From 00655b2986226b16221e512497034b73f5a96a67 Mon Sep 17 00:00:00 2001
From: Nicola Papale <nico@nicopap.ch>
Date: Sat, 9 Jul 2022 19:36:55 +0200
Subject: [PATCH] Make the ui cam extract system immutable

Following #4402, it is now impossible to mutate the main world from the
render world, so we split the update to the projection into a different
system ran in the main world.
---
 crates/bevy_ui/src/lib.rs        |  8 +++++++-
 crates/bevy_ui/src/render/mod.rs | 19 +++++--------------
 crates/bevy_ui/src/update.rs     | 17 ++++++++++++++++-
 3 files changed, 28 insertions(+), 16 deletions(-)

diff --git a/crates/bevy_ui/src/lib.rs b/crates/bevy_ui/src/lib.rs
index d72c1b83495d16..301392896d514d 100644
--- a/crates/bevy_ui/src/lib.rs
+++ b/crates/bevy_ui/src/lib.rs
@@ -29,7 +29,7 @@ use bevy_ecs::schedule::{ParallelSystemDescriptorCoercion, SystemLabel};
 use bevy_input::InputSystem;
 use bevy_transform::TransformSystem;
 use bevy_window::ModifiesWindows;
-use update::{ui_z_system, update_clipping_system};
+use update::{ui_z_system, update_clipping_system, update_ui_camera_perspective};
 
 /// The basic plugin for Bevy UI
 #[derive(Default)]
@@ -42,6 +42,8 @@ pub enum UiSystem {
     Flex,
     /// After this label, input interactions with UI entities have been updated for this frame
     Focus,
+    /// Update Ui camera perspective to fit new viewport logical size.
+    UpdateUiCameraPerspective,
 }
 
 impl Plugin for UiPlugin {
@@ -87,6 +89,10 @@ impl Plugin for UiPlugin {
                 CoreStage::PostUpdate,
                 widget::image_node_system.before(UiSystem::Flex),
             )
+            .add_system_to_stage(
+                CoreStage::Last,
+                update_ui_camera_perspective.label(UiSystem::UpdateUiCameraPerspective),
+            )
             .add_system_to_stage(
                 CoreStage::PostUpdate,
                 flex_node_system
diff --git a/crates/bevy_ui/src/render/mod.rs b/crates/bevy_ui/src/render/mod.rs
index d4e610071f09b8..fcd932e9f0072b 100644
--- a/crates/bevy_ui/src/render/mod.rs
+++ b/crates/bevy_ui/src/render/mod.rs
@@ -233,28 +233,19 @@ pub struct UiCamera {
 
 pub fn extract_default_ui_camera_view<T: Component>(
     mut commands: Commands,
-    mut query: Extract<Query<(Entity, &Camera, Option<&mut UiCameraConfig>), With<T>>>,
+    query: Extract<Query<(Entity, &Camera, Option<&UiCameraConfig>), With<T>>>,
 ) {
-    for (camera_entity, camera, opt_ui_config) in query.iter_mut() {
-        let ui_config = opt_ui_config.as_deref().cloned().unwrap_or_default();
+    for (camera_entity, camera, opt_ui_config) in query.iter() {
+        let ui_config = opt_ui_config.cloned().unwrap_or_default();
         // ignore cameras with disabled ui
         if !ui_config.show_ui {
             continue;
         }
-        if let (Some(logical_size), Some(physical_size)) = (
-            camera.logical_viewport_size(),
-            camera.physical_viewport_size(),
-        ) {
-            let mut projection = ui_config.projection.clone();
-            projection.update(logical_size.x, logical_size.y);
-            let projection_matrix = projection.get_projection_matrix();
-            if let Some(mut config_to_update) = opt_ui_config {
-                config_to_update.projection = projection;
-            }
+        if let Some(physical_size) = camera.physical_viewport_size() {
             let ui_camera = commands
                 .spawn()
                 .insert(ExtractedView {
-                    projection: projection_matrix,
+                    projection: ui_config.projection.get_projection_matrix(),
                     transform: GlobalTransform::from_xyz(
                         ui_config.position.x,
                         ui_config.position.y,
diff --git a/crates/bevy_ui/src/update.rs b/crates/bevy_ui/src/update.rs
index 05628555f1980b..04b1523412c61f 100644
--- a/crates/bevy_ui/src/update.rs
+++ b/crates/bevy_ui/src/update.rs
@@ -1,15 +1,17 @@
 //! This module contains systems that update the UI when something changes
 
-use crate::{CalculatedClip, Overflow, Style};
+use crate::{prelude::UiCameraConfig, CalculatedClip, Overflow, Style};
 
 use super::Node;
 use bevy_ecs::{
     entity::Entity,
+    prelude::{Changed, Or},
     query::{With, Without},
     system::{Commands, Query},
 };
 use bevy_hierarchy::{Children, Parent};
 use bevy_math::Vec2;
+use bevy_render::camera::{Camera, CameraProjection};
 use bevy_sprite::Rect;
 use bevy_transform::components::{GlobalTransform, Transform};
 
@@ -82,6 +84,19 @@ pub fn update_clipping_system(
     }
 }
 
+pub fn update_ui_camera_perspective(
+    mut query: Query<
+        (&Camera, &mut UiCameraConfig),
+        Or<(Changed<Camera>, Changed<UiCameraConfig>)>,
+    >,
+) {
+    for (camera, mut ui_config) in query.iter_mut() {
+        if let Some(logical_size) = camera.logical_viewport_size() {
+            ui_config.projection.update(logical_size.x, logical_size.y);
+        }
+    }
+}
+
 fn update_clipping(
     commands: &mut Commands,
     children_query: &Query<&Children>,