Wgpu render pass on paint callback has now static lifetime

crates/eframe/src/web/web_painter_wgpu.rs

@@ -302,7 +302,7 @@ impl WebPainter for WebPainterWgpu {
                 let frame_view = frame
                     .texture
                     .create_view(&wgpu::TextureViewDescriptor::default());
-                let mut render_pass = encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
+                let render_pass = encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
                     color_attachments: &[Some(wgpu::RenderPassColorAttachment {
                         view: &frame_view,
                         resolve_target: None,
@@ -333,7 +333,14 @@ impl WebPainter for WebPainterWgpu {
                     timestamp_writes: None,
                 });
 
-                renderer.render(&mut render_pass, clipped_primitives, &screen_descriptor);
+                // Forgetting the pass' lifetime means that we are no longer compile-time protected from
+                // runtime errors caused by accessing the parent encoder before the render pass is dropped.
+                // Since we don't pass it on to the renderer, we should be perfectly safe against this mistake here!
+                renderer.render(
+                    &mut render_pass.forget_lifetime(),
+                    clipped_primitives,
+                    &screen_descriptor,
+                );
             }
 
             Some(frame)

crates/egui-wgpu/src/renderer.rs

@@ -112,11 +112,11 @@ pub trait CallbackTrait: Send + Sync {
     ///
     /// It is given access to the [`wgpu::RenderPass`] so that it can issue draw commands
     /// into the same [`wgpu::RenderPass`] that is used for all other egui elements.
-    fn paint<'a>(
-        &'a self,
+    fn paint(
+        &self,
         info: PaintCallbackInfo,
-        render_pass: &mut wgpu::RenderPass<'a>,
-        callback_resources: &'a CallbackResources,
+        render_pass: &mut wgpu::RenderPass<'static>,
+        callback_resources: &CallbackResources,
     );
 }
 
@@ -408,10 +408,16 @@ impl Renderer {
     }
 
     /// Executes the egui renderer onto an existing wgpu renderpass.
-    pub fn render<'rp>(
-        &'rp self,
-        render_pass: &mut wgpu::RenderPass<'rp>,
-        paint_jobs: &'rp [epaint::ClippedPrimitive],
+    ///
+    /// Note that the lifetime of `render_pass` is `'static` which requires a call to [`wgpu::RenderPass::forget_lifetime`].
+    /// This allows users to pass resources that live outside of the callback resources to the render pass.
+    /// The render pass internally keeps all referenced resources alive as long as necessary.
+    /// The only consequence of `forget_lifetime` is that any operation on the parent encoder will cause a runtime error
+    /// instead of a compile time error.
+    pub fn render(
+        &self,
+        render_pass: &mut wgpu::RenderPass<'static>,
+        paint_jobs: &[epaint::ClippedPrimitive],
         screen_descriptor: &ScreenDescriptor,
     ) {
         crate::profile_function!();

crates/egui-wgpu/src/winit.rs

@@ -627,7 +627,7 @@ impl Painter {
                     (texture_view, Some(&frame_view))
                 });
 
-            let mut render_pass = encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
+            let render_pass = encoder.begin_render_pass(&wgpu::RenderPassDescriptor {
                 label: Some("egui_render"),
                 color_attachments: &[Some(wgpu::RenderPassColorAttachment {
                     view,
@@ -658,7 +658,14 @@ impl Painter {
                 occlusion_query_set: None,
             });
 
-            renderer.render(&mut render_pass, clipped_primitives, &screen_descriptor);
+            // Forgetting the pass' lifetime means that we are no longer compile-time protected from
+            // runtime errors caused by accessing the parent encoder before the render pass is dropped.
+            // Since we don't pass it on to the renderer, we should be perfectly safe against this mistake here!
+            renderer.render(
+                &mut render_pass.forget_lifetime(),
+                clipped_primitives,
+                &screen_descriptor,
+            );
         }
 
         {

crates/egui_demo_app/src/apps/custom3d_wgpu.rs

@@ -160,11 +160,11 @@ impl egui_wgpu::CallbackTrait for CustomTriangleCallback {
         Vec::new()
     }
 
-    fn paint<'a>(
+    fn paint(
         &self,
         _info: egui::PaintCallbackInfo,
-        render_pass: &mut wgpu::RenderPass<'a>,
-        resources: &'a egui_wgpu::CallbackResources,
+        render_pass: &mut wgpu::RenderPass<'static>,
+        resources: &egui_wgpu::CallbackResources,
     ) {
         let resources: &TriangleRenderResources = resources.get().unwrap();
         resources.paint(render_pass);
@@ -200,7 +200,7 @@ impl TriangleRenderResources {
         );
     }
 
-    fn paint<'rp>(&'rp self, render_pass: &mut wgpu::RenderPass<'rp>) {
+    fn paint(&self, render_pass: &mut wgpu::RenderPass<'_>) {
         // Draw our triangle!
         render_pass.set_pipeline(&self.pipeline);
         render_pass.set_bind_group(0, &self.bind_group, &[]);