Meshlet new error projection (#15846)

* New error projection code taken from @zeux's meshoptimizer nanite.cpp
demo for determining LOD (thanks zeux!)
* Builder: `compute_lod_group_data()`
* Runtime: `lod_error_is_imperceptible()`

Cargo.toml

@@ -1213,7 +1213,7 @@ setup = [
     "curl",
     "-o",
     "assets/models/bunny.meshlet_mesh",
-    "https://raw.githubusercontent.com/JMS55/bevy_meshlet_asset/8443bbdee0bf517e6c297dede7f6a46ab712ee4c/bunny.meshlet_mesh",
+    "https://raw.githubusercontent.com/JMS55/bevy_meshlet_asset/167cdaf0b08f89fb747b83b94c27755f116cd408/bunny.meshlet_mesh",
   ],
 ]
 

crates/bevy_pbr/Cargo.toml

@@ -18,7 +18,7 @@ shader_format_glsl = ["bevy_render/shader_format_glsl"]
 trace = ["bevy_render/trace"]
 ios_simulator = ["bevy_render/ios_simulator"]
 # Enables the meshlet renderer for dense high-poly scenes (experimental)
-meshlet = ["dep:lz4_flex", "dep:range-alloc", "dep:bevy_tasks"]
+meshlet = ["dep:lz4_flex", "dep:range-alloc", "dep:half", "dep:bevy_tasks"]
 # Enables processing meshes into meshlet meshes
 meshlet_processor = [
   "meshlet",
@@ -50,16 +50,17 @@ bevy_window = { path = "../bevy_window", version = "0.15.0-dev" }
 # other
 bitflags = "2.3"
 fixedbitset = "0.5"
-# meshlet
-lz4_flex = { version = "0.11", default-features = false, features = [
-  "frame",
-], optional = true }
 derive_more = { version = "1", default-features = false, features = [
   "error",
   "from",
   "display",
 ] }
+# meshlet
+lz4_flex = { version = "0.11", default-features = false, features = [
+  "frame",
+], optional = true }
 range-alloc = { version = "0.1.3", optional = true }
+half = { version = "2", features = ["bytemuck"], optional = true }
 meshopt = { version = "0.3.0", optional = true }
 metis = { version = "0.2", optional = true }
 itertools = { version = "0.13", optional = true }

crates/bevy_pbr/src/meshlet/asset.rs

@@ -9,6 +9,7 @@ use bevy_reflect::TypePath;
 use bevy_tasks::block_on;
 use bytemuck::{Pod, Zeroable};
 use derive_more::derive::{Display, Error, From};
+use half::f16;
 use lz4_flex::frame::{FrameDecoder, FrameEncoder};
 use std::io::{Read, Write};
 
@@ -51,6 +52,8 @@ pub struct MeshletMesh {
     pub(crate) meshlets: Arc<[Meshlet]>,
     /// Spherical bounding volumes.
     pub(crate) meshlet_bounding_spheres: Arc<[MeshletBoundingSpheres]>,
+    /// Meshlet group and parent group simplification errors.
+    pub(crate) meshlet_simplification_errors: Arc<[MeshletSimplificationError]>,
 }
 
 /// A single meshlet within a [`MeshletMesh`].
@@ -90,12 +93,12 @@ pub struct Meshlet {
 #[derive(Copy, Clone, Pod, Zeroable)]
 #[repr(C)]
 pub struct MeshletBoundingSpheres {
-    /// The bounding sphere used for frustum and occlusion culling for this meshlet.
-    pub self_culling: MeshletBoundingSphere,
-    /// The bounding sphere used for determining if this meshlet is at the correct level of detail for a given view.
-    pub self_lod: MeshletBoundingSphere,
-    /// The bounding sphere used for determining if this meshlet's parent is at the correct level of detail for a given view.
-    pub parent_lod: MeshletBoundingSphere,
+    /// Bounding sphere used for frustum and occlusion culling for this meshlet.
+    pub culling_sphere: MeshletBoundingSphere,
+    /// Bounding sphere used for determining if this meshlet's group is at the correct level of detail for a given view.
+    pub lod_group_sphere: MeshletBoundingSphere,
+    /// Bounding sphere used for determining if this meshlet's parent group is at the correct level of detail for a given view.
+    pub lod_parent_group_sphere: MeshletBoundingSphere,
 }
 
 /// A spherical bounding volume used for a [`Meshlet`].
@@ -106,6 +109,16 @@ pub struct MeshletBoundingSphere {
     pub radius: f32,
 }
 
