From 74c97332a68177849bd73bbbb2df6a8377049476 Mon Sep 17 00:00:00 2001
From: Torstein Grindvik <52322338+torsteingrindvik@users.noreply.github.com>
Date: Tue, 14 Nov 2023 03:13:21 +0100
Subject: [PATCH] Ignore inactive cameras (#10543)

# Objective

Currently, if a large amount of inactive cameras are spawned, they will
immensely slow down performance.

This can be reproduced by adding

```rust
    let default_image = images.add(default());
    for _ in 0..10000 {
        commands.spawn(Camera3dBundle {
            camera: Camera {
                is_active: false,
                target: RenderTarget::Image(default_image.clone()),
                ..default()
            },
            ..default()
        });
    }
```

to for example `3d_shapes`.

Using `tracy`, it's clear that preparing view bind groups for all
cameras is still happening.
Also, visibility checks on the extracted views from inactive cameras
also take place.

## Performance gains

The following `tracy` comparisons show the effect of skipping this
unneeded work.
Yellow is Bevy main, red is with the fix.

### Visibility checks


![bevy-visibility-check-savings](https://github.com/bevyengine/bevy/assets/52322338/154a20ce-bd70-487e-a85c-8b993950ea2b)

### Bind group preparation


![bevy-mesh2d-savings](https://github.com/bevyengine/bevy/assets/52322338/a48d8d9a-8c37-4c34-9698-b1b1bf01f070)


## Solution

- Check if the cameras are inactive in the appropriate places, and if so
skip them

## Changelog

### Changed

- Do not extract views from inactive cameras or check visiblity from
their extracted views

Signed-off-by: Torstein Grindvik <torstein.grindvik@muybridge.com>
Co-authored-by: Torstein Grindvik <torstein.grindvik@muybridge.com>
---
 crates/bevy_render/src/view/visibility/mod.rs | 13 +++++++++++--
 crates/bevy_ui/src/render/mod.rs              |  5 +++++
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/crates/bevy_render/src/view/visibility/mod.rs b/crates/bevy_render/src/view/visibility/mod.rs
index 0bd224f4d4..49bb64b689 100644
--- a/crates/bevy_render/src/view/visibility/mod.rs
+++ b/crates/bevy_render/src/view/visibility/mod.rs
@@ -384,7 +384,12 @@ fn reset_view_visibility(mut query: Query<&mut ViewVisibility>) {
 /// for that view.
 pub fn check_visibility(
     mut thread_queues: Local<ThreadLocal<Cell<Vec<Entity>>>>,
-    mut view_query: Query<(&mut VisibleEntities, &Frustum, Option<&RenderLayers>), With<Camera>>,
+    mut view_query: Query<(
+        &mut VisibleEntities,
+        &Frustum,
+        Option<&RenderLayers>,
+        &Camera,
+    )>,
     mut visible_aabb_query: Query<(
         Entity,
         &InheritedVisibility,
@@ -395,7 +400,11 @@ pub fn check_visibility(
         Has<NoFrustumCulling>,
     )>,
 ) {
-    for (mut visible_entities, frustum, maybe_view_mask) in &mut view_query {
+    for (mut visible_entities, frustum, maybe_view_mask, camera) in &mut view_query {
+        if !camera.is_active {
+            continue;
+        }
+
         let view_mask = maybe_view_mask.copied().unwrap_or_default();
 
         visible_entities.entities.clear();
diff --git a/crates/bevy_ui/src/render/mod.rs b/crates/bevy_ui/src/render/mod.rs
index f63fd1a0dc..b86f6544e6 100644
--- a/crates/bevy_ui/src/render/mod.rs
+++ b/crates/bevy_ui/src/render/mod.rs
@@ -551,6 +551,11 @@ pub fn extract_default_ui_camera_view<T: Component>(
         if matches!(camera_ui, Some(&UiCameraConfig { show_ui: false, .. })) {
             continue;
         }
+        // ignore inactive cameras
+        if !camera.is_active {
+            continue;
+        }
+
         if let (
             Some(logical_size),
             Some(URect {