wgpu: Keep a CommandEncoder for the duration of a frame, extract out a struct to hold it with a StagingBelt

render/wgpu/src/backend.rs

@@ -45,7 +45,6 @@ const TEXTURE_READS_BEFORE_PROMOTION: u8 = 5;
 
 pub struct WgpuRenderBackend<T: RenderTarget> {
     pub(crate) descriptors: Arc<Descriptors>,
-    staging_belt: wgpu::util::StagingBelt,
     target: T,
     surface: Surface,
     meshes: Vec<Mesh>,
@@ -57,6 +56,7 @@ pub struct WgpuRenderBackend<T: RenderTarget> {
     offscreen_texture_pool: TexturePool,
     pub(crate) offscreen_buffer_pool: Arc<BufferPool<wgpu::Buffer, BufferDimensions>>,
     dynamic_transforms: DynamicTransforms,
+    active_frame: ActiveFrame,
 }
 
 impl WgpuRenderBackend<SwapChainTarget> {
@@ -219,10 +219,10 @@ impl<T: RenderTarget> WgpuRenderBackend<T> {
         ));
 
         let transforms = DynamicTransforms::new(&descriptors);
+        let active_frame = ActiveFrame::new(&descriptors);
 
         Ok(Self {
             descriptors,
-            staging_belt: wgpu::util::StagingBelt::new(65536),
             target,
             surface,
             meshes: Vec::new(),
@@ -232,6 +232,7 @@ impl<T: RenderTarget> WgpuRenderBackend<T> {
             offscreen_texture_pool: TexturePool::new(),
             offscreen_buffer_pool: Arc::new(offscreen_buffer_pool),
             dynamic_transforms: transforms,
+            active_frame,
         })
     }
 
@@ -534,14 +535,6 @@ impl<T: RenderTarget + 'static> RenderBackend for WgpuRenderBackend<T> {
             }
         };
 
-        let label = create_debug_label!("Draw encoder");
-        let mut draw_encoder =
-            self.descriptors
-                .device
-                .create_command_encoder(&wgpu::CommandEncoderDescriptor {
-                    label: label.as_deref(),
-                });
-
         for entry in cache_entries {
             let texture = as_texture(&entry.handle);
             let mut surface = Surface::new(
@@ -565,9 +558,9 @@ impl<T: RenderTarget + 'static> RenderBackend for WgpuRenderBackend<T> {
                     &self.descriptors,
                     &self.meshes,
                     entry.commands,
-                    &mut self.staging_belt,
+                    &mut self.active_frame.staging_belt,
                     &self.dynamic_transforms,
-                    &mut draw_encoder,
+                    &mut self.active_frame.command_encoder,
                     LayerRef::None,
                     &mut self.offscreen_texture_pool,
                 );
@@ -589,18 +582,18 @@ impl<T: RenderTarget + 'static> RenderBackend for WgpuRenderBackend<T> {
                     &self.descriptors,
                     &self.meshes,
                     entry.commands,
-                    &mut self.staging_belt,
+                    &mut self.active_frame.staging_belt,
                     &self.dynamic_transforms,
-                    &mut draw_encoder,
+                    &mut self.active_frame.command_encoder,
                     LayerRef::None,
                     &mut self.offscreen_texture_pool,
                 );
                 for filter in entry.filters {
                     target = self.descriptors.filters.apply(
                         &self.descriptors,
-                        &mut draw_encoder,
+                        &mut self.active_frame.command_encoder,
                         &mut self.offscreen_texture_pool,
-                        &mut self.staging_belt,
+                        &mut self.active_frame.staging_belt,
                         FilterSource::for_entire_texture(target.color_texture()),
                         filter,
                     );
@@ -614,7 +607,7 @@ impl<T: RenderTarget + 'static> RenderBackend for WgpuRenderBackend<T> {
                     target.whole_frame_bind_group(&self.descriptors),
                     target.globals(),
                     target.color_texture().sample_count(),
-                    &mut draw_encoder,
+                    &mut self.active_frame.command_encoder,
                 );
             }
         }
@@ -628,23 +621,18 @@ impl<T: RenderTarget + 'static> RenderBackend for WgpuRenderBackend<T> {
                 a: f64::from(clear.a) / 255.0,
             }),
             &self.descriptors,
-            &mut self.staging_belt,
+            &mut self.active_frame.staging_belt,
             &self.dynamic_transforms,
-            &mut draw_encoder,
+            &mut self.active_frame.command_encoder,
             &self.meshes,
             commands,
             LayerRef::None,
             &mut self.texture_pool,
         );
-        self.staging_belt.finish();
+        self.active_frame.staging_belt.finish();
 