+/// Simplification error used for choosing level of detail for a [`Meshlet`].
+#[derive(Copy, Clone, Pod, Zeroable)]
+#[repr(C)]
+pub struct MeshletSimplificationError {
+    /// Simplification error used for determining if this meshlet's group is at the correct level of detail for a given view.
+    pub group_error: f16,
+    /// Simplification error used for determining if this meshlet's parent group is at the correct level of detail for a given view.
+    pub parent_group_error: f16,
+}
+
 /// An [`AssetSaver`] for `.meshlet_mesh` [`MeshletMesh`] assets.
 pub struct MeshletMeshSaver;
 
@@ -139,6 +152,7 @@ impl AssetSaver for MeshletMeshSaver {
         write_slice(&asset.indices, &mut writer)?;
         write_slice(&asset.meshlets, &mut writer)?;
         write_slice(&asset.meshlet_bounding_spheres, &mut writer)?;
+        write_slice(&asset.meshlet_simplification_errors, &mut writer)?;
         writer.finish()?;
 
         Ok(())
@@ -179,6 +193,7 @@ impl AssetLoader for MeshletMeshLoader {
         let indices = read_slice(reader)?;
         let meshlets = read_slice(reader)?;
         let meshlet_bounding_spheres = read_slice(reader)?;
+        let meshlet_simplification_errors = read_slice(reader)?;
 
         Ok(MeshletMesh {
             vertex_positions,
@@ -187,6 +202,7 @@ impl AssetLoader for MeshletMeshLoader {
             indices,
             meshlets,
             meshlet_bounding_spheres,
+            meshlet_simplification_errors,
         })
     }
 

crates/bevy_pbr/src/meshlet/cull_clusters.wgsl

@@ -1,6 +1,7 @@
 #import bevy_pbr::meshlet_bindings::{
     meshlet_cluster_meshlet_ids,
     meshlet_bounding_spheres,
+    meshlet_simplification_errors,
     meshlet_cluster_instance_ids,
     meshlet_instance_uniforms,
     meshlet_second_pass_candidates,
@@ -13,6 +14,7 @@
     meshlet_hardware_raster_indirect_args,
     meshlet_raster_clusters,
     meshlet_raster_cluster_rightmost_slot,
+    MeshletBoundingSphere,
 }
 #import bevy_render::maths::affine3_to_square
 
@@ -48,8 +50,8 @@ fn cull_clusters(
     let world_from_local = affine3_to_square(instance_uniform.world_from_local);
     let world_scale = max(length(world_from_local[0]), max(length(world_from_local[1]), length(world_from_local[2])));
     let bounding_spheres = meshlet_bounding_spheres[meshlet_id];
-    let culling_bounding_sphere_center = world_from_local * vec4(bounding_spheres.self_culling.center, 1.0);
-    let culling_bounding_sphere_radius = world_scale * bounding_spheres.self_culling.radius;
+    let culling_bounding_sphere_center = world_from_local * vec4(bounding_spheres.culling_sphere.center, 1.0);
+    let culling_bounding_sphere_radius = world_scale * bounding_spheres.culling_sphere.radius;
 
 #ifdef MESHLET_FIRST_CULLING_PASS
     // Frustum culling
@@ -60,19 +62,10 @@ fn cull_clusters(
         }
     }
 
-    // Calculate view-space LOD bounding sphere for the cluster
-    let lod_bounding_sphere_center = world_from_local * vec4(bounding_spheres.self_lod.center, 1.0);
-    let lod_bounding_sphere_radius = world_scale * bounding_spheres.self_lod.radius;
-    let lod_bounding_sphere_center_view_space = (view.view_from_world * vec4(lod_bounding_sphere_center.xyz, 1.0)).xyz;
-
-    // Calculate view-space LOD bounding sphere for the cluster's parent
-    let parent_lod_bounding_sphere_center = world_from_local * vec4(bounding_spheres.parent_lod.center, 1.0);
-    let parent_lod_bounding_sphere_radius = world_scale * bounding_spheres.parent_lod.radius;
-    let parent_lod_bounding_sphere_center_view_space = (view.view_from_world * vec4(parent_lod_bounding_sphere_center.xyz, 1.0)).xyz;
-
-    // Check LOD cut (cluster error imperceptible, and parent error not imperceptible)
-    let lod_is_ok = lod_error_is_imperceptible(lod_bounding_sphere_center_view_space, lod_bounding_sphere_radius);
-    let parent_lod_is_ok = lod_error_is_imperceptible(parent_lod_bounding_sphere_center_view_space, parent_lod_bounding_sphere_radius);
+    // Check LOD cut (cluster group error imperceptible, and parent group error not imperceptible)
+    let simplification_errors = unpack2x16float(meshlet_simplification_errors[meshlet_id]);
+    let lod_is_ok = lod_error_is_imperceptible(bounding_spheres.lod_group_sphere, simplification_errors.x, world_from_local, world_scale);
+    let parent_lod_is_ok = lod_error_is_imperceptible(bounding_spheres.lod_parent_group_sphere, simplification_errors.y, world_from_local, world_scale);
     if !lod_is_ok || parent_lod_is_ok { return; }
 #endif
 
