Multithreaded render command encoding (#9172)

# Objective
- Encoding many GPU commands (such as in a renderpass with many draws,
such as the main opaque pass) onto a `wgpu::CommandEncoder` is very
expensive, and takes a long time.
- To improve performance, we want to perform the command encoding for
these heavy passes in parallel.

## Solution
- `RenderContext` can now queue up "command buffer generation tasks"
which are closures that will generate a command buffer when called.
- When finalizing the render context to produce the final list of
command buffers, these tasks are run in parallel on the
`ComputeTaskPool` to produce their corresponding command buffers.
- The general idea is that the node graph will run in serial, but in a
node, instead of doing rendering work, you can add tasks to do render
work in parallel with other node's tasks that get ran at the end of the
graph execution.

## Nodes Parallelized
- `MainOpaquePass3dNode`
- `PrepassNode`
- `DeferredGBufferPrepassNode`
- `ShadowPassNode` (One task per view)


## Future Work
- For large number of draws calls, might be worth further subdividing
passes into 2+ tasks.
- Extend this to UI, 2d, transparent, and transmissive nodes?
- Needs testing - small command buffers are inefficient - it may be
worth reverting to the serial command encoder usage for render phases
with few items.
- All "serial" (traditional) rendering work must finish before parallel
rendering tasks (the new stuff) can start to run.
- There is still only one submission to the graphics queue at the end of
the graph execution. There is still no ability to submit work earlier.

## Performance Improvement
Thanks to @Elabajaba for testing on Bistro.


![image](https://github.com/bevyengine/bevy/assets/47158642/be50dafa-85eb-4da5-a5cd-c0a044f1e76f)


TLDR: Without shadow mapping, this PR has no impact. _With_ shadow
mapping, this PR gives **~40 more fps** than main.

---

## Changelog
- `MainOpaquePass3dNode`, `PrepassNode`, `DeferredGBufferPrepassNode`,
and each shadow map within `ShadowPassNode` are now encoded in parallel,
giving _greatly_ increased CPU performance, mainly when shadow mapping
is enabled.
  - Does not work on WASM or AMD+Windows+Vulkan.
- Added `RenderContext::add_command_buffer_generation_task()`.
- `RenderContext::new()` now takes adapter info
- Some render graph and Node related types and methods now have
additional lifetime constraints.


## Migration Guide
`RenderContext::new()` now takes adapter info
- Some render graph and Node related types and methods now have
additional lifetime constraints.

---------

Co-authored-by: Elabajaba <Elabajaba@users.noreply.github.com>
Co-authored-by: François <mockersf@gmail.com>

crates/bevy_core_pipeline/src/core_3d/main_opaque_pass_3d_node.rs

@@ -6,8 +6,8 @@ use bevy_ecs::{prelude::World, query::QueryItem};
 use bevy_render::{
     camera::ExtractedCamera,
     render_graph::{NodeRunError, RenderGraphContext, ViewNode},
-    render_phase::RenderPhase,
-    render_resource::{PipelineCache, RenderPassDescriptor, StoreOp},
+    render_phase::{RenderPhase, TrackedRenderPass},
+    render_resource::{CommandEncoderDescriptor, PipelineCache, RenderPassDescriptor, StoreOp},
     renderer::RenderContext,
     view::{ViewDepthTexture, ViewTarget, ViewUniformOffset},
 };
@@ -31,10 +31,10 @@ impl ViewNode for MainOpaquePass3dNode {
         &'static ViewUniformOffset,
     );
 
-    fn run(
+    fn run<'w>(
         &self,
         graph: &mut RenderGraphContext,
-        render_context: &mut RenderContext,
+        render_context: &mut RenderContext<'w>,
         (
             camera,
             opaque_phase,
@@ -44,52 +44,69 @@ impl ViewNode for MainOpaquePass3dNode {
             skybox_pipeline,
             skybox_bind_group,
             view_uniform_offset,
-        ): QueryItem<Self::ViewQuery>,
-        world: &World,
+        ): QueryItem<'w, Self::ViewQuery>,
+        world: &'w World,
     ) -> Result<(), NodeRunError> {
-        // Run the opaque pass, sorted by pipeline key and mesh id to greatly improve batching.
-        // NOTE: Scoped to drop the mutable borrow of render_context
-        #[cfg(feature = "trace")]
-        let _main_opaque_pass_3d_span = info_span!("main_opaque_pass_3d").entered();
+        let color_attachments = [Some(target.get_color_attachment())];
+        let depth_stencil_attachment = Some(depth.get_attachment(StoreOp::Store));
 
