Mesh Skinning. Attempt #3 (#4238)

# Objective
Load skeletal weights and indices from GLTF files. Animate meshes.

## Solution
 - Load skeletal weights and indices from GLTF files.
 - Added `SkinnedMesh` component and ` SkinnedMeshInverseBindPose` asset
 - Added `extract_skinned_meshes` to extract joint matrices.
 - Added queue phase systems for enqueuing the buffer writes.

Some notes:

 -  This ports part of # #2359 to the current main.
 -  This generates new `BufferVec`s and bind groups every frame. The expectation here is that the number of `Query::get` calls during extract is probably going to be the stronger bottleneck, with up to 256 calls per skinned mesh. Until that is optimized, caching buffers and bind groups is probably a non-concern.
 - Unfortunately, due to the uniform size requirements, this means a 16KB buffer is allocated for every skinned mesh every frame. There's probably a few ways to get around this, but most of them require either compute shaders or storage buffers, which are both incompatible with WebGL2.

Co-authored-by: james7132 <contact@jamessliu.com>
Co-authored-by: François <mockersf@gmail.com>
Co-authored-by: James Liu <contact@jamessliu.com>

Cargo.toml

@@ -235,6 +235,15 @@ path = "examples/3d/update_gltf_scene.rs"
 name = "wireframe"
 path = "examples/3d/wireframe.rs"
 
+# Animation
+[[example]]
+name = "custom_skinned_mesh"
+path = "examples/animation/custom_skinned_mesh.rs"
+
+[[example]]
+name = "gltf_skinned_mesh"
+path = "examples/animation/gltf_skinned_mesh.rs"
+
 # Application
 [[example]]
 name = "custom_loop"

assets/models/SimpleSkin/SimpleSkin.gltf

@@ -0,0 +1 @@
+{"scenes":[{"nodes":[0]}],"nodes":[{"skin":0,"mesh":0,"children":[1]},{"children":[2],"translation":[0,1,0]},{"rotation":[0,0,0,1]}],"meshes":[{"primitives":[{"attributes":{"POSITION":1,"JOINTS_0":2,"WEIGHTS_0":3},"indices":0}]}],"skins":[{"inverseBindMatrices":4,"joints":[1,2]}],"animations":[{"channels":[{"sampler":0,"target":{"node":2,"path":"rotation"}}],"samplers":[{"input":5,"interpolation":"LINEAR","output":6}]}],"buffers":[{"uri":"data:application/gltf-buffer;base64,AAABAAMAAAADAAIAAgADAAUAAgAFAAQABAAFAAcABAAHAAYABgAHAAkABgAJAAgAAAAAAAAAAAAAAAAAAACAPwAAAAAAAAAAAAAAAAAAAD8AAAAAAACAPwAAAD8AAAAAAAAAAAAAgD8AAAAAAACAPwAAgD8AAAAAAAAAAAAAwD8AAAAAAACAPwAAwD8AAAAAAAAAAAAAAEAAAAAAAACAPwAAAEAAAAAA","byteLength":168},{"uri":"data:application/gltf-buffer;base64,AAABAAAAAAAAAAAAAAAAAAAAAQAAAAAAAAAAAAAAAAAAAAEAAAAAAAAAAAAAAAAAAAABAAAAAAAAAAAAAAAAAAAAAQAAAAAAAAAAAAAAAAAAAAEAAAAAAAAAAAAAAAAAAAABAAAAAAAAAAAAAAAAAAAAAQAAAAAAAAAAAAAAAAAAAAEAAAAAAAAAAAAAAAAAAAABAAAAAAAAAAAAAAAAAAAAgD8AAAAAAAAAAAAAAAAAAIA/AAAAAAAAAAAAAAAAAABAPwAAgD4AAAAAAAAAAAAAQD8AAIA+AAAAAAAAAAAAAAA/AAAAPwAAAAAAAAAAAAAAPwAAAD8AAAAAAAAAAAAAgD4AAEA/AAAAAAAAAAAAAIA+AABAPwAAAAAAAAAAAAAAAAAAgD8AAAAAAAAAAAAAAAAAAIA/AAAAAAAAAAA=","byteLength":320},{"uri":"data:application/gltf-buffer;base64,AACAPwAAAAAAAAAAAAAAAAAAAAAAAIA/AAAAAAAAAAAAAAAAAAAAAAAAgD8AAAAAAAAAvwAAgL8AAAAAAACAPwAAgD8AAAAAAAAAAAAAAAAAAAAAAACAPwAAAAAAAAAAAAAAAAAAAAAAAIA/AAAAAAAAAL8AAIC/AAAAAAAAgD8=","byteLength":128},{"uri":"data:application/gltf-buffer;base64,AAAAAAAAAD8AAIA/AADAPwAAAEAAACBAAABAQAAAYEAAAIBAAACQQAAAoEAAALBAAAAAAAAAAAAAAAAAAACAPwAAAAAAAAAAkxjEPkSLbD8AAAAAAAAAAPT9ND/0/TQ/AAAAAAAAAAD0/TQ/9P00PwAAAAAAAAAAkxjEPkSLbD8AAAAAAAAAAAAAAAAAAIA/AAAAAAAAAAAAAAAAAACAPwAAAAAAAAAAkxjEvkSLbD8AAAAAAAAAAPT9NL/0/TQ/AAAAAAAAAAD0/TS/9P00PwAAAAAAAAAAkxjEvkSLbD8AAAAAAAAAAAAAAAAAAIA/","byteLength":240}],"bufferViews":[{"buffer":0,"byteOffset":0,"byteLength":48,"target":34963},{"buffer":0,"byteOffset":48,"byteLength":120,"target":34962},{"buffer":1,"byteOffset":0,"byteLength":320,"byteStride":16},{"buffer":2,"byteOffset":0,"byteLength":128},{"buffer":3,"byteOffset":0,"byteLength":240}],"accessors":[{"bufferView":0,"byteOffset":0,"componentType":5123,"count":24,"type":"SCALAR","max":[9],"min":[0]},{"bufferView":1,"byteOffset":0,"componentType":5126,"count":10,"type":"VEC3","max":[1,2,0],"min":[0,0,0]},{"bufferView":2,"byteOffset":0,"componentType":5123,"count":10,"type":"VEC4","max":[0,1,0,0],"min":[0,1,0,0]},{"bufferView":2,"byteOffset":160,"componentType":5126,"count":10,"type":"VEC4","max":[1,1,0,0],"min":[0,0,0,0]},{"bufferView":3,"byteOffset":0,"componentType":5126,"count":2,"type":"MAT4","max":[1,0,0,0,0,1,0,0,0,0,1,0,-0.5,-1,0,1],"min":[1,0,0,0,0,1,0,0,0,0,1,0,-0.5,-1,0,1]},{"bufferView":4,"byteOffset":0,"componentType":5126,"count":12,"type":"SCALAR","max":[5.5],"min":[0]},{"bufferView":4,"byteOffset":48,"componentType":5126,"count":12,"type":"VEC4","max":[0,0,0.707,1],"min":[0,0,-0.707,0.707]}],"asset":{"version":"2.0"}}