@@ -80,8 +73,8 @@ fn cull_clusters(
 #ifdef MESHLET_FIRST_CULLING_PASS
     let previous_world_from_local = affine3_to_square(instance_uniform.previous_world_from_local);
     let previous_world_from_local_scale = max(length(previous_world_from_local[0]), max(length(previous_world_from_local[1]), length(previous_world_from_local[2])));
-    let occlusion_culling_bounding_sphere_center = previous_world_from_local * vec4(bounding_spheres.self_culling.center, 1.0);
-    let occlusion_culling_bounding_sphere_radius = previous_world_from_local_scale * bounding_spheres.self_culling.radius;
+    let occlusion_culling_bounding_sphere_center = previous_world_from_local * vec4(bounding_spheres.culling_sphere.center, 1.0);
+    let occlusion_culling_bounding_sphere_radius = previous_world_from_local_scale * bounding_spheres.culling_sphere.radius;
     let occlusion_culling_bounding_sphere_center_view_space = (previous_view.view_from_world * vec4(occlusion_culling_bounding_sphere_center.xyz, 1.0)).xyz;
 #else
     let occlusion_culling_bounding_sphere_center = culling_bounding_sphere_center;
@@ -148,14 +141,23 @@ fn cull_clusters(
     meshlet_raster_clusters[buffer_slot] = cluster_id;
 }
 
-// https://stackoverflow.com/questions/21648630/radius-of-projected-sphere-in-screen-space/21649403#21649403
-fn lod_error_is_imperceptible(cp: vec3<f32>, r: f32) -> bool {
-    let d2 = dot(cp, cp);
-    let r2 = r * r;
-    let sphere_diameter_uv = view.clip_from_view[0][0] * r / sqrt(d2 - r2);
-    let view_size = f32(max(view.viewport.z, view.viewport.w));
-    let sphere_diameter_pixels = sphere_diameter_uv * view_size;
-    return sphere_diameter_pixels < 1.0;
+// https://github.com/zeux/meshoptimizer/blob/1e48e96c7e8059321de492865165e9ef071bffba/demo/nanite.cpp#L115
+fn lod_error_is_imperceptible(lod_sphere: MeshletBoundingSphere, simplification_error: f32, world_from_local: mat4x4<f32>, world_scale: f32) -> bool {
+    let sphere_world_space = (world_from_local * vec4(lod_sphere.center, 1.0)).xyz;
+    let radius_world_space = world_scale * lod_sphere.radius;
+    let error_world_space = world_scale * simplification_error;
+
+    var projected_error = error_world_space;
+    if view.clip_from_view[3][3] != 1.0 {
+        // Perspective
+        let distance_to_closest_point_on_sphere = distance(sphere_world_space, view.world_position) - radius_world_space;
+        let distance_to_closest_point_on_sphere_clamped_to_znear = max(distance_to_closest_point_on_sphere, view.clip_from_view[3][2]);
+        projected_error /= distance_to_closest_point_on_sphere_clamped_to_znear;
+    }
+    projected_error *= view.clip_from_view[1][1] * 0.5;
+    projected_error *= view.viewport.w;
+
+    return projected_error < 1.0;
 }
 
