Stop extracting mesh entities to the render world. (#11803)

This fixes a `FIXME` in `extract_meshes` and results in a performance
improvement.

As a result of this change, meshes in the render world might not be
attached to entities anymore. Therefore, the `entity` parameter to
`RenderCommand::render()` is now wrapped in an `Option`. Most
applications that use the render app's ECS can simply unwrap the
`Option`.

Note that for now sprites, gizmos, and UI elements still use the render
world as usual.

## Migration guide

* For efficiency reasons, some meshes in the render world may not have
corresponding `Entity` IDs anymore. As a result, the `entity` parameter
to `RenderCommand::render()` is now wrapped in an `Option`. Custom
rendering code may need to be updated to handle the case in which no
`Entity` exists for an object that is to be rendered.

crates/bevy_gizmos/src/lib.rs

@@ -383,10 +383,13 @@ impl<const I: usize, P: PhaseItem> RenderCommand<P> for SetLineGizmoBindGroup<I>
     fn render<'w>(
         _item: &P,
         _view: ROQueryItem<'w, Self::ViewQuery>,
-        uniform_index: ROQueryItem<'w, Self::ItemQuery>,
+        uniform_index: Option<ROQueryItem<'w, Self::ItemQuery>>,
         bind_group: SystemParamItem<'w, '_, Self::Param>,
         pass: &mut TrackedRenderPass<'w>,
     ) -> RenderCommandResult {
+        let Some(uniform_index) = uniform_index else {
+            return RenderCommandResult::Failure;
+        };
         pass.set_bind_group(
             I,
             &bind_group.into_inner().bindgroup,
@@ -406,10 +409,13 @@ impl<P: PhaseItem> RenderCommand<P> for DrawLineGizmo {
     fn render<'w>(
         _item: &P,
         _view: ROQueryItem<'w, Self::ViewQuery>,
-        handle: ROQueryItem<'w, Self::ItemQuery>,
+        handle: Option<ROQueryItem<'w, Self::ItemQuery>>,
         line_gizmos: SystemParamItem<'w, '_, Self::Param>,
         pass: &mut TrackedRenderPass<'w>,
     ) -> RenderCommandResult {
+        let Some(handle) = handle else {
+            return RenderCommandResult::Failure;
+        };
         let Some(line_gizmo) = line_gizmos.into_inner().get(handle) else {
             return RenderCommandResult::Failure;
         };

crates/bevy_pbr/src/material.rs

@@ -388,7 +388,7 @@ impl<P: PhaseItem, M: Material, const I: usize> RenderCommand<P> for SetMaterial
     fn render<'w>(
         item: &P,
         _view: (),
-        _item_query: (),
+        _item_query: Option<()>,
         (materials, material_instances): SystemParamItem<'w, '_, Self::Param>,
         pass: &mut TrackedRenderPass<'w>,
     ) -> RenderCommandResult {

crates/bevy_pbr/src/prepass/mod.rs

@@ -912,7 +912,7 @@ impl<P: PhaseItem, const I: usize> RenderCommand<P> for SetPrepassViewBindGroup<
             &'_ ViewUniformOffset,
             Option<&'_ PreviousViewProjectionUniformOffset>,
         ),
-        _entity: (),
+        _entity: Option<()>,
         prepass_view_bind_group: SystemParamItem<'w, '_, Self::Param>,
         pass: &mut TrackedRenderPass<'w>,
     ) -> RenderCommandResult {

crates/bevy_pbr/src/render/mesh.rs

@@ -256,12 +256,7 @@ pub struct RenderMeshInstance {
 #[derive(Default, Resource, Deref, DerefMut)]
 pub struct RenderMeshInstances(EntityHashMap<Entity, RenderMeshInstance>);
 
-#[derive(Component)]
-pub struct Mesh3d;
-
 pub fn extract_meshes(
-    mut commands: Commands,
-    mut previous_len: Local<usize>,
     mut render_mesh_instances: ResMut<RenderMeshInstances>,
     mut thread_local_queues: Local<ThreadLocal<Cell<Vec<(Entity, RenderMeshInstance)>>>>,
     meshes_query: Extract<
@@ -328,15 +323,9 @@ pub fn extract_meshes(
     );
 
     render_mesh_instances.clear();
-    let mut entities = Vec::with_capacity(*previous_len);
     for queue in thread_local_queues.iter_mut() {
-        // FIXME: Remove this - it is just a workaround to enable rendering to work as
-        // render commands require an entity to exist at the moment.
-        entities.extend(queue.get_mut().iter().map(|(e, _)| (*e, Mesh3d)));
         render_mesh_instances.extend(queue.get_mut().drain(..));
     }
-    *previous_len = entities.len();
-    commands.insert_or_spawn_batch(entities);
 }
 
