Desktop: Only rerender the UI if it has changed (#3688)

* Only rerender ui if it has changed

* Don't immedeatly request new frame at the end of the event loop

* Request redraw after ui update

* Always request redraw after timeout

* Fix setting control flow in all cases

* Remove comment

---------

Co-authored-by: Timon <me@timon.zip>

desktop/src/app.rs

@@ -6,7 +6,7 @@ use std::thread;
 use std::time::{Duration, Instant};
 use winit::application::ApplicationHandler;
 use winit::dpi::{PhysicalPosition, PhysicalSize};
-use winit::event::{ButtonSource, ElementState, MouseButton, WindowEvent};
+use winit::event::{ButtonSource, ElementState, MouseButton, StartCause, WindowEvent};
 use winit::event_loop::{ActiveEventLoop, ControlFlow, EventLoop};
 use winit::window::WindowId;
 
@@ -260,6 +260,9 @@ impl App {
 				if let Some(render_state) = &mut self.render_state {
 					render_state.set_overlays_scene(scene);
 				}
+				if let Some(window) = &self.window {
+					window.request_redraw();
+				}
 			}
 			DesktopFrontendMessage::PersistenceWriteDocument { id, document } => {
 				self.persistent_data.write_document(id, document);
@@ -632,10 +635,17 @@ impl ApplicationHandler for App {
 		}
 	}
 
+	fn new_events(&mut self, event_loop: &dyn ActiveEventLoop, cause: winit::event::StartCause) {
+		if let StartCause::ResumeTimeReached { .. } = cause
+			&& let Some(window) = &self.window
+		{
+			window.request_redraw();
+		}
+	}
+
 	fn about_to_wait(&mut self, event_loop: &dyn ActiveEventLoop) {
 		// Set a timeout in case we miss any cef schedule requests
-		let timeout = Instant::now() + Duration::from_millis(10);
-		let wait_until = timeout.min(self.cef_schedule.unwrap_or(timeout));
+		let mut wait_until = Instant::now() + Duration::from_millis(10);
 		if let Some(schedule) = self.cef_schedule
 			&& schedule < Instant::now()
 		{
@@ -644,11 +654,9 @@ impl ApplicationHandler for App {
 			for _ in 0..CEF_MESSAGE_LOOP_MAX_ITERATIONS {
 				self.cef_context.work();
 			}
+		} else if let Some(cef_schedule) = self.cef_schedule {
+			wait_until = wait_until.min(cef_schedule);
 		}
-		if let Some(window) = &self.window.as_ref() {
-			window.request_redraw();
-		}
-
 		event_loop.set_control_flow(ControlFlow::WaitUntil(wait_until));
 	}
 }

desktop/src/render/state.rs

@@ -23,6 +23,7 @@ pub(crate) struct RenderState {
 	bind_group: Option<wgpu::BindGroup>,
 	#[derivative(Debug = "ignore")]
 	overlays_scene: Option<vello::Scene>,
+	surface_outdated: bool,
 }
 
 impl RenderState {
@@ -186,6 +187,7 @@ impl RenderState {
 			ui_texture: None,
 			bind_group: None,
 			overlays_scene: None,
+			surface_outdated: true,
 		}
 	}
 
@@ -196,6 +198,7 @@ impl RenderState {
 
 		self.desired_width = width;
 		self.desired_height = height;
+		self.surface_outdated = true;
 
 		if width > 0 && height > 0 && (self.config.width != width || self.config.height != height) {
 			self.config.width = width;
@@ -215,14 +218,17 @@ impl RenderState {
 	}
 
 	pub(crate) fn set_viewport_scale(&mut self, scale: [f32; 2]) {
+		self.surface_outdated = true;
 		self.viewport_scale = scale;
 	}
 
 	pub(crate) fn set_viewport_offset(&mut self, offset: [f32; 2]) {
+		self.surface_outdated = true;
 		self.viewport_offset = offset;
 	}
 
 	pub(crate) fn set_overlays_scene(&mut self, scene: vello::Scene) {
+		self.surface_outdated = true;
 		self.overlays_scene = Some(scene);
 	}
 
@@ -241,6 +247,9 @@ impl RenderState {
 	}
 
 	pub(crate) fn render(&mut self, window: &Window) -> Result<(), RenderError> {
+		if !self.surface_outdated {
+			return Ok(());
+		}
 		let ui_scale = if let Some(ui_texture) = &self.ui_texture
 			&& (self.desired_width != ui_texture.width() || self.desired_height != ui_texture.height())
 		{
@@ -302,11 +311,13 @@ impl RenderState {
 		if ui_scale.is_some() {
 			return Err(RenderError::OutdatedUITextureError);
 		}
+		self.surface_outdated = false;
 
 		Ok(())
 	}
 
 	fn update_bindgroup(&mut self) {
+		self.surface_outdated = true;
 		let viewport_texture_view = self.viewport_texture.as_ref().unwrap_or(&self.transparent_texture).create_view(&wgpu::TextureViewDescriptor::default());
 		let overlays_texture_view = self
 			.overlays_texture