 // https://zeux.io/2023/01/12/approximate-projected-bounds

crates/bevy_pbr/src/meshlet/from_mesh.rs

@@ -1,4 +1,6 @@
-use super::asset::{Meshlet, MeshletBoundingSphere, MeshletBoundingSpheres, MeshletMesh};
+use super::asset::{
+    Meshlet, MeshletBoundingSphere, MeshletBoundingSpheres, MeshletMesh, MeshletSimplificationError,
+};
 use alloc::borrow::Cow;
 use bevy_math::{ops::log2, IVec3, Vec2, Vec3, Vec3Swizzles};
 use bevy_render::{
@@ -7,13 +9,12 @@ use bevy_render::{
 };
 use bevy_utils::HashMap;
 use bitvec::{order::Lsb0, vec::BitVec, view::BitView};
-use core::ops::Range;
+use core::{iter, ops::Range};
 use derive_more::derive::{Display, Error};
+use half::f16;
 use itertools::Itertools;
 use meshopt::{
-    build_meshlets, compute_cluster_bounds, compute_meshlet_bounds,
-    ffi::{meshopt_Bounds, meshopt_Meshlet},
-    simplify, Meshlets, SimplifyOptions, VertexDataAdapter,
+    build_meshlets, ffi::meshopt_Meshlet, simplify, Meshlets, SimplifyOptions, VertexDataAdapter,
 };
 use metis::Graph;
 use smallvec::SmallVec;
@@ -69,19 +70,21 @@ impl MeshletMesh {
         let mut bounding_spheres = meshlets
             .iter()
             .map(|meshlet| compute_meshlet_bounds(meshlet, &vertices))
-            .map(convert_meshlet_bounds)
             .map(|bounding_sphere| MeshletBoundingSpheres {
-                self_culling: bounding_sphere,
-                self_lod: MeshletBoundingSphere {
-                    center: bounding_sphere.center,
+                culling_sphere: bounding_sphere,
+                lod_group_sphere: bounding_sphere,
+                lod_parent_group_sphere: MeshletBoundingSphere {
+                    center: Vec3::ZERO,
                     radius: 0.0,
                 },
-                parent_lod: MeshletBoundingSphere {
-                    center: bounding_sphere.center,
-                    radius: f32::MAX,
-                },
             })
             .collect::<Vec<_>>();
+        let mut simplification_errors = iter::repeat(MeshletSimplificationError {
+            group_error: f16::ZERO,
+            parent_group_error: f16::MAX,
+        })
+        .take(meshlets.len())
+        .collect::<Vec<_>>();
 
         // Build further LODs
         let mut simplification_queue = 0..meshlets.len();
@@ -107,22 +110,13 @@ impl MeshletMesh {
                     continue;
                 };
 
-                // Force parent error to be >= child error (we're currently building the parent from its children)
-                group_error = group_meshlets.iter().fold(group_error, |acc, meshlet_id| {
-                    acc.max(bounding_spheres[*meshlet_id].self_lod.radius)
-                });
-
-                // Build a new LOD bounding sphere for the simplified group as a whole
-                let mut group_bounding_sphere = convert_meshlet_bounds(compute_cluster_bounds(
-                    &simplified_group_indices,
-                    &vertices,
-                ));
-                group_bounding_sphere.radius = group_error;
-
-                // For each meshlet in the group set their parent LOD bounding sphere to that of the simplified group
-                for meshlet_id in group_meshlets {
-                    bounding_spheres[meshlet_id].parent_lod = group_bounding_sphere;
-                }
+                // Compute LOD data for the group
+                let group_bounding_sphere = compute_lod_group_data(
+                    &group_meshlets,
+                    &mut group_error,
+                    &mut bounding_spheres,
+                    &mut simplification_errors,
+                );
 
                 // Build new meshlets using the simplified group
                 let new_meshlets_count = split_simplified_group_into_new_meshlets(
@@ -131,22 +125,24 @@ impl MeshletMesh {
                     &mut meshlets,
                 );
 
-                // Calculate the culling bounding sphere for the new meshlets and set their LOD bounding spheres
+                // Calculate the culling bounding sphere for the new meshlets and set their LOD group data
                 let new_meshlet_ids = (meshlets.len() - new_meshlets_count)..meshlets.len();
-                bounding_spheres.extend(
-                    new_meshlet_ids
-                        .map(|meshlet_id| {
-                            compute_meshlet_bounds(meshlets.get(meshlet_id), &vertices)
-                        })
-                        .map(convert_meshlet_bounds)
-                        .map(|bounding_sphere| MeshletBoundingSpheres {
-                            self_culling: bounding_sphere,
-                            self_lod: group_bounding_sphere,
-                            parent_lod: MeshletBoundingSphere {
-                                center: group_bounding_sphere.center,
-                                radius: f32::MAX,
+                bounding_spheres.extend(new_meshlet_ids.clone().map(|meshlet_id| {
+                    MeshletBoundingSpheres {
+                        culling_sphere: compute_meshlet_bounds(meshlets.get(meshlet_id), &vertices),
+                        lod_group_sphere: group_bounding_sphere,
+                        lod_parent_group_sphere: MeshletBoundingSphere {
+                            center: Vec3::ZERO,
+                            radius: 0.0,
                         },
-                        }),
+                    }
+                }));
+                simplification_errors.extend(
+                    iter::repeat(MeshletSimplificationError {
+                        group_error,
+                        parent_group_error: f16::MAX,
+                    })
+                    .take(new_meshlet_ids.len()),
                 );
             }
 
