Fix 2D BatchedInstanceBuffer clear (#12922)

# Objective

- `cargo run --release --example bevymark -- --benchmark --waves 160
--per-wave 1000 --mode mesh2d` runs slower and slower over time due to
`no_gpu_preprocessing::write_batched_instance_buffer<bevy_sprite::mesh2d::mesh::Mesh2dPipeline>`
taking longer and longer because the `BatchedInstanceBuffer` is not
cleared

## Solution

- Split the `clear_batched_instance_buffers` system into CPU and GPU
versions
- Use the CPU version for 2D meshes

Author: superdump

crates/bevy_pbr/src/render/mesh.rs

@@ -15,8 +15,8 @@ use bevy_ecs::{
 use bevy_math::{Affine3, Rect, UVec2, Vec3, Vec4};
 use bevy_render::{
     batching::{
-        clear_batched_instance_buffers, gpu_preprocessing, no_gpu_preprocessing, GetBatchData,
-        GetFullBatchData, NoAutomaticBatching,
+        gpu_preprocessing, no_gpu_preprocessing, GetBatchData, GetFullBatchData,
+        NoAutomaticBatching,
     },
     mesh::*,
     render_asset::RenderAssets,
@@ -139,10 +139,14 @@ impl Plugin for MeshRenderPlugin {
                 .init_resource::<SkinIndices>()
                 .init_resource::<MorphUniform>()
                 .init_resource::<MorphIndices>()
-                .add_systems(ExtractSchedule, (extract_skins, extract_morphs))
                 .add_systems(
                     ExtractSchedule,
-                    clear_batched_instance_buffers::<MeshPipeline>.before(ExtractMeshesSet),
+                    (
+                        extract_skins,
+                        extract_morphs,
+                        gpu_preprocessing::clear_batched_gpu_instance_buffers::<MeshPipeline>
+                            .before(ExtractMeshesSet),
+                    ),
                 )
                 .add_systems(
                     Render,
@@ -151,6 +155,9 @@ impl Plugin for MeshRenderPlugin {
                         prepare_morphs.in_set(RenderSet::PrepareResources),
                         prepare_mesh_bind_group.in_set(RenderSet::PrepareBindGroups),
                         prepare_mesh_view_bind_groups.in_set(RenderSet::PrepareBindGroups),
+                        no_gpu_preprocessing::clear_batched_cpu_instance_buffers::<MeshPipeline>
+                            .in_set(RenderSet::Cleanup)
+                            .after(RenderSet::Render),
                     ),
                 );
         }

crates/bevy_render/src/batching/gpu_preprocessing.rs

@@ -125,10 +125,28 @@ where
     }
 }
 
+/// A system that runs early in extraction and clears out all the
+/// [`BatchedInstanceBuffers`] for the frame.
+///
+/// We have to run this during extraction because, if GPU preprocessing is in
+/// use, the extraction phase will write to the mesh input uniform buffers
+/// directly, so the buffers need to be cleared before then.
+pub fn clear_batched_gpu_instance_buffers<GFBD>(
+    gpu_batched_instance_buffers: Option<
+        ResMut<BatchedInstanceBuffers<GFBD::BufferData, GFBD::BufferInputData>>,
+    >,
+) where
+    GFBD: GetFullBatchData,
+{
+    if let Some(mut gpu_batched_instance_buffers) = gpu_batched_instance_buffers {
+        gpu_batched_instance_buffers.clear();
+    }
+}
+
 /// A system that removes GPU preprocessing work item buffers that correspond to
 /// deleted [`ViewTarget`]s.
 ///
-/// This is a separate system from [`super::clear_batched_instance_buffers`]
+/// This is a separate system from [`clear_batched_gpu_instance_buffers`]
 /// because [`ViewTarget`]s aren't created until after the extraction phase is
 /// completed.
 pub fn delete_old_work_item_buffers<GFBD>(

crates/bevy_render/src/batching/mod.rs

@@ -1,7 +1,7 @@
 use bevy_ecs::{
     component::Component,
     entity::Entity,
-    system::{Query, ResMut, SystemParam, SystemParamItem},
+    system::{Query, SystemParam, SystemParamItem},
 };
 use bytemuck::Pod;
 use nonmax::NonMaxU32;
@@ -135,30 +135,6 @@ pub trait GetFullBatchData: GetBatchData {
     ) -> Option<NonMaxU32>;
 }
 
