ui materials respect target camera (#12183)

# Objective

fix #12182 

- extract (or default) target camera for ui material nodes in the same
way as for other material nodes
- render ui material nodes only to their specified target

crates/bevy_ui/src/render/ui_material_pipeline.rs

@@ -339,6 +339,10 @@ pub struct ExtractedUiMaterialNode<M: UiMaterial> {
     pub border: [f32; 4],
     pub material: AssetId<M>,
     pub clip: Option<Rect>,
+    // Camera to render this UI node to. By the time it is extracted,
+    // it is defaulted to a single camera if only one exists.
+    // Nodes with ambiguous camera will be ignored.
+    pub camera_entity: Entity,
 }
 
 #[derive(Resource)]
@@ -358,6 +362,7 @@ pub fn extract_ui_material_nodes<M: UiMaterial>(
     mut extracted_uinodes: ResMut<ExtractedUiMaterialNodes<M>>,
     materials: Extract<Res<Assets<M>>>,
     ui_stack: Extract<Res<UiStack>>,
+    default_ui_camera: Extract<DefaultUiCamera>,
     uinode_query: Extract<
         Query<
             (
@@ -368,6 +373,7 @@ pub fn extract_ui_material_nodes<M: UiMaterial>(
                 &Handle<M>,
                 &ViewVisibility,
                 Option<&CalculatedClip>,
+                Option<&TargetCamera>,
             ),
             Without<BackgroundColor>,
         >,
@@ -382,10 +388,19 @@ pub fn extract_ui_material_nodes<M: UiMaterial>(
         // The logical window resolution returned by `Window` only takes into account the window scale factor and not `UiScale`,
         // so we have to divide by `UiScale` to get the size of the UI viewport.
         / ui_scale.0;
+
+    // If there is only one camera, we use it as default
+    let default_single_camera = default_ui_camera.get();
+
     for (stack_index, entity) in ui_stack.uinodes.iter().enumerate() {
-        if let Ok((entity, uinode, style, transform, handle, view_visibility, clip)) =
+        if let Ok((entity, uinode, style, transform, handle, view_visibility, clip, camera)) =
             uinode_query.get(*entity)
         {
+            let Some(camera_entity) = camera.map(TargetCamera::entity).or(default_single_camera)
+            else {
+                continue;
+            };
+
             // skip invisible nodes
             if !view_visibility.get() {
                 continue;
@@ -428,6 +443,7 @@ pub fn extract_ui_material_nodes<M: UiMaterial>(
                     },
                     border: [left, right, top, bottom],
                     clip: clip.map(|clip| clip.clip),
+                    camera_entity,
                 },
             );
         };
@@ -747,7 +763,11 @@ pub fn queue_ui_material_nodes<M: UiMaterial>(
         let Some(material) = render_materials.get(&extracted_uinode.material) else {
             continue;
         };
-        for (view, mut transparent_phase) in &mut views {
+        let Ok((view, mut transparent_phase)) = views.get_mut(extracted_uinode.camera_entity)
+        else {
+            continue;
+        };
+
         let pipeline = pipelines.specialize(
             &pipeline_cache,
             &ui_material_pipeline,
@@ -771,5 +791,4 @@ pub fn queue_ui_material_nodes<M: UiMaterial>(
             dynamic_offset: None,
         });
     }
-    }
 }