Optimizations for Winit Examples. (#686)

This optimizes examples by using `ControlFlow::Wait` instead of
`ControlFlow::Poll`. This fix was found by Micah Johnston, and this PR
implements it in both "simple" and "with_winit" examples.

- "simple" now runs at 0.1-0.2% CPU usage.
- "with_winit" now runs at 1.0-1.8%.

[You can check more info about it
here](https://xi.zulipchat.com/#narrow/stream/147921-general/topic/I've.20made.20a.20Vello.20game.20engine.20to.20prove.20that.20i.20was.20wrong.2E/near/468637207)

---------

Co-authored-by: Daniel McNab <[email protected]>

examples/simple/src/main.rs

@@ -11,7 +11,7 @@ use vello::{AaConfig, DebugLayers, Renderer, RendererOptions, Scene};
 use winit::application::ApplicationHandler;
 use winit::dpi::LogicalSize;
 use winit::event::*;
-use winit::event_loop::{ActiveEventLoop, ControlFlow, EventLoop};
+use winit::event_loop::{ActiveEventLoop, EventLoop};
 use winit::window::Window;
 
 use vello::wgpu;
@@ -74,15 +74,12 @@ impl<'s> ApplicationHandler for SimpleVelloApp<'s> {
 
         // Save the Window and Surface to a state variable
         self.state = RenderState::Active(ActiveRenderState { window, surface });
-
-        event_loop.set_control_flow(ControlFlow::Poll);
     }
 
-    fn suspended(&mut self, event_loop: &ActiveEventLoop) {
+    fn suspended(&mut self, _event_loop: &ActiveEventLoop) {
         if let RenderState::Active(state) = &self.state {
             self.state = RenderState::Suspended(Some(state.window.clone()));
         }
-        event_loop.set_control_flow(ControlFlow::Wait);
     }
 
     fn window_event(
@@ -109,7 +106,6 @@ impl<'s> ApplicationHandler for SimpleVelloApp<'s> {
             WindowEvent::Resized(size) => {
                 self.context
                     .resize_surface(&mut render_state.surface, size.width, size.height);
-                render_state.window.request_redraw();
             }
 
             // This is where all the rendering happens

examples/with_winit/src/lib.rs

@@ -14,7 +14,6 @@ use std::time::Instant;
 use web_time::Instant;
 use winit::application::ApplicationHandler;
 use winit::event::*;
-use winit::event_loop::ControlFlow;
 use winit::keyboard::*;
 
 #[cfg(all(feature = "wgpu-profiler", not(target_arch = "wasm32")))]
@@ -226,7 +225,6 @@ impl<'s> ApplicationHandler<UserEvent> for VelloApp<'s> {
             });
             Some(render_state)
         };
-        event_loop.set_control_flow(ControlFlow::Poll);
     }
 
     fn window_event(
@@ -443,6 +441,8 @@ impl<'s> ApplicationHandler<UserEvent> for VelloApp<'s> {
                 let _rendering_span = tracing::trace_span!("Actioning Requested Redraw").entered();
                 let encoding_span = tracing::trace_span!("Encoding scene").entered();
 
+                render_state.window.request_redraw();
+
                 let Some(RenderState { surface, window }) = &self.state else {
                     return;
                 };
@@ -633,14 +633,13 @@ impl<'s> ApplicationHandler<UserEvent> for VelloApp<'s> {
         }
     }
 
-    fn suspended(&mut self, event_loop: &winit::event_loop::ActiveEventLoop) {
+    fn suspended(&mut self, _event_loop: &winit::event_loop::ActiveEventLoop) {
         log::info!("Suspending");
         #[cfg(not(target_arch = "wasm32"))]
         // When we suspend, we need to remove the `wgpu` Surface
         if let Some(render_state) = self.state.take() {
             self.cached_window = Some(render_state.window);
         }
-        event_loop.set_control_flow(ControlFlow::Wait);
     }
 }