@@ -179,6 +175,7 @@ impl MeshletMesh {
             indices: meshlets.triangles.into(),
             meshlets: bevy_meshlets.into(),
             meshlet_bounding_spheres: bounding_spheres.into(),
+            meshlet_simplification_errors: simplification_errors.into(),
         })
     }
 }
@@ -303,7 +300,7 @@ fn simplify_meshlet_group(
     group_meshlets: &[usize],
     meshlets: &Meshlets,
     vertices: &VertexDataAdapter<'_>,
-) -> Option<(Vec<u32>, f32)> {
+) -> Option<(Vec<u32>, f16)> {
     // Build a new index buffer into the mesh vertex data by combining all meshlet data in the group
     let mut group_indices = Vec::new();
     for meshlet_id in group_meshlets {
@@ -330,10 +327,55 @@ fn simplify_meshlet_group(
         return None;
     }
 
-    // Convert error from diameter to radius
-    error *= 0.5;
+    Some((simplified_group_indices, f16::from_f32(error)))
+}
 
-    Some((simplified_group_indices, error))
+fn compute_lod_group_data(
+    group_meshlets: &[usize],
+    group_error: &mut f16,
+    bounding_spheres: &mut [MeshletBoundingSpheres],
+    simplification_errors: &mut [MeshletSimplificationError],
+) -> MeshletBoundingSphere {
+    let mut group_bounding_sphere = MeshletBoundingSphere {
+        center: Vec3::ZERO,
+        radius: 0.0,
+    };
+
+    // Compute the lod group sphere center as a weighted average of the children spheres
+    let mut weight = 0.0;
+    for meshlet_id in group_meshlets {
+        let meshlet_lod_bounding_sphere = bounding_spheres[*meshlet_id].lod_group_sphere;
+        group_bounding_sphere.center +=
+            meshlet_lod_bounding_sphere.center * meshlet_lod_bounding_sphere.radius;
+        weight += meshlet_lod_bounding_sphere.radius;
+    }
+    group_bounding_sphere.center /= weight;
+
+    // Force parent group sphere to contain all child group spheres (we're currently building the parent from its children)
+    // TODO: This does not produce the absolute minimal bounding sphere. Doing so is non-trivial.
+    //       "Smallest enclosing balls of balls" http://www.inf.ethz.ch/personal/emo/DoctThesisFiles/fischer05.pdf
+    for meshlet_id in group_meshlets {
+        let meshlet_lod_bounding_sphere = bounding_spheres[*meshlet_id].lod_group_sphere;
+        let d = meshlet_lod_bounding_sphere
+            .center
+            .distance(group_bounding_sphere.center);
+        group_bounding_sphere.radius = group_bounding_sphere
+            .radius
+            .max(meshlet_lod_bounding_sphere.radius + d);
+    }
+
+    // Force parent error to be >= child error (we're currently building the parent from its children)
+    for meshlet_id in group_meshlets {
+        *group_error = group_error.max(simplification_errors[*meshlet_id].group_error);
+    }
+
+    // Set the children's lod parent group data to the new lod group we just made
+    for meshlet_id in group_meshlets {
+        bounding_spheres[*meshlet_id].lod_parent_group_sphere = group_bounding_sphere;
+        simplification_errors[*meshlet_id].parent_group_error = *group_error;
+    }
+
+    group_bounding_sphere
 }
 
 fn split_simplified_group_into_new_meshlets(
@@ -449,7 +491,11 @@ fn build_and_compress_meshlet_vertex_data(
     });
 }
 
-fn convert_meshlet_bounds(bounds: meshopt_Bounds) -> MeshletBoundingSphere {
+fn compute_meshlet_bounds(
+    meshlet: meshopt::Meshlet<'_>,
+    vertices: &VertexDataAdapter<'_>,
+) -> MeshletBoundingSphere {
+    let bounds = meshopt::compute_meshlet_bounds(meshlet, vertices);
     MeshletBoundingSphere {
         center: bounds.center.into(),
         radius: bounds.radius,

crates/bevy_pbr/src/meshlet/meshlet_bindings.wgsl

@@ -25,9 +25,9 @@ fn get_meshlet_triangle_count(meshlet: ptr<function, Meshlet>) -> u32 {
 }
 
 struct MeshletBoundingSpheres {
-    self_culling: MeshletBoundingSphere,
-    self_lod: MeshletBoundingSphere,
-    parent_lod: MeshletBoundingSphere,
+    culling_sphere: MeshletBoundingSphere,
+    lod_group_sphere: MeshletBoundingSphere,
+    lod_parent_group_sphere: MeshletBoundingSphere,
 }
 