crates/bevy_gltf/src/loader.rs

@@ -3,7 +3,7 @@ use bevy_asset::{
     AssetIoError, AssetLoader, AssetPath, BoxedFuture, Handle, LoadContext, LoadedAsset,
 };
 use bevy_core::Name;
-use bevy_ecs::{prelude::FromWorld, world::World};
+use bevy_ecs::{entity::Entity, prelude::FromWorld, world::World};
 use bevy_hierarchy::{BuildWorldChildren, WorldChildBuilder};
 use bevy_log::warn;
 use bevy_math::{Mat4, Quat, Vec3};
@@ -16,7 +16,10 @@ use bevy_render::{
         Camera, Camera2d, Camera3d, CameraProjection, OrthographicProjection, PerspectiveProjection,
     },
     color::Color,
-    mesh::{Indices, Mesh, VertexAttributeValues},
+    mesh::{
+        skinning::{SkinnedMesh, SkinnedMeshInverseBindposes},
+        Indices, Mesh, VertexAttributeValues,
+    },
     primitives::{Aabb, Frustum},
     render_resource::{AddressMode, Face, FilterMode, PrimitiveTopology, SamplerDescriptor},
     renderer::RenderDevice,
@@ -249,6 +252,18 @@ async fn load_gltf<'a, 'b>(
             //     mesh.insert_attribute(Mesh::ATTRIBUTE_COLOR, vertex_attribute);
             // }
 
+            if let Some(iter) = reader.read_joints(0) {
+                let vertex_attribute = VertexAttributeValues::Uint16x4(iter.into_u16().collect());
+                mesh.insert_attribute(Mesh::ATTRIBUTE_JOINT_INDEX, vertex_attribute);
+            }
+
+            if let Some(vertex_attribute) = reader
+                .read_weights(0)
+                .map(|v| VertexAttributeValues::Float32x4(v.into_f32().collect()))
+            {
+                mesh.insert_attribute(Mesh::ATTRIBUTE_JOINT_WEIGHT, vertex_attribute);
+            }
+
             if let Some(indices) = reader.read_indices() {
                 mesh.set_indices(Some(Indices::U32(indices.into_u32().collect())));
             };
@@ -384,18 +399,45 @@ async fn load_gltf<'a, 'b>(
             });
     }
 
