CameraProjection::compute_frustum (bevyengine#11139)

Frustum computation is nontrivial amount of code private in
`update_frusta` system.

Make it public.

This is needed to decide which entities to spawn/despawn in `Update`
based on camera changes. But if `Update` also changed camera, frustum is
not yet recomputed.

Technically it is probably possible to run an iteration of
`update_frusta` system by a user in `Update` schedule after propagating
`GlobalTransform` to the cameras, but it is easier to just compute
frustum manually using API added in this PR.

Also replace two places where this code is used.

---------

Co-authored-by: vero <email@atlasdostal.com>

crates/bevy_core_pipeline/src/core_2d/camera_2d.rs

@@ -45,14 +45,7 @@ impl Default for Camera2dBundle {
             ..Default::default()
         };
         let transform = Transform::default();
-        let view_projection =
-            projection.get_projection_matrix() * transform.compute_matrix().inverse();
-        let frustum = Frustum::from_view_projection_custom_far(
-            &view_projection,
-            &transform.translation,
-            &transform.back(),
-            projection.far(),
-        );
+        let frustum = projection.compute_frustum(&GlobalTransform::from(transform));
         Self {
             camera_render_graph: CameraRenderGraph::new(SubGraph2d),
             projection,
@@ -84,14 +77,7 @@ impl Camera2dBundle {
             ..Default::default()
         };
         let transform = Transform::from_xyz(0.0, 0.0, far - 0.1);
-        let view_projection =
-            projection.get_projection_matrix() * transform.compute_matrix().inverse();
-        let frustum = Frustum::from_view_projection_custom_far(
-            &view_projection,
-            &transform.translation,
-            &transform.back(),
-            projection.far(),
-        );
+        let frustum = projection.compute_frustum(&GlobalTransform::from(transform));
         Self {
             camera_render_graph: CameraRenderGraph::new(SubGraph3d),
             projection,

crates/bevy_render/src/camera/projection.rs

@@ -1,12 +1,14 @@
 use std::marker::PhantomData;
 use std::ops::{Div, DivAssign, Mul, MulAssign};
 
+use crate::primitives::Frustum;
 use bevy_app::{App, Plugin, PostStartup, PostUpdate};
 use bevy_ecs::{prelude::*, reflect::ReflectComponent};
 use bevy_math::{AspectRatio, Mat4, Rect, Vec2, Vec3A};
 use bevy_reflect::{
     std_traits::ReflectDefault, GetTypeRegistration, Reflect, ReflectDeserialize, ReflectSerialize,
 };
+use bevy_transform::components::GlobalTransform;
 use serde::{Deserialize, Serialize};
 
 /// Adds [`Camera`](crate::camera::Camera) driver systems for a given projection type.
@@ -60,6 +62,21 @@ pub trait CameraProjection {
     fn update(&mut self, width: f32, height: f32);
     fn far(&self) -> f32;
     fn get_frustum_corners(&self, z_near: f32, z_far: f32) -> [Vec3A; 8];
+
+    /// Compute camera frustum for camera with given projection and transform.
+    ///
+    /// This code is called by [`update_frusta`](crate::view::visibility::update_frusta) system
+    /// for each camera to update its frustum.
+    fn compute_frustum(&self, camera_transform: &GlobalTransform) -> Frustum {
+        let view_projection =
+            self.get_projection_matrix() * camera_transform.compute_matrix().inverse();
+        Frustum::from_view_projection_custom_far(
+            &view_projection,
+            &camera_transform.translation(),
+            &camera_transform.back(),
+            self.far(),
+        )
+    }
 }
 
 /// A configurable [`CameraProjection`] that can select its projection type at runtime.

crates/bevy_render/src/view/visibility/mod.rs

@@ -281,14 +281,7 @@ pub fn update_frusta<T: Component + CameraProjection + Send + Sync + 'static>(
     >,
 ) {
     for (transform, projection, mut frustum) in &mut views {
-        let view_projection =
-            projection.get_projection_matrix() * transform.compute_matrix().inverse();
-        *frustum = Frustum::from_view_projection_custom_far(
-            &view_projection,
-            &transform.translation(),
-            &transform.back(),
-            projection.far(),
-        );
+        *frustum = projection.compute_frustum(transform);
     }
 }