From ffad06519047d86d10fdc4f1e48f7a7c01b815a7 Mon Sep 17 00:00:00 2001
From: Robert Swain <robert.swain@gmail.com>
Date: Wed, 23 Mar 2022 18:52:59 +0100
Subject: [PATCH] examples: Add many_lights example for testing many point
 lights

---
 Cargo.toml                 |   4 +
 examples/3d/many_lights.rs | 166 +++++++++++++++++++++++++++++++++++++
 examples/README.md         |   1 +
 3 files changed, 171 insertions(+)
 create mode 100644 examples/3d/many_lights.rs

diff --git a/Cargo.toml b/Cargo.toml
index 6577c9317ea953..7e771ddc56d478 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -191,6 +191,10 @@ path = "examples/3d/manual_gltf_animation_player.rs"
 name = "many_cubes"
 path = "examples/3d/many_cubes.rs"
 
+[[example]]
+name = "many_lights"
+path = "examples/3d/many_lights.rs"
+
 [[example]]
 name = "msaa"
 path = "examples/3d/msaa.rs"
diff --git a/examples/3d/many_lights.rs b/examples/3d/many_lights.rs
new file mode 100644
index 00000000000000..6134b459de082d
--- /dev/null
+++ b/examples/3d/many_lights.rs
@@ -0,0 +1,166 @@
+use bevy::{
+    diagnostic::{FrameTimeDiagnosticsPlugin, LogDiagnosticsPlugin},
+    math::{DVec2, DVec3},
+    pbr::{ExtractedPointLight, GlobalLightMeta},
+    prelude::*,
+    render::{RenderApp, RenderStage},
+};
+
+fn main() {
+    App::new()
+        .insert_resource(WindowDescriptor {
+            width: 1024.0,
+            height: 768.0,
+            title: "many_lights".to_string(),
+            present_mode: bevy::window::PresentMode::Immediate,
+            ..default()
+        })
+        .add_plugins(DefaultPlugins)
+        .add_plugin(FrameTimeDiagnosticsPlugin::default())
+        .add_plugin(LogDiagnosticsPlugin::default())
+        .add_startup_system(setup)
+        .add_system(move_camera)
+        .add_system(print_light_count)
+        .add_plugin(LogVisibleLights)
+        .run();
+}
+
+fn setup(
+    mut commands: Commands,
+    mut meshes: ResMut<Assets<Mesh>>,
+    mut materials: ResMut<Assets<StandardMaterial>>,
+) {
+    const LIGHT_RADIUS: f32 = 0.3;
+    const LIGHT_INTENSITY: f32 = 5.0;
+    const RADIUS: f32 = 50.0;
+    const N_LIGHTS: usize = 100_000;
+
+    commands.spawn_bundle(PbrBundle {
+        mesh: meshes.add(Mesh::from(shape::Icosphere {
+            radius: RADIUS,
+            subdivisions: 9,
+        })),
+        material: materials.add(StandardMaterial::from(Color::WHITE)),
+        transform: Transform::from_scale(Vec3::splat(-1.0)),
+        ..default()
+    });
+
+    let mesh = meshes.add(Mesh::from(shape::Cube { size: 1.0 }));
+    let material = materials.add(StandardMaterial {
+        base_color: Color::PINK,
+        ..default()
+    });
+
+    // NOTE: This pattern is good for testing performance of culling as it provides roughly
+    // the same number of visible meshes regardless of the viewing angle.
+    // NOTE: f64 is used to avoid precision issues that produce visual artifacts in the distribution
+    let golden_ratio = 0.5f64 * (1.0f64 + 5.0f64.sqrt());
+    for i in 0..N_LIGHTS {
+        let spherical_polar_theta_phi = fibonacci_spiral_on_sphere(golden_ratio, i, N_LIGHTS);
+        let unit_sphere_p = spherical_polar_to_cartesian(spherical_polar_theta_phi);
+        commands.spawn_bundle(PointLightBundle {
+            point_light: PointLight {
+                range: LIGHT_RADIUS,
+                intensity: LIGHT_INTENSITY,
+                ..default()
+            },
+            transform: Transform::from_translation((RADIUS as f64 * unit_sphere_p).as_vec3()),
+            ..default()
+        });
+    }
+
+    // camera
+    commands.spawn_bundle(PerspectiveCameraBundle::default());
+
+    // add one cube, the only one with strong handles
+    // also serves as a reference point during rotation
+    commands.spawn_bundle(PbrBundle {
+        mesh,
+        material,
+        transform: Transform {