+    let skinned_mesh_inverse_bindposes: Vec<_> = gltf
+        .skins()
+        .map(|gltf_skin| {
+            let reader = gltf_skin.reader(|buffer| Some(&buffer_data[buffer.index()]));
+            let inverse_bindposes: Vec<Mat4> = reader
+                .read_inverse_bind_matrices()
+                .unwrap()
+                .map(|mat| Mat4::from_cols_array_2d(&mat))
+                .collect();
+
+            load_context.set_labeled_asset(
+                &skin_label(&gltf_skin),
+                LoadedAsset::new(SkinnedMeshInverseBindposes::from(inverse_bindposes)),
+            )
+        })
+        .collect();
+
     let mut scenes = vec![];
     let mut named_scenes = HashMap::default();
     for scene in gltf.scenes() {
         let mut err = None;
         let mut world = World::default();
+        let mut node_index_to_entity_map = HashMap::new();
+        let mut entity_to_skin_index_map = HashMap::new();
+
         world
             .spawn()
             .insert_bundle(TransformBundle::identity())
             .with_children(|parent| {
                 for node in scene.nodes() {
-                    let result =
+                    let result = load_node(
-                        load_node(&node, parent, load_context, &buffer_data, &animated_nodes);
+                        &node,
+                        parent,
+                        load_context,
+                        &buffer_data,
+                        &animated_nodes,
+                        &mut node_index_to_entity_map,
+                        &mut entity_to_skin_index_map,
+                    );
                     if result.is_err() {
                         err = Some(result);
                         return;
@@ -405,6 +447,21 @@ async fn load_gltf<'a, 'b>(
         if let Some(Err(err)) = err {
             return Err(err);
         }
+
+        for (&entity, &skin_index) in &entity_to_skin_index_map {
+            let mut entity = world.entity_mut(entity);
+            let skin = gltf.skins().nth(skin_index).unwrap();
+            let joint_entities: Vec<_> = skin
+                .joints()
+                .map(|node| node_index_to_entity_map[&node.index()])
+                .collect();
+
+            entity.insert(SkinnedMesh {
+                inverse_bindposes: skinned_mesh_inverse_bindposes[skin_index].clone(),
+                joints: joint_entities,
+            });
+        }
+
         let scene_handle = load_context
             .set_labeled_asset(&scene_label(&scene), LoadedAsset::new(Scene::new(world)));
 
@@ -575,6 +632,8 @@ fn load_node(
     load_context: &mut LoadContext,
     buffer_data: &[Vec<u8>],
     animated_nodes: &HashSet<usize>,
+    node_index_to_entity_map: &mut HashMap<usize, Entity>,
+    entity_to_skin_index_map: &mut HashMap<Entity, usize>,
 ) -> Result<(), GltfError> {
     let transform = gltf_node.transform();
     let mut gltf_error = None;
@@ -645,6 +704,9 @@ fn load_node(
         }
     }
 
+    // Map node index to entity
+    node_index_to_entity_map.insert(gltf_node.index(), node.id());
+
     node.with_children(|parent| {
         if let Some(mesh) = gltf_node.mesh() {
             // append primitives
@@ -660,13 +722,13 @@ fn load_node(
                 }
 
                 let primitive_label = primitive_label(&mesh, &primitive);
+                let bounds = primitive.bounding_box();
                 let mesh_asset_path =
                     AssetPath::new_ref(load_context.path(), Some(&primitive_label));
                 let material_asset_path =
                     AssetPath::new_ref(load_context.path(), Some(&material_label));
 
-                let bounds = primitive.bounding_box();
+                let node = parent
-                parent
                     .spawn_bundle(PbrBundle {
                         mesh: load_context.get_handle(mesh_asset_path),
                         material: load_context.get_handle(material_asset_path),
@@ -675,7 +737,13 @@ fn load_node(
                     .insert(Aabb::from_min_max(
                         Vec3::from_slice(&bounds.min),
                         Vec3::from_slice(&bounds.max),
-                    ));
+                    ))
+                    .id();
+
+                // Mark for adding skinned mesh
+                if let Some(skin) = gltf_node.skin() {
+                    entity_to_skin_index_map.insert(node, skin.index());
+                }
             }
         }
 
@@ -723,7 +791,15 @@ fn load_node(
 
         // append other nodes
         for child in gltf_node.children() {
-            if let Err(err) = load_node(&child, parent, load_context, buffer_data, animated_nodes) {
+            if let Err(err) = load_node(
+                &child,
+                parent,
+                load_context,
+                buffer_data,
+                animated_nodes,
+                node_index_to_entity_map,
+                entity_to_skin_index_map,
+            ) {
                 gltf_error = Some(err);
                 return;
             }
@@ -770,6 +846,10 @@ fn scene_label(scene: &gltf::Scene) -> String {
     format!("Scene{}", scene.index())
 }
 
