlay: &[T],
+        on_pre_present: impl FnOnce(),
     ) -> Result<(), compositor::SurfaceError> {
-        present(renderer, surface, viewport, background_color, overlay)
+        present(
+            renderer,
+            surface,
+            viewport,
+            background_color,
+            overlay,
+            on_pre_present,
+        )
     }
 
     fn screenshot<T: AsRef<str>>(
@@ -146,6 +154,7 @@ pub fn present<T: AsRef<str>>(
     viewport: &Viewport,
     background_color: Color,
     overlay: &[T],
+    on_pre_present: impl FnOnce(),
 ) -> Result<(), compositor::SurfaceError> {
     let physical_size = viewport.physical_size();
 
@@ -206,6 +215,7 @@ pub fn present<T: AsRef<str>>(
         overlay,
     );
 
+    on_pre_present();
     buffer.present().map_err(|_| compositor::SurfaceError::Lost)
 }
 

wgpu/src/window/compositor.rs

@@ -221,6 +221,7 @@ pub fn present<T: AsRef<str>>(
     viewport: &Viewport,
     background_color: Color,
     overlay: &[T],
+    on_pre_present: impl FnOnce(),
 ) -> Result<(), compositor::SurfaceError> {
     match surface.get_current_texture() {
         Ok(frame) => {
@@ -249,6 +250,7 @@ pub fn present<T: AsRef<str>>(
             let _ = compositor.engine.submit(&compositor.queue, encoder);
 
             // Present the frame
+            on_pre_present();
             frame.present();
 
             Ok(())
@@ -365,8 +367,17 @@ impl graphics::Compositor for Compositor {
         viewport: &Viewport,
         background_color: Color,
         overlay: &[T],
+        on_pre_present: impl FnOnce(),
     ) -> Result<(), compositor::SurfaceError> {
-        present(self, renderer, surface, viewport, background_color, overlay)
+        present(
+            self,
+            renderer,
+            surface,
+            viewport,
+            background_color,
+            overlay,
+            on_pre_present,
+        )
     }
 
     fn screenshot<T: AsRef<str>>(

winit/src/program.rs

@@ -892,6 +892,7 @@ async fn run_instance<P, C>(
                             window.state.viewport(),
                             window.state.background_color(),
                             &debug.overlay(),
+                            || window.raw.pre_present_notify(),
                         ) {
                             Ok(()) => {
                                 debug.render_finished();