-/// A system that runs early in extraction and clears out all the
-/// [`gpu_preprocessing::BatchedInstanceBuffers`] for the frame.
-///
-/// We have to run this during extraction because, if GPU preprocessing is in
-/// use, the extraction phase will write to the mesh input uniform buffers
-/// directly, so the buffers need to be cleared before then.
-pub fn clear_batched_instance_buffers<GFBD>(
-    cpu_batched_instance_buffer: Option<
-        ResMut<no_gpu_preprocessing::BatchedInstanceBuffer<GFBD::BufferData>>,
-    >,
-    gpu_batched_instance_buffers: Option<
-        ResMut<gpu_preprocessing::BatchedInstanceBuffers<GFBD::BufferData, GFBD::BufferInputData>>,
-    >,
-) where
-    GFBD: GetFullBatchData,
-{
-    if let Some(mut cpu_batched_instance_buffer) = cpu_batched_instance_buffer {
-        cpu_batched_instance_buffer.clear();
-    }
-    if let Some(mut gpu_batched_instance_buffers) = gpu_batched_instance_buffers {
-        gpu_batched_instance_buffers.clear();
-    }
-}
-
 /// Sorts a render phase that uses bins.
 pub fn sort_binned_render_phase<BPI>(mut views: Query<&mut BinnedRenderPhase<BPI>>)
 where

crates/bevy_render/src/batching/no_gpu_preprocessing.rs

@@ -43,6 +43,19 @@ where
     }
 }
 
+/// A system that clears out the [`BatchedInstanceBuffer`] for the frame.
+///
+/// This needs to run before the CPU batched instance buffers are used.
+pub fn clear_batched_cpu_instance_buffers<GBD>(
+    cpu_batched_instance_buffer: Option<ResMut<BatchedInstanceBuffer<GBD::BufferData>>>,
+) where
+    GBD: GetBatchData,
+{
+    if let Some(mut cpu_batched_instance_buffer) = cpu_batched_instance_buffer {
+        cpu_batched_instance_buffer.clear();
+    }
+}
+
 /// Batch the items in a sorted render phase, when GPU instance buffer building
 /// isn't in use. This means comparing metadata needed to draw each phase item
 /// and trying to combine the draws into a batch.

crates/bevy_sprite/src/mesh2d/mesh.rs

@@ -12,7 +12,8 @@ use bevy_ecs::{
 use bevy_math::{Affine3, Vec4};
 use bevy_reflect::{std_traits::ReflectDefault, Reflect};
 use bevy_render::batching::no_gpu_preprocessing::{
-    batch_and_prepare_sorted_render_phase, write_batched_instance_buffer, BatchedInstanceBuffer,
+    self, batch_and_prepare_sorted_render_phase, write_batched_instance_buffer,
+    BatchedInstanceBuffer,
 };
 use bevy_render::mesh::{GpuMesh, MeshVertexBufferLayoutRef};
 use bevy_render::{
@@ -107,6 +108,9 @@ impl Plugin for Mesh2dRenderPlugin {
                             .in_set(RenderSet::PrepareResourcesFlush),
                         prepare_mesh2d_bind_group.in_set(RenderSet::PrepareBindGroups),
                         prepare_mesh2d_view_bind_groups.in_set(RenderSet::PrepareBindGroups),
+                        no_gpu_preprocessing::clear_batched_cpu_instance_buffers::<Mesh2dPipeline>
+                            .in_set(RenderSet::Cleanup)
+                            .after(RenderSet::Render),
                     ),
                 );
         }