From 262f471934c99d77e8767275d95a7b4dbaf6a7c7 Mon Sep 17 00:00:00 2001
From: robtfm <50659922+robtfm@users.noreply.github.com>
Date: Mon, 4 Nov 2024 15:29:11 +0000
Subject: [PATCH] move mesh uniform construction out of Core3d (#16188)

# Objective

gpu based mesh uniform construction in the `GpuPreprocessNode` is
currently in `Core3d`. The node iterates all views and schedules the
uniform construction for each. so
- when there are multiple 3d cameras, it runs multiple times on each
view
- if a view wants to render meshes but doesn't use the `Core3d` graph,
the camera must run later than at least one `Core3d`-based camera (or
add the node to its own graph, duplicating the work)
- If views want to share mesh uniforms there is no way to avoid running
the preprocessing for every view

## Solution

- move the node to the top level of the rendergraph, before the camera
driver node
- make the `PreprocessBindGroup` `clone`able, and add a
`SkipGpuPreprocessing` component to allow opting out per view
---
 crates/bevy_pbr/src/render/gpu_preprocess.rs | 38 ++++++++++++--------
 1 file changed, 24 insertions(+), 14 deletions(-)

diff --git a/crates/bevy_pbr/src/render/gpu_preprocess.rs b/crates/bevy_pbr/src/render/gpu_preprocess.rs
index 3db9508c17..ee28005a8c 100644
--- a/crates/bevy_pbr/src/render/gpu_preprocess.rs
+++ b/crates/bevy_pbr/src/render/gpu_preprocess.rs
@@ -10,11 +10,10 @@ use core::num::NonZero;
 
 use bevy_app::{App, Plugin};
 use bevy_asset::{load_internal_asset, Handle};
-use bevy_core_pipeline::core_3d::graph::{Core3d, Node3d};
 use bevy_ecs::{
     component::Component,
     entity::Entity,
-    query::{Has, QueryState},
+    query::{Has, QueryState, Without},
     schedule::{common_conditions::resource_exists, IntoSystemConfigs as _},
     system::{lifetimeless::Read, Commands, Res, ResMut, Resource},
     world::{FromWorld, World},
@@ -24,7 +23,8 @@ use bevy_render::{
         BatchedInstanceBuffers, GpuPreprocessingSupport, IndirectParameters,
         IndirectParametersBuffer, PreprocessWorkItem,
     },
-    render_graph::{Node, NodeRunError, RenderGraphApp, RenderGraphContext},
+    graph::CameraDriverLabel,
+    render_graph::{Node, NodeRunError, RenderGraph, RenderGraphContext},
     render_resource::{
         binding_types::{storage_buffer, storage_buffer_read_only, uniform_buffer},
         BindGroup, BindGroupEntries, BindGroupLayout, BindingResource, BufferBinding,
@@ -65,12 +65,15 @@ pub struct GpuMeshPreprocessPlugin {
 
 /// The render node for the mesh uniform building pass.
 pub struct GpuPreprocessNode {
-    view_query: QueryState<(
-        Entity,
-        Read<PreprocessBindGroup>,
-        Read<ViewUniformOffset>,
-        Has<GpuCulling>,
-    )>,
+    view_query: QueryState<
+        (
+            Entity,
+            Read<PreprocessBindGroup>,
+            Read<ViewUniformOffset>,
+            Has<GpuCulling>,
+        ),
+        Without<SkipGpuPreprocess>,
+    >,
 }
 
 /// The compute shader pipelines for the mesh uniform building pass.
@@ -108,9 +111,14 @@ bitflags! {
 /// The compute shader bind group for the mesh uniform building pass.
 ///
 /// This goes on the view.
-#[derive(Component)]
+#[derive(Component, Clone)]
 pub struct PreprocessBindGroup(BindGroup);
 
+/// Stops the `GpuPreprocessNode` attempting to generate the buffer for this view
+/// useful to avoid duplicating effort if the bind group is shared between views
+#[derive(Component)]
+pub struct SkipGpuPreprocess;
+
 impl Plugin for GpuMeshPreprocessPlugin {
     fn build(&self, app: &mut App) {
         load_internal_asset!(
@@ -136,10 +144,12 @@ impl Plugin for GpuMeshPreprocessPlugin {
         }
 
         // Stitch the node in.
+        let gpu_preprocess_node = GpuPreprocessNode::from_world(render_app.world_mut());
+        let mut render_graph = render_app.world_mut().resource_mut::<RenderGraph>();
+        render_graph.add_node(NodePbr::GpuPreprocess, gpu_preprocess_node);
+        render_graph.add_node_edge(NodePbr::GpuPreprocess, CameraDriverLabel);
+
         render_app
-            .add_render_graph_node::<GpuPreprocessNode>(Core3d, NodePbr::GpuPreprocess)
-            .add_render_graph_edges(Core3d, (NodePbr::GpuPreprocess, Node3d::Prepass))
-            .add_render_graph_edges(Core3d, (NodePbr::GpuPreprocess, NodePbr::ShadowPass))
             .init_resource::<PreprocessPipelines>()
             .init_resource::<SpecializedComputePipelines<PreprocessPipeline>>()
             .add_systems(
@@ -200,7 +210,7 @@ impl Node for GpuPreprocessNode {
             // Grab the index buffer for this view.
             let Some(index_buffer) = index_buffers.get(&view) else {
                 warn!("The preprocessing index buffer wasn't present");
-                return Ok(());
+                continue;
             };
 
             // Select the right pipeline, depending on whether GPU culling is in