 struct MeshletBoundingSphere {
@@ -62,16 +62,17 @@ var<push_constant> cluster_count: u32;
 var<push_constant> meshlet_raster_cluster_rightmost_slot: u32;
 @group(0) @binding(0) var<storage, read> meshlet_cluster_meshlet_ids: array<u32>; // Per cluster
 @group(0) @binding(1) var<storage, read> meshlet_bounding_spheres: array<MeshletBoundingSpheres>; // Per meshlet
-@group(0) @binding(2) var<storage, read> meshlet_cluster_instance_ids: array<u32>; // Per cluster
-@group(0) @binding(3) var<storage, read> meshlet_instance_uniforms: array<Mesh>; // Per entity instance
-@group(0) @binding(4) var<storage, read> meshlet_view_instance_visibility: array<u32>; // 1 bit per entity instance, packed as a bitmask
-@group(0) @binding(5) var<storage, read_write> meshlet_second_pass_candidates: array<atomic<u32>>; // 1 bit per cluster , packed as a bitmask
-@group(0) @binding(6) var<storage, read_write> meshlet_software_raster_indirect_args: DispatchIndirectArgs; // Single object shared between all workgroups/clusters/triangles
-@group(0) @binding(7) var<storage, read_write> meshlet_hardware_raster_indirect_args: DrawIndirectArgs; // Single object shared between all workgroups/clusters/triangles
-@group(0) @binding(8) var<storage, read_write> meshlet_raster_clusters: array<u32>; // Single object shared between all workgroups/clusters/triangles
-@group(0) @binding(9) var depth_pyramid: texture_2d<f32>; // From the end of the last frame for the first culling pass, and from the first raster pass for the second culling pass
-@group(0) @binding(10) var<uniform> view: View;
-@group(0) @binding(11) var<uniform> previous_view: PreviousViewUniforms;
+@group(0) @binding(2) var<storage, read> meshlet_simplification_errors: array<u32>; // Per meshlet
+@group(0) @binding(3) var<storage, read> meshlet_cluster_instance_ids: array<u32>; // Per cluster
+@group(0) @binding(4) var<storage, read> meshlet_instance_uniforms: array<Mesh>; // Per entity instance
+@group(0) @binding(5) var<storage, read> meshlet_view_instance_visibility: array<u32>; // 1 bit per entity instance, packed as a bitmask
+@group(0) @binding(6) var<storage, read_write> meshlet_second_pass_candidates: array<atomic<u32>>; // 1 bit per cluster , packed as a bitmask
+@group(0) @binding(7) var<storage, read_write> meshlet_software_raster_indirect_args: DispatchIndirectArgs; // Single object shared between all workgroups/clusters/triangles
+@group(0) @binding(8) var<storage, read_write> meshlet_hardware_raster_indirect_args: DrawIndirectArgs; // Single object shared between all workgroups/clusters/triangles
+@group(0) @binding(9) var<storage, read_write> meshlet_raster_clusters: array<u32>; // Single object shared between all workgroups/clusters/triangles
+@group(0) @binding(10) var depth_pyramid: texture_2d<f32>; // From the end of the last frame for the first culling pass, and from the first raster pass for the second culling pass
+@group(0) @binding(11) var<uniform> view: View;
+@group(0) @binding(12) var<uniform> previous_view: PreviousViewUniforms;
 
 fn should_cull_instance(instance_id: u32) -> bool {
     let bit_offset = instance_id % 32u;

crates/bevy_pbr/src/meshlet/meshlet_mesh_manager.rs

@@ -1,5 +1,5 @@
 use super::{
-    asset::{Meshlet, MeshletBoundingSpheres},
+    asset::{Meshlet, MeshletBoundingSpheres, MeshletSimplificationError},
     persistent_buffer::PersistentGpuBuffer,
     MeshletMesh,
 };
@@ -26,7 +26,8 @@ pub struct MeshletMeshManager {
     pub indices: PersistentGpuBuffer<Arc<[u8]>>,
     pub meshlets: PersistentGpuBuffer<Arc<[Meshlet]>>,
     pub meshlet_bounding_spheres: PersistentGpuBuffer<Arc<[MeshletBoundingSpheres]>>,
-    meshlet_mesh_slices: HashMap<AssetId<MeshletMesh>, [Range<BufferAddress>; 6]>,
+    pub meshlet_simplification_errors: PersistentGpuBuffer<Arc<[MeshletSimplificationError]>>,
+    meshlet_mesh_slices: HashMap<AssetId<MeshletMesh>, [Range<BufferAddress>; 7]>,
 }
 
 impl FromWorld for MeshletMeshManager {
@@ -42,6 +43,10 @@ impl FromWorld for MeshletMeshManager {
                 "meshlet_bounding_spheres",
                 render_device,
             ),
+            meshlet_simplification_errors: PersistentGpuBuffer::new(
+                "meshlet_simplification_errors",
+                render_device,
+            ),
             meshlet_mesh_slices: HashMap::new(),
         }
     }
@@ -81,6 +86,9 @@ impl MeshletMeshManager {
             let meshlet_bounding_spheres_slice = self
                 .meshlet_bounding_spheres
                 .queue_write(Arc::clone(&meshlet_mesh.meshlet_bounding_spheres), ());
+            let meshlet_simplification_errors_slice = self
+                .meshlet_simplification_errors
+                .queue_write(Arc::clone(&meshlet_mesh.meshlet_simplification_errors), ());
 