-        // Setup render pass
-        let mut render_pass = render_context.begin_tracked_render_pass(RenderPassDescriptor {
-            label: Some("main_opaque_pass_3d"),
-            color_attachments: &[Some(target.get_color_attachment())],
-            depth_stencil_attachment: Some(depth.get_attachment(StoreOp::Store)),
-            timestamp_writes: None,
-            occlusion_query_set: None,
-        });
+        let view_entity = graph.view_entity();
+        render_context.add_command_buffer_generation_task(move |render_device| {
+            #[cfg(feature = "trace")]
+            let _main_opaque_pass_3d_span = info_span!("main_opaque_pass_3d").entered();
 
-        if let Some(viewport) = camera.viewport.as_ref() {
-            render_pass.set_camera_viewport(viewport);
-        }
+            // Command encoder setup
+            let mut command_encoder =
+                render_device.create_command_encoder(&CommandEncoderDescriptor {
+                    label: Some("main_opaque_pass_3d_command_encoder"),
+                });
 
-        let view_entity = graph.view_entity();
+            // Render pass setup
+            let render_pass = command_encoder.begin_render_pass(&RenderPassDescriptor {
+                label: Some("main_opaque_pass_3d"),
+                color_attachments: &color_attachments,
+                depth_stencil_attachment,
+                timestamp_writes: None,
+                occlusion_query_set: None,
+            });
+            let mut render_pass = TrackedRenderPass::new(&render_device, render_pass);
+            if let Some(viewport) = camera.viewport.as_ref() {
+                render_pass.set_camera_viewport(viewport);
+            }
 
-        // Opaque draws
-        opaque_phase.render(&mut render_pass, world, view_entity);
+            // Opaque draws
+            if !opaque_phase.items.is_empty() {
+                #[cfg(feature = "trace")]
+                let _opaque_main_pass_3d_span = info_span!("opaque_main_pass_3d").entered();
+                opaque_phase.render(&mut render_pass, world, view_entity);
+            }
 
-        // Alpha draws
-        if !alpha_mask_phase.items.is_empty() {
-            alpha_mask_phase.render(&mut render_pass, world, view_entity);
-        }
+            // Alpha draws
+            if !alpha_mask_phase.items.is_empty() {
+                #[cfg(feature = "trace")]
+                let _alpha_mask_main_pass_3d_span = info_span!("alpha_mask_main_pass_3d").entered();
+                alpha_mask_phase.render(&mut render_pass, world, view_entity);
+            }
 
-        // Draw the skybox using a fullscreen triangle
-        if let (Some(skybox_pipeline), Some(SkyboxBindGroup(skybox_bind_group))) =
-            (skybox_pipeline, skybox_bind_group)
-        {
-            let pipeline_cache = world.resource::<PipelineCache>();
-            if let Some(pipeline) = pipeline_cache.get_render_pipeline(skybox_pipeline.0) {
-                render_pass.set_render_pipeline(pipeline);
-                render_pass.set_bind_group(
-                    0,
-                    &skybox_bind_group.0,
-                    &[view_uniform_offset.offset, skybox_bind_group.1],
-                );
-                render_pass.draw(0..3, 0..1);
+            // Skybox draw using a fullscreen triangle
+            if let (Some(skybox_pipeline), Some(SkyboxBindGroup(skybox_bind_group))) =
+                (skybox_pipeline, skybox_bind_group)
+            {
+                let pipeline_cache = world.resource::<PipelineCache>();
+                if let Some(pipeline) = pipeline_cache.get_render_pipeline(skybox_pipeline.0) {
+                    render_pass.set_render_pipeline(pipeline);
+                    render_pass.set_bind_group(
+                        0,
+                        &skybox_bind_group.0,
+                        &[view_uniform_offset.offset, skybox_bind_group.1],
+                    );
+                    render_pass.draw(0..3, 0..1);
+                }
             }
-        }
+
+            drop(render_pass);
+            command_encoder.finish()
+        });
 
         Ok(())
     }

crates/bevy_core_pipeline/src/deferred/node.rs

@@ -2,7 +2,8 @@ use bevy_ecs::prelude::*;
 use bevy_ecs::query::QueryItem;
 use bevy_render::render_graph::ViewNode;
 
-use bevy_render::render_resource::StoreOp;
+use bevy_render::render_phase::TrackedRenderPass;
+use bevy_render::render_resource::{CommandEncoderDescriptor, StoreOp};
 use bevy_render::{
     camera::ExtractedCamera,
     render_graph::{NodeRunError, RenderGraphContext},
@@ -33,21 +34,19 @@ impl ViewNode for DeferredGBufferPrepassNode {
         &'static ViewPrepassTextures,
     );
 
