From c3f72ba4ad4a005b4560029ad65bb4efc9ad74d5 Mon Sep 17 00:00:00 2001
From: ickshonpe <david.curthoys@googlemail.com>
Date: Sun, 23 Mar 2025 09:42:44 +0000
Subject: [PATCH] Skip camera look ups in queue uinodes  (#17668)

# Objective

`queue_uinodes` looks up the `ExtractedView` for every extracted UI
node, but there's no need to look it up again if consecutive nodes have
the same `extracted_camera_entity`.

## Solution

In queue uinodes reuse the previously looked up extracted view if the
`extracted_camera_entity` doesn't change

## Showcase

```
cargo run --example many_buttons --release --features "trace_tracy"
```

<img width="521" alt="queue-ui-improvement"
src="https://github.com/user-attachments/assets/2f111837-8c2e-4a6d-94cd-3c3462c58bc9"
/>

yellow is this PR, red is main
---
 crates/bevy_ui/src/render/mod.rs | 37 ++++++++++++++++++++------------
 1 file changed, 23 insertions(+), 14 deletions(-)

diff --git a/crates/bevy_ui/src/render/mod.rs b/crates/bevy_ui/src/render/mod.rs
index b5d24f194d..6f691d4163 100644
--- a/crates/bevy_ui/src/render/mod.rs
+++ b/crates/bevy_ui/src/render/mod.rs
@@ -946,26 +946,34 @@ pub fn queue_uinodes(
     ui_pipeline: Res<UiPipeline>,
     mut pipelines: ResMut<SpecializedRenderPipelines<UiPipeline>>,
     mut transparent_render_phases: ResMut<ViewSortedRenderPhases<TransparentUi>>,
-    mut render_views: Query<(&UiCameraView, Option<&UiAntiAlias>), With<ExtractedView>>,
+    render_views: Query<(&UiCameraView, Option<&UiAntiAlias>), With<ExtractedView>>,
     camera_views: Query<&ExtractedView>,
     pipeline_cache: Res<PipelineCache>,
     draw_functions: Res<DrawFunctions<TransparentUi>>,
 ) {
     let draw_function = draw_functions.read().id::<DrawUi>();
+    let mut current_camera_entity = Entity::PLACEHOLDER;
+    let mut current_phase = None;
+
     for (index, extracted_uinode) in extracted_uinodes.uinodes.iter().enumerate() {
-        let entity = extracted_uinode.render_entity;
-        let Ok((default_camera_view, ui_anti_alias)) =
-            render_views.get_mut(extracted_uinode.extracted_camera_entity)
-        else {
-            continue;
-        };
+        if current_camera_entity != extracted_uinode.extracted_camera_entity {
+            current_phase = render_views
+                .get(extracted_uinode.extracted_camera_entity)
+                .ok()
+                .and_then(|(default_camera_view, ui_anti_alias)| {
+                    camera_views
+                        .get(default_camera_view.0)
+                        .ok()
+                        .and_then(|view| {
+                            transparent_render_phases
+                                .get_mut(&view.retained_view_entity)
+                                .map(|transparent_phase| (view, ui_anti_alias, transparent_phase))
+                        })
+                });
+            current_camera_entity = extracted_uinode.extracted_camera_entity;
+        }
 
-        let Ok(view) = camera_views.get(default_camera_view.0) else {
-            continue;
-        };
-
-        let Some(transparent_phase) = transparent_render_phases.get_mut(&view.retained_view_entity)
-        else {
+        let Some((view, ui_anti_alias, transparent_phase)) = current_phase.as_mut() else {
             continue;
         };
 
@@ -977,10 +985,11 @@ pub fn queue_uinodes(
                 anti_alias: matches!(ui_anti_alias, None | Some(UiAntiAlias::On)),
             },
         );
+
         transparent_phase.add(TransparentUi {
             draw_function,
             pipeline,
-            entity: (entity, extracted_uinode.main_entity),
+            entity: (extracted_uinode.render_entity, extracted_uinode.main_entity),
             sort_key: FloatOrd(extracted_uinode.stack_index as f32 + stack_z_offsets::NODE),
             index,
             // batch_range will be calculated in prepare_uinodes