Allow user to choose default ui camera

crates/bevy_ui/src/ui_node.rs

@@ -1844,22 +1844,31 @@ impl TargetCamera {
     }
 }
 
+#[derive(Component)]
+/// Marker used to demarcate default cameras, they will have priority over `PrimaryWindow` cameras
+pub struct UiDefaultCamera;
+
 #[derive(SystemParam)]
 pub struct DefaultUiCamera<'w, 's> {
     cameras: Query<'w, 's, (Entity, &'static Camera)>,
+    default_cameras: Query<'w, 's, Entity, (With<Camera>, With<UiDefaultCamera>)>,
     primary_window: Query<'w, 's, Entity, With<PrimaryWindow>>,
 }
 
 impl<'w, 's> DefaultUiCamera<'w, 's> {
     pub fn get(&self) -> Option<Entity> {
-        self.cameras
-            .iter()
-            .filter(|(_, c)| match c.target {
-                RenderTarget::Window(WindowRef::Primary) => true,
-                RenderTarget::Window(WindowRef::Entity(w)) => self.primary_window.get(w).is_ok(),
-                _ => false,
-            })
-            .max_by_key(|(e, c)| (c.order, *e))
-            .map(|(e, _)| e)
+        self.default_cameras.get_single().ok().or_else(|| {
+            self.cameras
+                .iter()
+                .filter(|(_, c)| match c.target {
+                    RenderTarget::Window(WindowRef::Primary) => true,
+                    RenderTarget::Window(WindowRef::Entity(w)) => {
+                        self.primary_window.get(w).is_ok()
+                    }
+                    _ => false,
+                })
+                .max_by_key(|(e, c)| (c.order, *e))
+                .map(|(e, _)| e)
+        })
     }
 }