+fn skin_label(skin: &gltf::Skin) -> String {
+    format!("Skin{}", skin.index())
+}
+
 /// Extracts the texture sampler data from the glTF texture.
 fn texture_sampler<'a>(texture: &gltf::Texture) -> SamplerDescriptor<'a> {
     let gltf_sampler = texture.sampler();

crates/bevy_pbr/Cargo.toml

@@ -29,3 +29,4 @@ bevy_window = { path = "../bevy_window", version = "0.7.0-dev" }
 bitflags = "1.2"
 # direct dependency required for derive macro
 bytemuck = { version = "1", features = ["derive"] }
+smallvec = "1.0"

crates/bevy_pbr/src/material.rs

@@ -245,11 +245,11 @@ impl<M: SpecializedMaterial> SpecializedMeshPipeline for MaterialPipeline<M> {
         if let Some(fragment_shader) = &self.fragment_shader {
             descriptor.fragment.as_mut().unwrap().shader = fragment_shader.clone();
         }
-        descriptor.layout = Some(vec![
+
-            self.mesh_pipeline.view_layout.clone(),
+        // MeshPipeline::specialize's current implementation guarantees that the returned
-            self.material_layout.clone(),
+        // specialized descriptor has a populated layout
-            self.mesh_pipeline.mesh_layout.clone(),
+        let descriptor_layout = descriptor.layout.as_mut().unwrap();
-        ]);
+        descriptor_layout.insert(1, self.material_layout.clone());
 
         M::specialize(&mut descriptor, key.material_key, layout)?;
         Ok(descriptor)

crates/bevy_pbr/src/render/depth.wgsl

@@ -12,8 +12,18 @@ var<uniform> view: View;
 [[group(1), binding(0)]]
 var<uniform> mesh: Mesh;
 
+#ifdef SKINNED
+[[group(1), binding(1)]]
+var<uniform> joint_matrices: SkinnedMesh;
+#import bevy_pbr::skinning
+#endif
+
 struct Vertex {
     [[location(0)]] position: vec3<f32>;
+#ifdef SKINNED
+    [[location(4)]] joint_indices: vec4<u32>;
+    [[location(5)]] joint_weights: vec4<f32>;
+#endif
 };
 
 struct VertexOutput {
@@ -22,7 +32,13 @@ struct VertexOutput {
 
 [[stage(vertex)]]
 fn vertex(vertex: Vertex) -> VertexOutput {
+#ifdef SKINNED
+    let model = skin_model(vertex.joint_indices, vertex.joint_weights);
+#else
+    let model = mesh.model;
+#endif
+
     var out: VertexOutput;
-    out.clip_position = view.view_proj * mesh.model * vec4<f32>(vertex.position, 1.0);
+    out.clip_position = view.view_proj * model * vec4<f32>(vertex.position, 1.0);
     return out;
 }

crates/bevy_pbr/src/render/light.rs

@@ -159,6 +159,7 @@ pub const SHADOW_FORMAT: TextureFormat = TextureFormat::Depth32Float;
 pub struct ShadowPipeline {
     pub view_layout: BindGroupLayout,
     pub mesh_layout: BindGroupLayout,
+    pub skinned_mesh_layout: BindGroupLayout,
     pub point_light_sampler: Sampler,
     pub directional_light_sampler: Sampler,
 }
@@ -187,10 +188,12 @@ impl FromWorld for ShadowPipeline {
         });
 
         let mesh_pipeline = world.get_resource::<MeshPipeline>().unwrap();
+        let skinned_mesh_layout = mesh_pipeline.skinned_mesh_layout.clone();
 
         ShadowPipeline {
             view_layout,
             mesh_layout: mesh_pipeline.mesh_layout.clone(),
+            skinned_mesh_layout,
             point_light_sampler: render_device.create_sampler(&SamplerDescriptor {
                 address_mode_u: AddressMode::ClampToEdge,
                 address_mode_v: AddressMode::ClampToEdge,
@@ -256,18 +259,31 @@ impl SpecializedMeshPipeline for ShadowPipeline {
         key: Self::Key,
         layout: &MeshVertexBufferLayout,
     ) -> Result<RenderPipelineDescriptor, SpecializedMeshPipelineError> {
-        let vertex_buffer_layout =
+        let mut vertex_attributes = vec![Mesh::ATTRIBUTE_POSITION.at_shader_location(0)];
-            layout.get_layout(&[Mesh::ATTRIBUTE_POSITION.at_shader_location(0)])?;
+
+        let mut bind_group_layout = vec![self.view_layout.clone(), self.mesh_layout.clone()];
+        let mut shader_defs = Vec::new();
+
+        if layout.contains(Mesh::ATTRIBUTE_JOINT_INDEX)
+            && layout.contains(Mesh::ATTRIBUTE_JOINT_WEIGHT)
+        {
+            shader_defs.push(String::from("SKINNED"));
+            vertex_attributes.push(Mesh::ATTRIBUTE_JOINT_INDEX.at_shader_location(4));
+            vertex_attributes.push(Mesh::ATTRIBUTE_JOINT_WEIGHT.at_shader_location(5));
+            bind_group_layout.push(self.skinned_mesh_layout.clone());
+        }
+
+        let vertex_buffer_layout = layout.get_layout(&vertex_attributes)?;
 