 #[derive(Resource, Clone)]
@@ -1050,7 +1039,7 @@ impl<P: PhaseItem, const I: usize> RenderCommand<P> for SetMeshViewBindGroup<I>
             'w,
             Self::ViewQuery,
         >,
-        _entity: (),
+        _entity: Option<()>,
         _: SystemParamItem<'w, '_, Self::Param>,
         pass: &mut TrackedRenderPass<'w>,
     ) -> RenderCommandResult {
@@ -1085,7 +1074,7 @@ impl<P: PhaseItem, const I: usize> RenderCommand<P> for SetMeshBindGroup<I> {
     fn render<'w>(
         item: &P,
         _view: (),
-        _item_query: (),
+        _item_query: Option<()>,
         (bind_groups, mesh_instances, skin_indices, morph_indices, lightmaps): SystemParamItem<
             'w,
             '_,
@@ -1154,7 +1143,7 @@ impl<P: PhaseItem> RenderCommand<P> for DrawMesh {
     fn render<'w>(
         item: &P,
         _view: (),
-        _item_query: (),
+        _item_query: Option<()>,
         (meshes, mesh_instances): SystemParamItem<'w, '_, Self::Param>,
         pass: &mut TrackedRenderPass<'w>,
     ) -> RenderCommandResult {

crates/bevy_render/src/render_phase/draw.rs

@@ -190,6 +190,11 @@ pub trait RenderCommand<P: PhaseItem> {
     ///
     /// The item is the entity that will be rendered for the corresponding view.
     /// All components have to be accessed read only.
+    ///
+    /// For efficiency reasons, Bevy doesn't always extract entities to the
+    /// render world; for instance, entities that simply consist of meshes are
+    /// often not extracted. If the entity doesn't exist in the render world,
+    /// the supplied query data will be `None`.
     type ItemQuery: ReadOnlyQueryData;
 
     /// Renders a [`PhaseItem`] by recording commands (e.g. setting pipelines, binding bind groups,
@@ -197,7 +202,7 @@ pub trait RenderCommand<P: PhaseItem> {
     fn render<'w>(
         item: &P,
         view: ROQueryItem<'w, Self::ViewQuery>,
-        entity: ROQueryItem<'w, Self::ItemQuery>,
+        entity: Option<ROQueryItem<'w, Self::ItemQuery>>,
         param: SystemParamItem<'w, '_, Self::Param>,
         pass: &mut TrackedRenderPass<'w>,
     ) -> RenderCommandResult;
@@ -220,13 +225,22 @@ macro_rules! render_command_tuple_impl {
             fn render<'w>(
                 _item: &P,
                 ($($view,)*): ROQueryItem<'w, Self::ViewQuery>,
-                ($($entity,)*): ROQueryItem<'w, Self::ItemQuery>,
+                maybe_entities: Option<ROQueryItem<'w, Self::ItemQuery>>,
                 ($($name,)*): SystemParamItem<'w, '_, Self::Param>,
                 _pass: &mut TrackedRenderPass<'w>,
             ) -> RenderCommandResult {
-                $(if let RenderCommandResult::Failure = $name::render(_item, $view, $entity, $name, _pass) {
-                    return RenderCommandResult::Failure;
-                })*
+                match maybe_entities {
+                    None => {
+                        $(if let RenderCommandResult::Failure = $name::render(_item, $view, None, $name, _pass) {
+                            return RenderCommandResult::Failure;
+                        })*
+                    }
+                    Some(($($entity,)*)) => {
+                        $(if let RenderCommandResult::Failure = $name::render(_item, $view, Some($entity), $name, _pass) {
+                            return RenderCommandResult::Failure;
+                        })*
+                    }
+                }
                 RenderCommandResult::Success
             }
         }
@@ -278,7 +292,7 @@ where
     ) {
         let param = self.state.get_manual(world);
         let view = self.view.get_manual(world, view).unwrap();
-        let entity = self.entity.get_manual(world, item.entity()).unwrap();
+        let entity = self.entity.get_manual(world, item.entity()).ok();
         // TODO: handle/log `RenderCommand` failure
         C::render(item, view, entity, param, pass);
     }

crates/bevy_render/src/render_phase/mod.rs

@@ -202,7 +202,7 @@ impl<P: CachedRenderPipelinePhaseItem> RenderCommand<P> for SetItemPipeline {
     fn render<'w>(
         item: &P,
         _view: (),
-        _entity: (),
+        _entity: Option<()>,
         pipeline_cache: SystemParamItem<'w, '_, Self::Param>,
         pass: &mut TrackedRenderPass<'w>,
     ) -> RenderCommandResult {

