Add many_meshlet_materials stress test example

Author: CrazyRoka

Cargo.toml

@@ -3544,6 +3544,19 @@ description = "Displays many Text2d! Used for performance testing."
 category = "Stress Tests"
 wasm = true
 
+[[example]]
+name = "many_meshlet_materials"
+path = "examples/stress_tests/many_meshlet_materials.rs"
+doc-scrape-examples = true
+required-features = ["meshlet", "https"]
+
+[package.metadata.example.many_meshlet_materials]
+name = "Many Meshlet Materials"
+description = "Benchmark to test rendering many meshlet materials (experimental)"
+category = "Stress Tests"
+# Requires compute shaders and WGPU extensions, not supported by WebGL nor WebGPU.
+wasm = false
+
 [[example]]
 name = "many_materials"
 path = "examples/stress_tests/many_materials.rs"

examples/stress_tests/many_meshlet_materials.rs

@@ -0,0 +1,120 @@
+//! A stress test for the Meshlet pipeline specialization overhead.
+//!
+//! Run with `--unique-materials` to trigger the unconditional specialization bug.
+//! Run without it (shared material) to see the baseline performance.
+
+use argh::FromArgs;
+use bevy::{
+    pbr::experimental::meshlet::{MeshletMesh3d, MeshletPlugin},
+    prelude::*,
+    winit::WinitSettings,
+};
+
+#[derive(FromArgs, Resource)]
+#[argh(description = "Meshlet Material Stress Test")]
+struct Args {
+    /// the grid size (e.g., 50 means 50x50 = 2500 meshlets)
+    #[argh(option, short = 'n', default = "50")]
+    grid_size: usize,
+
+    /// if set, every meshlet gets a unique material asset.
+    /// This triggers the unconditional pipeline specialization bug in `prepare_material_meshlet_meshes`.
+    #[argh(switch)]
+    unique_materials: bool,
+}
+
+const ASSET_URL: &str =
+    "https://github.com/bevyengine/bevy_asset_files/raw/6dccaef517bde74d1969734703709aead7211dbc/meshlet/bunny.meshlet_mesh";
+
+fn main() {
+    let args: Args = argh::from_env();
+
+    println!("Meshlet Stress Test");
+    println!(
+        "Grid size: {}x{} ({} instances)",
+        args.grid_size,
+        args.grid_size,
+        args.grid_size * args.grid_size
+    );
+    println!(
+        "Materials: {}",
+        if args.unique_materials {
+            "UNIQUE"
+        } else {
+            "SHARED"
+        }
+    );
+
+    App::new()
+        .add_plugins((
+            DefaultPlugins,
+            MeshletPlugin {
+                cluster_buffer_slots: 8192,
+            },
+        ))
+        .insert_resource(WinitSettings::continuous())
+        .insert_resource(args)
+        .add_systems(Startup, setup)
+        .run();
+}
+
+fn setup(
+    mut commands: Commands,
+    args: Res<Args>,
+    asset_server: Res<AssetServer>,
+    mut materials: ResMut<Assets<StandardMaterial>>,
+) {
+    let meshlet_handle = asset_server.load(ASSET_URL);
+
+    let n = args.grid_size;
+    let spacing = 2.0;
+    let offset = (n as f32 * spacing) / 2.0;
+
+    commands.spawn((
+        Camera3d::default(),
+        Transform::from_xyz(0.0, offset, offset * 1.5).looking_at(Vec3::ZERO, Vec3::Y),
+        Msaa::Off,
+    ));
+
+    commands.spawn((
+        DirectionalLight {
+            illuminance: 3000.0,
+            shadow_maps_enabled: true,
+            ..default()
+        },
+        Transform::from_rotation(Quat::from_euler(
+            EulerRot::ZYX,
+            0.0,
+            1.0,
+            -std::f32::consts::FRAC_PI_4,
+        )),
+    ));
+
+    let shared_material = materials.add(StandardMaterial {
+        base_color: Color::WHITE,
+        ..default()
+    });
+
+    for x in 0..n {
+        for z in 0..n {
+            let material = if args.unique_materials {
+                materials.add(StandardMaterial {
+                    base_color: Color::srgb(x as f32 / n as f32, 0.5, z as f32 / n as f32),
+                    ..default()
+                })
+            } else {
+                shared_material.clone()
+            };
+
+            commands.spawn((
+                MeshletMesh3d(meshlet_handle.clone()),
+                MeshMaterial3d(material),
+                Transform::from_xyz(
+                    x as f32 * spacing - offset,
+                    0.0,
+                    z as f32 * spacing - offset,
+                ),
+            ));
+        }
+    }
+}