         Ok(RenderPipelineDescriptor {
             vertex: VertexState {
                 shader: SHADOW_SHADER_HANDLE.typed::<Shader>(),
                 entry_point: "vertex".into(),
-                shader_defs: vec![],
+                shader_defs,
                 buffers: vec![vertex_buffer_layout],
             },
             fragment: None,
-            layout: Some(vec![self.view_layout.clone(), self.mesh_layout.clone()]),
+            layout: Some(bind_group_layout),
             primitive: PrimitiveState {
                 topology: key.primitive_topology(),
                 strip_index_format: None,

crates/bevy_pbr/src/render/mesh.rs

@@ -3,7 +3,7 @@ use crate::{
     ViewClusterBindings, ViewLightsUniformOffset, ViewShadowBindings,
 };
 use bevy_app::Plugin;
-use bevy_asset::{load_internal_asset, Handle, HandleUntyped};
+use bevy_asset::{load_internal_asset, Assets, Handle, HandleUntyped};
 use bevy_ecs::{
     prelude::*,
     system::{lifetimeless::*, SystemParamItem},
@@ -11,7 +11,10 @@ use bevy_ecs::{
 use bevy_math::{Mat4, Size};
 use bevy_reflect::TypeUuid;
 use bevy_render::{
-    mesh::{GpuBufferInfo, Mesh, MeshVertexBufferLayout},
+    mesh::{
+        skinning::{SkinnedMesh, SkinnedMeshInverseBindposes},
+        GpuBufferInfo, Mesh, MeshVertexBufferLayout,
+    },
     render_asset::RenderAssets,
     render_component::{ComponentUniforms, DynamicUniformIndex, UniformComponentPlugin},
     render_phase::{EntityRenderCommand, RenderCommandResult, TrackedRenderPass},
@@ -22,16 +25,24 @@ use bevy_render::{
     RenderApp, RenderStage,
 };
 use bevy_transform::components::GlobalTransform;
+use smallvec::SmallVec;
+use std::num::NonZeroU64;
 
 #[derive(Default)]
 pub struct MeshRenderPlugin;
 
+const MAX_JOINTS: usize = 256;
+const JOINT_SIZE: usize = std::mem::size_of::<Mat4>();
+pub(crate) const JOINT_BUFFER_SIZE: usize = MAX_JOINTS * JOINT_SIZE;
+
 pub const MESH_VIEW_BIND_GROUP_HANDLE: HandleUntyped =
     HandleUntyped::weak_from_u64(Shader::TYPE_UUID, 9076678235888822571);
 pub const MESH_STRUCT_HANDLE: HandleUntyped =
     HandleUntyped::weak_from_u64(Shader::TYPE_UUID, 2506024101911992377);
 pub const MESH_SHADER_HANDLE: HandleUntyped =
     HandleUntyped::weak_from_u64(Shader::TYPE_UUID, 3252377289100772450);
+pub const SKINNING_HANDLE: HandleUntyped =
+    HandleUntyped::weak_from_u64(Shader::TYPE_UUID, 13215291596265391738);
 
 impl Plugin for MeshRenderPlugin {
     fn build(&self, app: &mut bevy_app::App) {
@@ -48,13 +59,17 @@ impl Plugin for MeshRenderPlugin {
             "mesh_view_bind_group.wgsl",
             Shader::from_wgsl
         );
+        load_internal_asset!(app, SKINNING_HANDLE, "skinning.wgsl", Shader::from_wgsl);
 
         app.add_plugin(UniformComponentPlugin::<MeshUniform>::default());
 
         if let Ok(render_app) = app.get_sub_app_mut(RenderApp) {
             render_app
                 .init_resource::<MeshPipeline>()
+                .init_resource::<SkinnedMeshUniform>()
                 .add_system_to_stage(RenderStage::Extract, extract_meshes)
+                .add_system_to_stage(RenderStage::Extract, extract_skinned_meshes)
+                .add_system_to_stage(RenderStage::Prepare, prepare_skinned_meshes)
                 .add_system_to_stage(RenderStage::Queue, queue_mesh_bind_group)
                 .add_system_to_stage(RenderStage::Queue, queue_mesh_view_bind_groups);
         }
@@ -129,7 +144,7 @@ pub fn extract_meshes(
     commands.insert_or_spawn_batch(caster_values);
 
     let mut not_caster_values = Vec::with_capacity(*previous_not_caster_len);
-    for (entity, computed_visibility, transform, handle, not_receiver) in not_caster_query.iter() {
+    for (entity, computed_visibility, transform, mesh, not_receiver) in not_caster_query.iter() {
         if !computed_visibility.is_visible {
             continue;
         }
@@ -137,7 +152,7 @@ pub fn extract_meshes(
         not_caster_values.push((
             entity,
             (
-                handle.clone_weak(),
+                mesh.clone_weak(),
                 MeshUniform {
                     flags: if not_receiver.is_some() {
                         MeshFlags::empty().bits
@@ -155,10 +170,92 @@ pub fn extract_meshes(
     commands.insert_or_spawn_batch(not_caster_values);
 }
 
