From df26bc338701dd77f688328c71e0744f8763e8c9 Mon Sep 17 00:00:00 2001
From: HugoPeters1024 <hugo.peters@channable.com>
Date: Tue, 25 Mar 2025 05:48:49 +0100
Subject: [PATCH] bugfix(frustra of point lights were not recalculated when a
 camera changes) (#18519)

# Objective

- Fixes https://github.com/bevyengine/bevy/issues/11682

## Solution

- https://github.com/bevyengine/bevy/pull/4086 introduced an
optimization to not do redundant calculations, but did not take into
account changes to the resource `global_lights`. I believe that my patch
includes the optimization benefit but adds the required nuance to fix
said bug.

## Testing

The example originally given by
[@kirillsurkov](https://github.com/kirillsurkov) and then updated by me
to bevy 15.3 here:
https://github.com/bevyengine/bevy/issues/11682#issuecomment-2746287416
will not have shadows without this patch:

```rust
use bevy::prelude::*;

#[derive(Resource)]
struct State {
    x: f32,
}

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_systems(Startup, setup)
        .add_systems(Update, update)
        .insert_resource(State { x: -40.0 })
        .run();
}

fn setup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
) {
    commands.spawn((
        Mesh3d(meshes.add(Circle::new(4.0))),
        MeshMaterial3d(materials.add(Color::WHITE)),
    ));
    commands.spawn((
        Mesh3d(meshes.add(Cuboid::new(1.0, 1.0, 1.0))),
        MeshMaterial3d(materials.add(Color::linear_rgb(0.0, 1.0, 0.0))),
    ));
    commands.spawn((
        PointLight {
            shadows_enabled: true,
            ..default()
        },
        Transform::from_xyz(4.0, 8.0, 4.0),
    ));
    commands.spawn(Camera3d::default());
}

fn update(mut state: ResMut<State>, mut camera: Query<&mut Transform, With<Camera3d>>) {
    let mut camera = camera.single_mut().unwrap();

    let t = Vec3::new(state.x, 0.0, 10.0);
    camera.translation = t;
    camera.look_at(t - Vec3::Z, Vec3::Y);

    state.x = 0.0;
}
```

---------

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
Co-authored-by: JMS55 <47158642+JMS55@users.noreply.github.com>
---
 crates/bevy_pbr/src/light/mod.rs | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/crates/bevy_pbr/src/light/mod.rs b/crates/bevy_pbr/src/light/mod.rs
index 3f57464e21..bc893268dc 100644
--- a/crates/bevy_pbr/src/light/mod.rs
+++ b/crates/bevy_pbr/src/light/mod.rs
@@ -564,9 +564,13 @@ pub fn update_directional_light_frusta(
 // NOTE: Run this after assign_lights_to_clusters!
 pub fn update_point_light_frusta(
     global_lights: Res<GlobalVisibleClusterableObjects>,
-    mut views: Query<
-        (Entity, &GlobalTransform, &PointLight, &mut CubemapFrusta),
-        Or<(Changed<GlobalTransform>, Changed<PointLight>)>,
+    mut views: Query<(Entity, &GlobalTransform, &PointLight, &mut CubemapFrusta)>,
+    changed_lights: Query<
+        Entity,
+        (
+            With<PointLight>,
+            Or<(Changed<GlobalTransform>, Changed<PointLight>)>,
+        ),
     >,
 ) {
     let view_rotations = CUBE_MAP_FACES
@@ -575,6 +579,12 @@ pub fn update_point_light_frusta(
         .collect::<Vec<_>>();
 
     for (entity, transform, point_light, mut cubemap_frusta) in &mut views {
+        // If this light hasn't changed, and neither has the set of global_lights,
+        // then we can skip this calculation.
+        if !global_lights.is_changed() && !changed_lights.contains(entity) {
+            continue;
+        }
+
         // The frusta are used for culling meshes to the light for shadow mapping
         // so if shadow mapping is disabled for this light, then the frusta are
         // not needed.