From a785e3c20dce1dfe822084f00be02641382a1a35 Mon Sep 17 00:00:00 2001
From: Patrick Walton <pcwalton@mimiga.net>
Date: Tue, 21 May 2024 15:06:25 -0700
Subject: [PATCH] Fix UI elements randomly not appearing after #13277. (#13462)

We invoked the `extract_default_ui_camera_view` system twice: once for
2D cameras and once for 3D cameras. This was fine before moving to
resources for render phases, but, after the move to resources, the first
thing such systems do is to clear out all the entities-to-be-rendered
from the previous frame. So, if the scheduler happened to run
`extract_default_ui_camera_view::<Camera2d>` first, then all the UI
elements that it queued would be overwritten by the
`extract_default_ui_camera_view::<Camera3d>` system, or vice versa. The
ordering dependence is the reason why this problem was intermittent.

This commit fixes the problem by merging the two systems into one
systems, using an `Or` query filter.

## Migration Guide

* The `bevy_ui::render::extract_default_ui_camera_view` system is no
longer parameterized over the specific type of camera and is hard-wired
to either `Camera2d` or `Camera3d` components.
---
 crates/bevy_ui/src/render/mod.rs | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/crates/bevy_ui/src/render/mod.rs b/crates/bevy_ui/src/render/mod.rs
index 1d7616bcf7..b71404c3a2 100644
--- a/crates/bevy_ui/src/render/mod.rs
+++ b/crates/bevy_ui/src/render/mod.rs
@@ -101,8 +101,7 @@ pub fn build_ui_render(app: &mut App) {
         .add_systems(
             ExtractSchedule,
             (
-                extract_default_ui_camera_view::<Camera2d>,
-                extract_default_ui_camera_view::<Camera3d>,
+                extract_default_ui_camera_view,
                 extract_uinode_background_colors.in_set(RenderUiSystem::ExtractBackgrounds),
                 extract_uinode_images.in_set(RenderUiSystem::ExtractImages),
                 extract_uinode_borders.in_set(RenderUiSystem::ExtractBorders),
@@ -657,11 +656,12 @@ const UI_CAMERA_TRANSFORM_OFFSET: f32 = -0.1;
 #[derive(Component)]
 pub struct DefaultCameraView(pub Entity);
 
-pub fn extract_default_ui_camera_view<T: Component>(
+/// Extracts all UI elements associated with a camera into the render world.
+pub fn extract_default_ui_camera_view(
     mut commands: Commands,
     mut transparent_render_phases: ResMut<ViewSortedRenderPhases<TransparentUi>>,
     ui_scale: Extract<Res<UiScale>>,
-    query: Extract<Query<(Entity, &Camera), With<T>>>,
+    query: Extract<Query<(Entity, &Camera), Or<(With<Camera2d>, With<Camera3d>)>>>,
     mut live_entities: Local<EntityHashSet>,
 ) {
     live_entities.clear();