+#[derive(Debug, Default)]
+pub struct ExtractedJoints {
+    pub buffer: Vec<Mat4>,
+}
+
+#[derive(Component)]
+pub struct SkinnedMeshJoints {
+    pub index: u32,
+}
+
+impl SkinnedMeshJoints {
+    #[inline]
+    pub fn build(
+        skin: &SkinnedMesh,
+        inverse_bindposes: &Assets<SkinnedMeshInverseBindposes>,
+        joints: &Query<&GlobalTransform>,
+        buffer: &mut Vec<Mat4>,
+    ) -> Option<Self> {
+        let inverse_bindposes = inverse_bindposes.get(&skin.inverse_bindposes)?;
+        let bindposes = inverse_bindposes.iter();
+        let skin_joints = skin.joints.iter();
+        let mut temp =
+            SmallVec::<[Mat4; MAX_JOINTS]>::with_capacity(bindposes.len().min(MAX_JOINTS));
+        for (inverse_bindpose, joint) in bindposes.zip(skin_joints).take(MAX_JOINTS) {
+            let joint_matrix = joints.get(*joint).ok()?.compute_matrix();
+            temp.push(joint_matrix * *inverse_bindpose);
+        }
+
+        let start = buffer.len();
+        buffer.extend(temp);
+        // Pad to 256 byte alignment
+        while buffer.len() % 4 != 0 {
+            buffer.push(Mat4::ZERO);
+        }
+        Some(Self {
+            index: start as u32,
+        })
+    }
+
+    pub fn to_buffer_index(mut self) -> Self {
+        self.index *= std::mem::size_of::<Mat4>() as u32;
+        self
+    }
+}
+
+pub fn extract_skinned_meshes(
+    query: Query<(Entity, &ComputedVisibility, &SkinnedMesh)>,
+    inverse_bindposes: Res<Assets<SkinnedMeshInverseBindposes>>,
+    joint_query: Query<&GlobalTransform>,
+    mut commands: Commands,
+    mut previous_len: Local<usize>,
+    mut previous_joint_len: Local<usize>,
+) {
+    let mut values = Vec::with_capacity(*previous_len);
+    let mut joints = Vec::with_capacity(*previous_joint_len);
+    let mut last_start = 0;
+
+    for (entity, computed_visibility, skin) in query.iter() {
+        if !computed_visibility.is_visible {
+            continue;
+        }
+        // PERF: This can be expensive, can we move this to prepare?
+        if let Some(skinned_joints) =
+            SkinnedMeshJoints::build(skin, &inverse_bindposes, &joint_query, &mut joints)
+        {
+            last_start = last_start.max(skinned_joints.index as usize);
+            values.push((entity, (skinned_joints.to_buffer_index(),)));
+        }
+    }
+
+    // Pad out the buffer to ensure that there's enough space for bindings
+    while joints.len() - last_start < MAX_JOINTS {
+        joints.push(Mat4::ZERO);
+    }
+
+    *previous_len = values.len();
+    *previous_joint_len = joints.len();
+    commands.insert_resource(ExtractedJoints { buffer: joints });
+    commands.insert_or_spawn_batch(values);
+}
+
 #[derive(Clone)]
 pub struct MeshPipeline {
     pub view_layout: BindGroupLayout,
     pub mesh_layout: BindGroupLayout,
+    pub skinned_mesh_layout: BindGroupLayout,
     // This dummy white texture is to be used in place of optional StandardMaterial textures
     pub dummy_white_gpu_image: GpuImage,
 }
@@ -276,8 +373,7 @@ impl FromWorld for MeshPipeline {
             label: Some("mesh_view_layout"),
         });
 