-    fn run(
+    fn run<'w>(
         &self,
         graph: &mut RenderGraphContext,
-        render_context: &mut RenderContext,
+        render_context: &mut RenderContext<'w>,
         (
             camera,
             opaque_deferred_phase,
             alpha_mask_deferred_phase,
             view_depth_texture,
             view_prepass_textures,
-        ): QueryItem<Self::ViewQuery>,
-        world: &World,
+        ): QueryItem<'w, Self::ViewQuery>,
+        world: &'w World,
     ) -> Result<(), NodeRunError> {
-        let view_entity = graph.view_entity();
-
         let mut color_attachments = vec![];
         color_attachments.push(
             view_prepass_textures
@@ -107,49 +106,64 @@ impl ViewNode for DeferredGBufferPrepassNode {
                 .map(|deferred_lighting_pass_id| deferred_lighting_pass_id.get_attachment()),
         );
 
+        // If all color attachments are none: clear the color attachment list so that no fragment shader is required
         if color_attachments.iter().all(Option::is_none) {
-            // All attachments are none: clear the attachment list so that no fragment shader is required.
             color_attachments.clear();
         }
 
-        {
-            // Set up the pass descriptor with the depth attachment and optional color attachments.
-            let mut render_pass = render_context.begin_tracked_render_pass(RenderPassDescriptor {
+        let depth_stencil_attachment = Some(view_depth_texture.get_attachment(StoreOp::Store));
+
+        let view_entity = graph.view_entity();
+        render_context.add_command_buffer_generation_task(move |render_device| {
+            #[cfg(feature = "trace")]
+            let _deferred_span = info_span!("deferred").entered();
+
+            // Command encoder setup
+            let mut command_encoder =
+                render_device.create_command_encoder(&CommandEncoderDescriptor {
+                    label: Some("deferred_command_encoder"),
+                });
+
+            // Render pass setup
+            let render_pass = command_encoder.begin_render_pass(&RenderPassDescriptor {
                 label: Some("deferred"),
                 color_attachments: &color_attachments,
-                depth_stencil_attachment: Some(view_depth_texture.get_attachment(StoreOp::Store)),
+                depth_stencil_attachment,
                 timestamp_writes: None,
                 occlusion_query_set: None,
             });
-
+            let mut render_pass = TrackedRenderPass::new(&render_device, render_pass);
             if let Some(viewport) = camera.viewport.as_ref() {
                 render_pass.set_camera_viewport(viewport);
             }
 
-            // Always run deferred pass to ensure the deferred gbuffer and deferred_lighting_pass_id are cleared.
-            {
-                // Run the prepass, sorted front-to-back.
+            // Opaque draws
+            if !opaque_deferred_phase.items.is_empty() {
                 #[cfg(feature = "trace")]
                 let _opaque_prepass_span = info_span!("opaque_deferred").entered();
                 opaque_deferred_phase.render(&mut render_pass, world, view_entity);
             }
 
+            // Alpha masked draws
             if !alpha_mask_deferred_phase.items.is_empty() {
-                // Run the deferred, sorted front-to-back.
                 #[cfg(feature = "trace")]
                 let _alpha_mask_deferred_span = info_span!("alpha_mask_deferred").entered();
                 alpha_mask_deferred_phase.render(&mut render_pass, world, view_entity);
             }
-        }
 
-        if let Some(prepass_depth_texture) = &view_prepass_textures.depth {
-            // Copy depth buffer to texture.
-            render_context.command_encoder().copy_texture_to_texture(
-                view_depth_texture.texture.as_image_copy(),
-                prepass_depth_texture.texture.texture.as_image_copy(),
-                view_prepass_textures.size,
-            );
-        }
+            drop(render_pass);
+
+            // Copy prepass depth to the main depth texture
+            if let Some(prepass_depth_texture) = &view_prepass_textures.depth {
+                command_encoder.copy_texture_to_texture(
+                    view_depth_texture.texture.as_image_copy(),
+                    prepass_depth_texture.texture.texture.as_image_copy(),
+                    view_prepass_textures.size,
+                );
+            }
+
+            command_encoder.finish()
+        });
 
         Ok(())
     }

crates/bevy_core_pipeline/src/prepass/node.rs

@@ -1,12 +1,10 @@
 use bevy_ecs::prelude::*;
 use bevy_ecs::query::QueryItem;
-use bevy_render::render_graph::ViewNode;
-use bevy_render::render_resource::StoreOp;
 use bevy_render::{
     camera::ExtractedCamera,
-    render_graph::{NodeRunError, RenderGraphContext},
-    render_phase::RenderPhase,
-    render_resource::RenderPassDescriptor,
+    render_graph::{NodeRunError, RenderGraphContext, ViewNode},
+    render_phase::{RenderPhase, TrackedRenderPass},
+    render_resource::{CommandEncoderDescriptor, RenderPassDescriptor, StoreOp},
     renderer::RenderContext,
     view::ViewDepthTexture,
 };
@@ -31,22 +29,20 @@ impl ViewNode for PrepassNode {
         Option<&'static DeferredPrepass>,
     );
 
