From 55da315432074e32a28b1ef0ad39b8eadf92467a Mon Sep 17 00:00:00 2001
From: Robert Swain <robert.swain@gmail.com>
Date: Mon, 17 Jan 2022 22:55:44 +0000
Subject: [PATCH] bevy_render: Provide a way to opt-out of the built-in frustum
 culling (#3711)

# Objective

- Allow opting-out of the built-in frustum culling for cases where its behaviour would be incorrect
- Make use of the this in the shader_instancing example that uses a custom instancing method. The built-in frustum culling breaks the custom instancing in the shader_instancing example if the camera is moved to:

```rust
    commands.spawn_bundle(PerspectiveCameraBundle {
        transform: Transform::from_xyz(12.0, 0.0, 15.0)
            .looking_at(Vec3::new(12.0, 0.0, 0.0), Vec3::Y),
        ..Default::default()
    });
```

...such that the Aabb of the cube Mesh that is at the origin goes completely out of view. This incorrectly (for the purpose of the custom instancing) culls the `Mesh` and so culls all instances even though some may be visible.


## Solution

- Add a `NoFrustumCulling` marker component
- Do not compute and add an `Aabb` to `Mesh` entities without an `Aabb` if they have a `NoFrustumCulling` marker component
- Do not apply frustum culling to entities with the `NoFrustumCulling` marker component
---
 crates/bevy_render/src/view/visibility/mod.rs | 12 ++++++++++--
 examples/shader/shader_instancing.rs          | 10 +++++++++-
 2 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/crates/bevy_render/src/view/visibility/mod.rs b/crates/bevy_render/src/view/visibility/mod.rs
index 61da101d02d3e..cec6525d1acf2 100644
--- a/crates/bevy_render/src/view/visibility/mod.rs
+++ b/crates/bevy_render/src/view/visibility/mod.rs
@@ -40,6 +40,10 @@ impl Default for ComputedVisibility {
     }
 }
 
+/// Use this component to opt-out of built-in frustum culling for Mesh entities
+#[derive(Component)]
+pub struct NoFrustumCulling;
+
 #[derive(Clone, Component, Default, Debug, Reflect)]
 #[reflect(Component)]
 pub struct VisibleEntities {
@@ -106,7 +110,7 @@ impl Plugin for VisibilityPlugin {
 pub fn calculate_bounds(
     mut commands: Commands,
     meshes: Res<Assets<Mesh>>,
-    without_aabb: Query<(Entity, &Handle<Mesh>), Without<Aabb>>,
+    without_aabb: Query<(Entity, &Handle<Mesh>), (Without<Aabb>, Without<NoFrustumCulling>)>,
 ) {
     for (entity, mesh_handle) in without_aabb.iter() {
         if let Some(mesh) = meshes.get(mesh_handle) {
@@ -142,6 +146,7 @@ pub fn check_visibility(
             &mut ComputedVisibility,
             Option<&RenderLayers>,
             Option<&Aabb>,
+            Option<&NoFrustumCulling>,
             Option<&GlobalTransform>,
         )>,
     )>,
@@ -161,6 +166,7 @@ pub fn check_visibility(
             mut computed_visibility,
             maybe_entity_mask,
             maybe_aabb,
+            maybe_no_frustum_culling,
             maybe_transform,
         ) in visible_entity_query.q1().iter_mut()
         {
@@ -174,7 +180,9 @@ pub fn check_visibility(
             }
 
             // If we have an aabb and transform, do frustum culling
-            if let (Some(aabb), Some(transform)) = (maybe_aabb, maybe_transform) {
+            if let (Some(aabb), None, Some(transform)) =
+                (maybe_aabb, maybe_no_frustum_culling, maybe_transform)
+            {
                 if !frustum.intersects_obb(aabb, &transform.compute_matrix()) {
                     continue;
                 }
diff --git a/examples/shader/shader_instancing.rs b/examples/shader/shader_instancing.rs
index fee46581d4e63..9c5a048ea6107 100644
--- a/examples/shader/shader_instancing.rs
+++ b/examples/shader/shader_instancing.rs
@@ -14,7 +14,7 @@ use bevy::{
         },
         render_resource::*,
         renderer::RenderDevice,
-        view::{ComputedVisibility, ExtractedView, Msaa, Visibility},
+        view::{ComputedVisibility, ExtractedView, Msaa, NoFrustumCulling, Visibility},
         RenderApp, RenderStage,
     },
 };
@@ -45,6 +45,14 @@ fn setup(mut commands: Commands, mut meshes: ResMut<Assets<Mesh>>) {
         ),
         Visibility::default(),
         ComputedVisibility::default(),
+        // NOTE: Frustum culling is done based on the Aabb of the Mesh and the GlobalTransform.
+        // As the cube is at the origin, if its Aabb moves outside the view frustum, all the
+        // instanced cubes will be culled.
+        // The InstanceMaterialData contains the 'GlobalTransform' information for this custom
+        // instancing, and that is not taken into account with the built-in frustum culling.
+        // We must disable the built-in frustum culling by adding the `NoFrustumCulling` marker
+        // component to avoid incorrect culling.
+        NoFrustumCulling,
     ));
 
     // camera