-        let mesh_layout = render_device.create_bind_group_layout(&BindGroupLayoutDescriptor {
+        let mesh_binding = BindGroupLayoutEntry {
-            entries: &[BindGroupLayoutEntry {
             binding: 0,
             visibility: ShaderStages::VERTEX | ShaderStages::FRAGMENT,
             ty: BindingType::Buffer {
@@ -286,9 +382,31 @@ impl FromWorld for MeshPipeline {
                 min_binding_size: BufferSize::new(MeshUniform::std140_size_static() as u64),
             },
             count: None,
-            }],
+        };
+
+        let mesh_layout = render_device.create_bind_group_layout(&BindGroupLayoutDescriptor {
+            entries: &[mesh_binding],
             label: Some("mesh_layout"),
         });
+
+        let skinned_mesh_layout =
+            render_device.create_bind_group_layout(&BindGroupLayoutDescriptor {
+                entries: &[
+                    mesh_binding,
+                    BindGroupLayoutEntry {
+                        binding: 1,
+                        visibility: ShaderStages::VERTEX,
+                        ty: BindingType::Buffer {
+                            ty: BufferBindingType::Uniform,
+                            has_dynamic_offset: true,
+                            min_binding_size: BufferSize::new(JOINT_BUFFER_SIZE as u64),
+                        },
+                        count: None,
+                    },
+                ],
+                label: Some("skinned_mesh_layout"),
+            });
+
         // A 1x1x1 'all 1.0' texture to use as a dummy texture to use in place of optional StandardMaterial textures
         let dummy_white_gpu_image = {
             let image = Image::new_fill(
@@ -338,6 +456,7 @@ impl FromWorld for MeshPipeline {
         MeshPipeline {
             view_layout,
             mesh_layout,
+            skinned_mesh_layout,
             dummy_white_gpu_image,
         }
     }
@@ -429,6 +548,18 @@ impl SpecializedMeshPipeline for MeshPipeline {
             vertex_attributes.push(Mesh::ATTRIBUTE_TANGENT.at_shader_location(3));
         }
 
+        let mut bind_group_layout = vec![self.view_layout.clone()];
+        if layout.contains(Mesh::ATTRIBUTE_JOINT_INDEX)
+            && layout.contains(Mesh::ATTRIBUTE_JOINT_WEIGHT)
+        {
+            shader_defs.push(String::from("SKINNED"));
+            vertex_attributes.push(Mesh::ATTRIBUTE_JOINT_INDEX.at_shader_location(4));
+            vertex_attributes.push(Mesh::ATTRIBUTE_JOINT_WEIGHT.at_shader_location(5));
+            bind_group_layout.push(self.skinned_mesh_layout.clone());
+        } else {
+            bind_group_layout.push(self.mesh_layout.clone());
+        };
+
         let vertex_buffer_layout = layout.get_layout(&vertex_attributes)?;
 
         let (label, blend, depth_write_enabled);
@@ -467,7 +598,7 @@ impl SpecializedMeshPipeline for MeshPipeline {
                     write_mask: ColorWrites::ALL,
                 }],
             }),
-            layout: Some(vec![self.view_layout.clone(), self.mesh_layout.clone()]),
+            layout: Some(bind_group_layout),
             primitive: PrimitiveState {
                 front_face: FrontFace::Ccw,
                 cull_mode: Some(Face::Back),
@@ -504,7 +635,8 @@ impl SpecializedMeshPipeline for MeshPipeline {
 }
 
 pub struct MeshBindGroup {
-    pub value: BindGroup,
+    pub normal: BindGroup,
+    pub skinned: Option<BindGroup>,
 }
 
 pub fn queue_mesh_bind_group(
@@ -512,19 +644,70 @@ pub fn queue_mesh_bind_group(
     mesh_pipeline: Res<MeshPipeline>,
     render_device: Res<RenderDevice>,
     mesh_uniforms: Res<ComponentUniforms<MeshUniform>>,
+    skinned_mesh_uniform: Res<SkinnedMeshUniform>,
 ) {
-    if let Some(binding) = mesh_uniforms.uniforms().binding() {
+    if let Some(mesh_binding) = mesh_uniforms.uniforms().binding() {
-        commands.insert_resource(MeshBindGroup {
+        let mut mesh_bind_group = MeshBindGroup {
-            value: render_device.create_bind_group(&BindGroupDescriptor {
+            normal: render_device.create_bind_group(&BindGroupDescriptor {
                 entries: &[BindGroupEntry {
                     binding: 0,
-                    resource: binding,
+                    resource: mesh_binding.clone(),
                 }],
                 label: Some("mesh_bind_group"),
                 layout: &mesh_pipeline.mesh_layout,
             }),
-        });
+            skinned: None,
+        };
+
+        if let Some(skinned_joints_buffer) = skinned_mesh_uniform.buffer.uniform_buffer() {
+            mesh_bind_group.skinned = Some(render_device.create_bind_group(&BindGroupDescriptor {
+                entries: &[
+                    BindGroupEntry {
+                        binding: 0,
+                        resource: mesh_binding,
+                    },
+                    BindGroupEntry {
+                        binding: 1,
+                        resource: BindingResource::Buffer(BufferBinding {
+                            buffer: skinned_joints_buffer,
+                            offset: 0,
+                            size: Some(NonZeroU64::new(JOINT_BUFFER_SIZE as u64).unwrap()),
+                        }),
+                    },
+                ],
+                label: Some("skinned_mesh_bind_group"),
+                layout: &mesh_pipeline.skinned_mesh_layout,
+            }));
         }
+        commands.insert_resource(mesh_bind_group);
+    }
+}
+
+#[derive(Default)]
+pub struct SkinnedMeshUniform {
+    pub buffer: UniformVec<Mat4>,
+}
+
+pub fn prepare_skinned_meshes(
+    render_device: Res<RenderDevice>,
+    render_queue: Res<RenderQueue>,
+    extracted_joints: Res<ExtractedJoints>,
+    mut skinned_mesh_uniform: ResMut<SkinnedMeshUniform>,
+) {
+    if extracted_joints.buffer.is_empty() {
+        return;
+    }
+
+    skinned_mesh_uniform.buffer.clear();
+    skinned_mesh_uniform
+        .buffer
+        .reserve(extracted_joints.buffer.len(), &render_device);
+    for joint in extracted_joints.buffer.iter() {
+        skinned_mesh_uniform.buffer.push(*joint);
+    }
+    skinned_mesh_uniform
+        .buffer
+        .write_buffer(&render_device, &render_queue);
 }
 