             [
                 vertex_positions_slice,
@@ -89,11 +97,12 @@ impl MeshletMeshManager {
                 indices_slice,
                 meshlets_slice,
                 meshlet_bounding_spheres_slice,
+                meshlet_simplification_errors_slice,
             ]
         };
 
         // If the MeshletMesh asset has not been uploaded to the GPU yet, queue it for uploading
-        let [_, _, _, _, meshlets_slice, _] = self
+        let [_, _, _, _, meshlets_slice, _, _] = self
             .meshlet_mesh_slices
             .entry(asset_id)
             .or_insert_with_key(queue_meshlet_mesh)
@@ -106,7 +115,7 @@ impl MeshletMeshManager {
 
     pub fn remove(&mut self, asset_id: &AssetId<MeshletMesh>) {
         if let Some(
-            [vertex_positions_slice, vertex_normals_slice, vertex_uvs_slice, indices_slice, meshlets_slice, meshlet_bounding_spheres_slice],
+            [vertex_positions_slice, vertex_normals_slice, vertex_uvs_slice, indices_slice, meshlets_slice, meshlet_bounding_spheres_slice, meshlet_simplification_errors_slice],
         ) = self.meshlet_mesh_slices.remove(asset_id)
         {
             self.vertex_positions
@@ -117,6 +126,8 @@ impl MeshletMeshManager {
             self.meshlets.mark_slice_unused(meshlets_slice);
             self.meshlet_bounding_spheres
                 .mark_slice_unused(meshlet_bounding_spheres_slice);
+            self.meshlet_simplification_errors
+                .mark_slice_unused(meshlet_simplification_errors_slice);
         }
     }
 }
@@ -145,4 +156,7 @@ pub fn perform_pending_meshlet_mesh_writes(
     meshlet_mesh_manager
         .meshlet_bounding_spheres
         .perform_writes(&render_queue, &render_device);
+    meshlet_mesh_manager
+        .meshlet_simplification_errors
+        .perform_writes(&render_queue, &render_device);
 }

crates/bevy_pbr/src/meshlet/mod.rs

@@ -290,6 +290,7 @@ impl Plugin for MeshletPlugin {
     }
 }
 
+/// The meshlet mesh equivalent of [`bevy_render::mesh::Mesh3d`].
 #[derive(Component, Clone, Debug, Default, Deref, DerefMut, Reflect, PartialEq, Eq, From)]
 #[reflect(Component, Default)]
 #[require(Transform, Visibility)]

crates/bevy_pbr/src/meshlet/persistent_buffer_impls.rs

@@ -1,10 +1,42 @@
 use super::{
-    asset::{Meshlet, MeshletBoundingSpheres},
+    asset::{Meshlet, MeshletBoundingSpheres, MeshletSimplificationError},
     persistent_buffer::PersistentGpuBufferable,
 };
 use alloc::sync::Arc;
 use bevy_math::Vec2;
 
+impl PersistentGpuBufferable for Arc<[Meshlet]> {
+    type Metadata = (u64, u64, u64);
+
+    fn size_in_bytes(&self) -> usize {
+        self.len() * size_of::<Meshlet>()
+    }
+
+    fn write_bytes_le(
+        &self,
+        (vertex_position_offset, vertex_attribute_offset, index_offset): Self::Metadata,
+        buffer_slice: &mut [u8],
+    ) {
+        let vertex_position_offset = (vertex_position_offset * 8) as u32;
+        let vertex_attribute_offset = (vertex_attribute_offset as usize / size_of::<u32>()) as u32;
+        let index_offset = index_offset as u32;
+
+        for (i, meshlet) in self.iter().enumerate() {
+            let size = size_of::<Meshlet>();
+            let i = i * size;
+            let bytes = bytemuck::cast::<_, [u8; size_of::<Meshlet>()]>(Meshlet {
+                start_vertex_position_bit: meshlet.start_vertex_position_bit
+                    + vertex_position_offset,
+                start_vertex_attribute_id: meshlet.start_vertex_attribute_id
+                    + vertex_attribute_offset,
+                start_index_id: meshlet.start_index_id + index_offset,
+                ..*meshlet
+            });
+            buffer_slice[i..(i + size)].clone_from_slice(&bytes);
+        }
+    }
+}
+
 impl PersistentGpuBufferable for Arc<[u8]> {
     type Metadata = ();
 