crates/bevy_sprite/src/mesh2d/material.rs

@@ -337,7 +337,7 @@ impl<P: PhaseItem, M: Material2d, const I: usize> RenderCommand<P>
     fn render<'w>(
         item: &P,
         _view: (),
-        _item_query: (),
+        _item_query: Option<()>,
         (materials, material_instances): SystemParamItem<'w, '_, Self::Param>,
         pass: &mut TrackedRenderPass<'w>,
     ) -> RenderCommandResult {

crates/bevy_sprite/src/mesh2d/mesh.rs

@@ -624,7 +624,7 @@ impl<P: PhaseItem, const I: usize> RenderCommand<P> for SetMesh2dViewBindGroup<I
     fn render<'w>(
         _item: &P,
         (view_uniform, mesh2d_view_bind_group): ROQueryItem<'w, Self::ViewQuery>,
-        _view: (),
+        _view: Option<()>,
         _param: SystemParamItem<'w, '_, Self::Param>,
         pass: &mut TrackedRenderPass<'w>,
     ) -> RenderCommandResult {
@@ -644,7 +644,7 @@ impl<P: PhaseItem, const I: usize> RenderCommand<P> for SetMesh2dBindGroup<I> {
     fn render<'w>(
         item: &P,
         _view: (),
-        _item_query: (),
+        _item_query: Option<()>,
         mesh2d_bind_group: SystemParamItem<'w, '_, Self::Param>,
         pass: &mut TrackedRenderPass<'w>,
     ) -> RenderCommandResult {
@@ -673,7 +673,7 @@ impl<P: PhaseItem> RenderCommand<P> for DrawMesh2d {
     fn render<'w>(
         item: &P,
         _view: (),
-        _item_query: (),
+        _item_query: Option<()>,
         (meshes, render_mesh2d_instances): SystemParamItem<'w, '_, Self::Param>,
         pass: &mut TrackedRenderPass<'w>,
     ) -> RenderCommandResult {

crates/bevy_sprite/src/render/mod.rs

@@ -752,7 +752,7 @@ impl<P: PhaseItem, const I: usize> RenderCommand<P> for SetSpriteViewBindGroup<I
     fn render<'w>(
         _item: &P,
         view_uniform: &'_ ViewUniformOffset,
-        _entity: (),
+        _entity: Option<()>,
         sprite_meta: SystemParamItem<'w, '_, Self::Param>,
         pass: &mut TrackedRenderPass<'w>,
     ) -> RenderCommandResult {
@@ -773,11 +773,14 @@ impl<P: PhaseItem, const I: usize> RenderCommand<P> for SetSpriteTextureBindGrou
     fn render<'w>(
         _item: &P,
         _view: (),
-        batch: &'_ SpriteBatch,
+        batch: Option<&'_ SpriteBatch>,
         image_bind_groups: SystemParamItem<'w, '_, Self::Param>,
         pass: &mut TrackedRenderPass<'w>,
     ) -> RenderCommandResult {
         let image_bind_groups = image_bind_groups.into_inner();
+        let Some(batch) = batch else {
+            return RenderCommandResult::Failure;
+        };
 
         pass.set_bind_group(
             I,
@@ -800,11 +803,15 @@ impl<P: PhaseItem> RenderCommand<P> for DrawSpriteBatch {
     fn render<'w>(
         _item: &P,
         _view: (),
-        batch: &'_ SpriteBatch,
+        batch: Option<&'_ SpriteBatch>,
         sprite_meta: SystemParamItem<'w, '_, Self::Param>,
         pass: &mut TrackedRenderPass<'w>,
     ) -> RenderCommandResult {
         let sprite_meta = sprite_meta.into_inner();
+        let Some(batch) = batch else {
+            return RenderCommandResult::Failure;
+        };
+
         pass.set_index_buffer(
             sprite_meta.sprite_index_buffer.buffer().unwrap().slice(..),
             0,