-        self.target.submit(
-            &self.descriptors.device,
-            &self.descriptors.queue,
-            Some(draw_encoder.finish()),
-            frame_output,
-        );
-        self.staging_belt.recall();
+        self.active_frame
+            .submit(&self.descriptors, &self.target, frame_output);
         self.offscreen_texture_pool = TexturePool::new();
     }
 
@@ -786,33 +774,22 @@ impl<T: RenderTarget + 'static> RenderBackend for WgpuRenderBackend<T> {
             texture.texture.height(),
             wgpu::TextureFormat::Rgba8Unorm,
         );
-        let label = create_debug_label!("Draw encoder");
-        let mut draw_encoder =
-            self.descriptors
-                .device
-                .create_command_encoder(&wgpu::CommandEncoderDescriptor {
-                    label: label.as_deref(),
-                });
         surface.draw_commands_and_copy_to(
             frame_output.view(),
             RenderTargetMode::FreshWithTexture(target.get_texture()),
             &self.descriptors,
-            &mut self.staging_belt,
+            &mut self.active_frame.staging_belt,
             &self.dynamic_transforms,
-            &mut draw_encoder,
+            &mut self.active_frame.command_encoder,
             &self.meshes,
             commands,
             LayerRef::Current,
             &mut self.offscreen_texture_pool,
         );
-        self.staging_belt.finish();
-        let index = target.submit(
-            &self.descriptors.device,
-            &self.descriptors.queue,
-            Some(draw_encoder.finish()),
-            frame_output,
-        );
-        self.staging_belt.recall();
+
+        let index = self
+            .active_frame
+            .submit(&self.descriptors, &target, frame_output);
 
         Some(self.make_queue_sync_handle(target, Some(index), handle, bounds))
     }
@@ -878,7 +855,7 @@ impl<T: RenderTarget + 'static> RenderBackend for WgpuRenderBackend<T> {
             &self.descriptors,
             &mut draw_encoder,
             &mut self.offscreen_texture_pool,
-            &mut self.staging_belt,
+            &mut self.active_frame.staging_belt,
             FilterSource {
                 texture: &source_texture.texture,
                 point: source_point,
@@ -909,14 +886,14 @@ impl<T: RenderTarget + 'static> RenderBackend for WgpuRenderBackend<T> {
                 depth_or_array_layers: 1,
             },
         );
-        self.staging_belt.finish();
+        self.active_frame.staging_belt.finish();
         let index = target.submit(
             &self.descriptors.device,
             &self.descriptors.queue,
             Some(draw_encoder.finish()),
             frame_output,
         );
-        self.staging_belt.recall();
+        self.active_frame.staging_belt.recall();
 
         Some(self.make_queue_sync_handle(target, Some(index), destination, copy_area))
     }
@@ -1240,3 +1217,42 @@ impl RenderTargetMode {
         }
     }
 }
+
+pub struct ActiveFrame {
+    staging_belt: wgpu::util::StagingBelt,
+    command_encoder: wgpu::CommandEncoder,
+}
+
+impl ActiveFrame {
+    pub fn new(descriptors: &Descriptors) -> Self {
+        Self {
+            command_encoder: descriptors
+                .device
+                .create_command_encoder(&Default::default()),
+            staging_belt: wgpu::util::StagingBelt::new(65536),
+        }
+    }
+
+    pub fn submit<T: RenderTarget>(
+        &mut self,
+        descriptors: &Descriptors,
+        target: &T,
+        frame: T::Frame,
+    ) -> SubmissionIndex {
+        self.staging_belt.finish();
+        let draw_encoder = std::mem::replace(
+            &mut self.command_encoder,
+            descriptors
+                .device
+                .create_command_encoder(&Default::default()),
+        );
+        let index = target.submit(
+            &descriptors.device,
+            &descriptors.queue,
+            Some(draw_encoder.finish()),
+            frame,
+        );
+        self.staging_belt.recall();
+        index
+    }
+}