-    fn run(
+    fn run<'w>(
         &self,
         graph: &mut RenderGraphContext,
-        render_context: &mut RenderContext,
+        render_context: &mut RenderContext<'w>,
         (
             camera,
             opaque_prepass_phase,
             alpha_mask_prepass_phase,
             view_depth_texture,
             view_prepass_textures,
             deferred_prepass,
-        ): QueryItem<Self::ViewQuery>,
-        world: &World,
+        ): QueryItem<'w, Self::ViewQuery>,
+        world: &'w World,
     ) -> Result<(), NodeRunError> {
-        let view_entity = graph.view_entity();
-
         let mut color_attachments = vec![
             view_prepass_textures
                 .normal
@@ -56,55 +52,72 @@ impl ViewNode for PrepassNode {
                 .motion_vectors
                 .as_ref()
                 .map(|motion_vectors_texture| motion_vectors_texture.get_attachment()),
-            // Use None in place of Deferred attachments
+            // Use None in place of deferred attachments
             None,
             None,
         ];
 
+        // If all color attachments are none: clear the color attachment list so that no fragment shader is required
         if color_attachments.iter().all(Option::is_none) {
-            // all attachments are none: clear the attachment list so that no fragment shader is required
             color_attachments.clear();
         }
 
-        {
-            // Set up the pass descriptor with the depth attachment and optional color attachments
-            let mut render_pass = render_context.begin_tracked_render_pass(RenderPassDescriptor {
+        let depth_stencil_attachment = Some(view_depth_texture.get_attachment(StoreOp::Store));
+
+        let view_entity = graph.view_entity();
+        render_context.add_command_buffer_generation_task(move |render_device| {
+            #[cfg(feature = "trace")]
+            let _prepass_span = info_span!("prepass").entered();
+
+            // Command encoder setup
+            let mut command_encoder =
+                render_device.create_command_encoder(&CommandEncoderDescriptor {
+                    label: Some("prepass_command_encoder"),
+                });
+
+            // Render pass setup
+            let render_pass = command_encoder.begin_render_pass(&RenderPassDescriptor {
                 label: Some("prepass"),
                 color_attachments: &color_attachments,
-                depth_stencil_attachment: Some(view_depth_texture.get_attachment(StoreOp::Store)),
+                depth_stencil_attachment,
                 timestamp_writes: None,
                 occlusion_query_set: None,
             });
+            let mut render_pass = TrackedRenderPass::new(&render_device, render_pass);
             if let Some(viewport) = camera.viewport.as_ref() {
                 render_pass.set_camera_viewport(viewport);
             }
 
-            // Always run opaque pass to ensure screen is cleared
-            {
-                // Run the prepass, sorted front-to-back
+            // Opaque draws
+            if !opaque_prepass_phase.items.is_empty() {
                 #[cfg(feature = "trace")]
                 let _opaque_prepass_span = info_span!("opaque_prepass").entered();
                 opaque_prepass_phase.render(&mut render_pass, world, view_entity);
             }
 
+            // Alpha masked draws
             if !alpha_mask_prepass_phase.items.is_empty() {
-                // Run the prepass, sorted front-to-back
                 #[cfg(feature = "trace")]
                 let _alpha_mask_prepass_span = info_span!("alpha_mask_prepass").entered();
                 alpha_mask_prepass_phase.render(&mut render_pass, world, view_entity);
             }
-        }
-        if deferred_prepass.is_none() {
-            // Copy if deferred isn't going to
-            if let Some(prepass_depth_texture) = &view_prepass_textures.depth {
-                // Copy depth buffer to texture
-                render_context.command_encoder().copy_texture_to_texture(
-                    view_depth_texture.texture.as_image_copy(),
-                    prepass_depth_texture.texture.texture.as_image_copy(),
-                    view_prepass_textures.size,
-                );
+
+            drop(render_pass);
+
+            // Copy prepass depth to the main depth texture if deferred isn't going to
+            if deferred_prepass.is_none() {
+                if let Some(prepass_depth_texture) = &view_prepass_textures.depth {
+                    command_encoder.copy_texture_to_texture(
+                        view_depth_texture.texture.as_image_copy(),
+                        prepass_depth_texture.texture.texture.as_image_copy(),
+                        view_prepass_textures.size,
+                    );
+                }
             }
-        }
+
+            command_encoder.finish()
+        });
+
         Ok(())
     }
 }