@@ -41,38 +73,6 @@ impl PersistentGpuBufferable for Arc<[Vec2]> {
     }
 }
 
-impl PersistentGpuBufferable for Arc<[Meshlet]> {
-    type Metadata = (u64, u64, u64);
-
-    fn size_in_bytes(&self) -> usize {
-        self.len() * size_of::<Meshlet>()
-    }
-
-    fn write_bytes_le(
-        &self,
-        (vertex_position_offset, vertex_attribute_offset, index_offset): Self::Metadata,
-        buffer_slice: &mut [u8],
-    ) {
-        let vertex_position_offset = (vertex_position_offset * 8) as u32;
-        let vertex_attribute_offset = (vertex_attribute_offset as usize / size_of::<u32>()) as u32;
-        let index_offset = index_offset as u32;
-
-        for (i, meshlet) in self.iter().enumerate() {
-            let size = size_of::<Meshlet>();
-            let i = i * size;
-            let bytes = bytemuck::cast::<_, [u8; size_of::<Meshlet>()]>(Meshlet {
-                start_vertex_position_bit: meshlet.start_vertex_position_bit
-                    + vertex_position_offset,
-                start_vertex_attribute_id: meshlet.start_vertex_attribute_id
-                    + vertex_attribute_offset,
-                start_index_id: meshlet.start_index_id + index_offset,
-                ..*meshlet
-            });
-            buffer_slice[i..(i + size)].clone_from_slice(&bytes);
-        }
-    }
-}
-
 impl PersistentGpuBufferable for Arc<[MeshletBoundingSpheres]> {
     type Metadata = ();
 
@@ -84,3 +84,15 @@ impl PersistentGpuBufferable for Arc<[MeshletBoundingSpheres]> {
         buffer_slice.clone_from_slice(bytemuck::cast_slice(self));
     }
 }
+
+impl PersistentGpuBufferable for Arc<[MeshletSimplificationError]> {
+    type Metadata = ();
+
+    fn size_in_bytes(&self) -> usize {
+        self.len() * size_of::<MeshletSimplificationError>()
+    }
+
+    fn write_bytes_le(&self, _: Self::Metadata, buffer_slice: &mut [u8]) {
+        buffer_slice.clone_from_slice(bytemuck::cast_slice(self));
+    }
+}

crates/bevy_pbr/src/meshlet/resource_manager.rs

@@ -135,6 +135,7 @@ impl ResourceManager {
                         storage_buffer_read_only_sized(false, None),
                         storage_buffer_read_only_sized(false, None),
                         storage_buffer_read_only_sized(false, None),
+                        storage_buffer_read_only_sized(false, None),
                         storage_buffer_sized(false, None),
                         storage_buffer_sized(false, None),
                         storage_buffer_sized(false, None),
@@ -624,6 +625,7 @@ pub fn prepare_meshlet_view_bind_groups(
         let entries = BindGroupEntries::sequential((
             cluster_meshlet_ids.as_entire_binding(),
             meshlet_mesh_manager.meshlet_bounding_spheres.binding(),
+            meshlet_mesh_manager.meshlet_simplification_errors.binding(),
             cluster_instance_ids.as_entire_binding(),
             instance_manager.instance_uniforms.binding().unwrap(),
             view_resources.instance_visibility.as_entire_binding(),
@@ -652,6 +654,7 @@ pub fn prepare_meshlet_view_bind_groups(
         let entries = BindGroupEntries::sequential((
             cluster_meshlet_ids.as_entire_binding(),
             meshlet_mesh_manager.meshlet_bounding_spheres.binding(),
+            meshlet_mesh_manager.meshlet_simplification_errors.binding(),
             cluster_instance_ids.as_entire_binding(),
             instance_manager.instance_uniforms.binding().unwrap(),
             view_resources.instance_visibility.as_entire_binding(),

examples/3d/meshlet.rs

@@ -17,7 +17,7 @@ use camera_controller::{CameraController, CameraControllerPlugin};
 use std::{f32::consts::PI, path::Path, process::ExitCode};
 
 const ASSET_URL: &str =
-    "https://raw.githubusercontent.com/JMS55/bevy_meshlet_asset/8443bbdee0bf517e6c297dede7f6a46ab712ee4c/bunny.meshlet_mesh";
+    "https://raw.githubusercontent.com/JMS55/bevy_meshlet_asset/167cdaf0b08f89fb747b83b94c27755f116cd408/bunny.meshlet_mesh";
 
 fn main() -> ExitCode {
     if !Path::new("./assets/models/bunny.meshlet_mesh").exists() {