default UI camera extraction fix (#17100)

# Objective

In UI extraction the default UI camera is queried for every UI node. It
only needs to be retrieved once.

## Solution

Query for the default UI camera once before iterating the UI nodes.

```
cargo run --example many_buttons --release --features "trace_tracy"
```
<img width="631" alt="default-camera-extract"
src="https://github.com/user-attachments/assets/db712bce-6a0b-49a7-8e20-654baf588390"
/>

`extract_uinode_background_colors` yellow is this PR, red is main.

crates/bevy_ui/src/render/box_shadow.rs

@@ -251,10 +251,11 @@ pub fn extract_shadows(
     >,
     mapping: Extract<Query<RenderEntity>>,
 ) {
+    let default_camera_entity = default_ui_camera.get();
+
     for (entity, uinode, transform, view_visibility, box_shadow, clip, camera) in &box_shadow_query
     {
-        let Some(camera_entity) = camera.map(TargetCamera::entity).or(default_ui_camera.get())
+        let Some(camera_entity) = camera.map(TargetCamera::entity).or(default_camera_entity) else {
-        else {
             continue;
         };
 

crates/bevy_ui/src/render/debug_overlay.rs

@@ -76,13 +76,14 @@ pub fn extract_debug_overlay(
         return;
     }
 
+    let default_camera_entity = default_ui_camera.get();
+
     for (entity, uinode, visibility, maybe_clip, transform, camera) in &uinode_query {
         if !debug_options.show_hidden && !visibility.get() {
             continue;
         }
 
-        let Some(camera_entity) = camera.map(TargetCamera::entity).or(default_ui_camera.get())
+        let Some(camera_entity) = camera.map(TargetCamera::entity).or(default_camera_entity) else {
-        else {
             continue;
         };
 

crates/bevy_ui/src/render/mod.rs

@@ -267,11 +267,11 @@ pub fn extract_uinode_background_colors(
     >,
     mapping: Extract<Query<RenderEntity>>,
 ) {
+    let default_camera_entity = default_ui_camera.get();
     for (entity, uinode, transform, view_visibility, clip, camera, background_color) in
         &uinode_query
     {
-        let Some(camera_entity) = camera.map(TargetCamera::entity).or(default_ui_camera.get())
+        let Some(camera_entity) = camera.map(TargetCamera::entity).or(default_camera_entity) else {
-        else {
             continue;
         };
 
@@ -330,9 +330,9 @@ pub fn extract_uinode_images(
     >,
     mapping: Extract<Query<RenderEntity>>,
 ) {
+    let default_camera_entity = default_ui_camera.get();
     for (entity, uinode, transform, view_visibility, clip, camera, image) in &uinode_query {
-        let Some(camera_entity) = camera.map(TargetCamera::entity).or(default_ui_camera.get())
+        let Some(camera_entity) = camera.map(TargetCamera::entity).or(default_camera_entity) else {
-        else {
             continue;
         };
 
@@ -423,7 +423,7 @@ pub fn extract_uinode_borders(
     ui_children: UiChildren,
 ) {
     let image = AssetId::<Image>::default();
-
+    let default_camera_entity = default_ui_camera.get();
     for (
         entity,
         node,
@@ -437,7 +437,7 @@ pub fn extract_uinode_borders(
     {
         let Some(camera_entity) = maybe_camera
             .map(TargetCamera::entity)
-            .or(default_ui_camera.get())
+            .or(default_camera_entity)
         else {
             continue;
         };

crates/bevy_ui/src/render/ui_texture_slice_pipeline.rs

@@ -264,9 +264,10 @@ pub fn extract_ui_texture_slices(
     >,
     mapping: Extract<Query<RenderEntity>>,
 ) {
+    let default_camera_entity = default_ui_camera.get();
+
     for (entity, uinode, transform, view_visibility, clip, camera, image) in &slicers_query {
-        let Some(camera_entity) = camera.map(TargetCamera::entity).or(default_ui_camera.get())
+        let Some(camera_entity) = camera.map(TargetCamera::entity).or(default_camera_entity) else {
-        else {
             continue;
         };