crates/bevy_ui/src/render/render_pass.rs

@@ -161,7 +161,7 @@ impl<P: PhaseItem, const I: usize> RenderCommand<P> for SetUiViewBindGroup<I> {
     fn render<'w>(
         _item: &P,
         view_uniform: &'w ViewUniformOffset,
-        _entity: (),
+        _entity: Option<()>,
         ui_meta: SystemParamItem<'w, '_, Self::Param>,
         pass: &mut TrackedRenderPass<'w>,
     ) -> RenderCommandResult {
@@ -183,11 +183,15 @@ impl<P: PhaseItem, const I: usize> RenderCommand<P> for SetUiTextureBindGroup<I>
     fn render<'w>(
         _item: &P,
         _view: (),
-        batch: &'w UiBatch,
+        batch: Option<&'w UiBatch>,
         image_bind_groups: SystemParamItem<'w, '_, Self::Param>,
         pass: &mut TrackedRenderPass<'w>,
     ) -> RenderCommandResult {
         let image_bind_groups = image_bind_groups.into_inner();
+        let Some(batch) = batch else {
+            return RenderCommandResult::Failure;
+        };
+
         pass.set_bind_group(I, image_bind_groups.values.get(&batch.image).unwrap(), &[]);
         RenderCommandResult::Success
     }
@@ -202,10 +206,14 @@ impl<P: PhaseItem> RenderCommand<P> for DrawUiNode {
     fn render<'w>(
         _item: &P,
         _view: (),
-        batch: &'w UiBatch,
+        batch: Option<&'w UiBatch>,
         ui_meta: SystemParamItem<'w, '_, Self::Param>,
         pass: &mut TrackedRenderPass<'w>,
     ) -> RenderCommandResult {
+        let Some(batch) = batch else {
+            return RenderCommandResult::Failure;
+        };
+
         pass.set_vertex_buffer(0, ui_meta.into_inner().vertices.buffer().unwrap().slice(..));
         pass.draw(batch.range.clone(), 0..1);
         RenderCommandResult::Success

crates/bevy_ui/src/render/ui_material_pipeline.rs

@@ -272,7 +272,7 @@ impl<P: PhaseItem, M: UiMaterial, const I: usize> RenderCommand<P> for SetMatUiV
     fn render<'w>(
         _item: &P,
         view_uniform: &'w ViewUniformOffset,
-        _entity: (),
+        _entity: Option<()>,
         ui_meta: SystemParamItem<'w, '_, Self::Param>,
         pass: &mut TrackedRenderPass<'w>,
     ) -> RenderCommandResult {
@@ -296,10 +296,13 @@ impl<P: PhaseItem, M: UiMaterial, const I: usize> RenderCommand<P>
     fn render<'w>(
         _item: &P,
         _view: (),
-        material_handle: ROQueryItem<'_, Self::ItemQuery>,
+        material_handle: Option<ROQueryItem<'_, Self::ItemQuery>>,
         materials: SystemParamItem<'w, '_, Self::Param>,
         pass: &mut TrackedRenderPass<'w>,
     ) -> RenderCommandResult {
+        let Some(material_handle) = material_handle else {
+            return RenderCommandResult::Failure;
+        };
         let Some(material) = materials.into_inner().get(&material_handle.material) else {
             return RenderCommandResult::Failure;
         };
@@ -318,10 +321,14 @@ impl<P: PhaseItem, M: UiMaterial> RenderCommand<P> for DrawUiMaterialNode<M> {
     fn render<'w>(
         _item: &P,
         _view: (),
-        batch: &'w UiMaterialBatch<M>,
+        batch: Option<&'w UiMaterialBatch<M>>,
         ui_meta: SystemParamItem<'w, '_, Self::Param>,
         pass: &mut TrackedRenderPass<'w>,
     ) -> RenderCommandResult {
+        let Some(batch) = batch else {
+            return RenderCommandResult::Failure;
+        };
+
         pass.set_vertex_buffer(0, ui_meta.into_inner().vertices.buffer().unwrap().slice(..));
         pass.draw(batch.range.clone(), 0..1);
         RenderCommandResult::Success

examples/shader/shader_instancing.rs

@@ -244,7 +244,7 @@ impl<P: PhaseItem> RenderCommand<P> for DrawMeshInstanced {
     fn render<'w>(
         item: &P,
         _view: (),
-        instance_buffer: &'w InstanceBuffer,
+        instance_buffer: Option<&'w InstanceBuffer>,
         (meshes, render_mesh_instances): SystemParamItem<'w, '_, Self::Param>,
         pass: &mut TrackedRenderPass<'w>,
     ) -> RenderCommandResult {
@@ -254,6 +254,9 @@ impl<P: PhaseItem> RenderCommand<P> for DrawMeshInstanced {
         let Some(gpu_mesh) = meshes.into_inner().get(mesh_instance.mesh_asset_id) else {
             return RenderCommandResult::Failure;
         };
+        let Some(instance_buffer) = instance_buffer else {
+            return RenderCommandResult::Failure;
+        };
 
         pass.set_vertex_buffer(0, gpu_mesh.vertex_buffer.slice(..));
         pass.set_vertex_buffer(1, instance_buffer.buffer.slice(..));