+            translation: Vec3::new(0.0, RADIUS as f32, 0.0),
+            scale: Vec3::splat(5.0),
+            ..default()
+        },
+        ..default()
+    });
+}
+
+// NOTE: This epsilon value is apparently optimal for optimizing for the average
+// nearest-neighbor distance. See:
+// http://extremelearning.com.au/how-to-evenly-distribute-points-on-a-sphere-more-effectively-than-the-canonical-fibonacci-lattice/
+// for details.
+const EPSILON: f64 = 0.36;
+fn fibonacci_spiral_on_sphere(golden_ratio: f64, i: usize, n: usize) -> DVec2 {
+    DVec2::new(
+        2.0 * std::f64::consts::PI * (i as f64 / golden_ratio),
+        (1.0 - 2.0 * (i as f64 + EPSILON) / (n as f64 - 1.0 + 2.0 * EPSILON)).acos(),
+    )
+}
+
+fn spherical_polar_to_cartesian(p: DVec2) -> DVec3 {
+    let (sin_theta, cos_theta) = p.x.sin_cos();
+    let (sin_phi, cos_phi) = p.y.sin_cos();
+    DVec3::new(cos_theta * sin_phi, sin_theta * sin_phi, cos_phi)
+}
+
+// System for rotating the camera
+fn move_camera(time: Res<Time>, mut camera_query: Query<&mut Transform, With<Camera>>) {
+    let mut camera_transform = camera_query.single_mut();
+    camera_transform.rotate(Quat::from_rotation_z(time.delta_seconds() * 0.15));
+    camera_transform.rotate(Quat::from_rotation_x(time.delta_seconds() * 0.15));
+}
+
+// System for printing the number of meshes on every tick of the timer
+fn print_light_count(time: Res<Time>, mut timer: Local<PrintingTimer>, lights: Query<&PointLight>) {
+    timer.0.tick(time.delta());
+
+    if timer.0.just_finished() {
+        info!("Lights: {}", lights.iter().len(),);
+    }
+}
+
+struct LogVisibleLights;
+
+impl Plugin for LogVisibleLights {
+    fn build(&self, app: &mut App) {
+        let render_app = match app.get_sub_app_mut(RenderApp) {
+            Ok(render_app) => render_app,
+            Err(_) => return,
+        };
+
+        render_app
+            .add_system_to_stage(RenderStage::Extract, extract_time)
+            .add_system_to_stage(RenderStage::Prepare, print_visible_light_count);
+    }
+}
+
+// System for printing the number of meshes on every tick of the timer
+fn print_visible_light_count(
+    time: Res<Time>,
+    mut timer: Local<PrintingTimer>,
+    visible: Query<&ExtractedPointLight>,
+    global_light_meta: Res<GlobalLightMeta>,
+) {
+    timer.0.tick(time.delta());
+
+    if timer.0.just_finished() {
+        info!(
+            "Visible Lights: {}, Rendered Lights: {}",
+            visible.iter().len(),
+            global_light_meta.entity_to_index.len()
+        );
+    }
+}
+
+fn extract_time(mut commands: Commands, time: Res<Time>) {
+    commands.insert_resource(time.into_inner().clone());
+}
+
+struct PrintingTimer(Timer);
+
+impl Default for PrintingTimer {
+    fn default() -> Self {
+        Self(Timer::from_seconds(1.0, true))
+    }
+}
diff --git a/examples/README.md b/examples/README.md
index 5342f9d4d288ca..5150d73724b1f7 100644
--- a/examples/README.md
+++ b/examples/README.md
@@ -106,6 +106,7 @@ Example | File | Description
 `load_gltf` | [`3d/load_gltf.rs`](./3d/load_gltf.rs) | Loads and renders a gltf file as a scene
 `manual_gltf_animation_player` | [`3d/manual_gltf_animation_player.rs`](./3d/manual_gltf_animation_player.rs) | Loads and manually renders a gltf file with animations
 `many_cubes` | [`3d/many_cubes.rs`](./3d/many_cubes.rs) | Simple benchmark to test per-entity draw overhead
+`many_lights` | [`3d/many_lights.rs`](./3d/many_lights.rs) | Simple benchmark to test rendering many point lights
 `msaa` | [`3d/msaa.rs`](./3d/msaa.rs) | Configures MSAA (Multi-Sample Anti-Aliasing) for smoother edges
 `orthographic` | [`3d/orthographic.rs`](./3d/orthographic.rs) | Shows how to create a 3D orthographic view (for isometric-look games or CAD applications)
 `parenting` | [`3d/parenting.rs`](./3d/parenting.rs) | Demonstrates parent->child relationships and relative transformations