 #[derive(Component)]
@@ -640,7 +823,10 @@ pub struct SetMeshBindGroup<const I: usize>;
 impl<const I: usize> EntityRenderCommand for SetMeshBindGroup<I> {
     type Param = (
         SRes<MeshBindGroup>,
-        SQuery<Read<DynamicUniformIndex<MeshUniform>>>,
+        SQuery<(
+            Read<DynamicUniformIndex<MeshUniform>>,
+            Option<Read<SkinnedMeshJoints>>,
+        )>,
     );
     #[inline]
     fn render<'w>(
@@ -649,12 +835,20 @@ impl<const I: usize> EntityRenderCommand for SetMeshBindGroup<I> {
         (mesh_bind_group, mesh_query): SystemParamItem<'w, '_, Self::Param>,
         pass: &mut TrackedRenderPass<'w>,
     ) -> RenderCommandResult {
-        let mesh_index = mesh_query.get(item).unwrap();
+        let (mesh_index, skinned_mesh_joints) = mesh_query.get(item).unwrap();
+        if let Some(joints) = skinned_mesh_joints {
             pass.set_bind_group(
                 I,
-            &mesh_bind_group.into_inner().value,
+                mesh_bind_group.into_inner().skinned.as_ref().unwrap(),
+                &[mesh_index.index(), joints.index],
+            );
+        } else {
+            pass.set_bind_group(
+                I,
+                &mesh_bind_group.into_inner().normal,
                 &[mesh_index.index()],
             );
+        }
         RenderCommandResult::Success
     }
 }

crates/bevy_pbr/src/render/mesh.wgsl

@@ -8,6 +8,10 @@ struct Vertex {
 #ifdef VERTEX_TANGENTS
     [[location(3)]] tangent: vec4<f32>;
 #endif
+#ifdef SKINNED
+    [[location(4)]] joint_indices: vec4<u32>;
+    [[location(5)]] joint_weights: vec4<f32>;
+#endif
 };
 
 struct VertexOutput {
@@ -22,15 +26,24 @@ struct VertexOutput {
 
 [[group(2), binding(0)]]
 var<uniform> mesh: Mesh;
+#ifdef SKINNED
+[[group(2), binding(1)]]
+var<uniform> joint_matrices: SkinnedMesh;
+#import bevy_pbr::skinning
+#endif
 
 [[stage(vertex)]]
 fn vertex(vertex: Vertex) -> VertexOutput {
-    let world_position = mesh.model * vec4<f32>(vertex.position, 1.0);
-
     var out: VertexOutput;
-    out.uv = vertex.uv;
+#ifdef SKINNED
-    out.world_position = world_position;
+    var model = skin_model(vertex.joint_indices, vertex.joint_weights);
-    out.clip_position = view.view_proj * world_position;
+    out.world_position = model * vec4<f32>(vertex.position, 1.0);
+    out.world_normal = skin_normals(model, vertex.normal);
+#ifdef VERTEX_TANGENTS
+    out.world_tangent = skin_tangents(model, vertex.tangent);
+#endif
+#else
+    out.world_position = mesh.model * vec4<f32>(vertex.position, 1.0);
     out.world_normal = mat3x3<f32>(
         mesh.inverse_transpose_model[0].xyz,
         mesh.inverse_transpose_model[1].xyz,
@@ -46,6 +59,10 @@ fn vertex(vertex: Vertex) -> VertexOutput {
         vertex.tangent.w
     );
 #endif
+#endif
+
+    out.uv = vertex.uv;
+    out.clip_position = view.view_proj * out.world_position;
     return out;
 }
 

crates/bevy_pbr/src/render/mesh_struct.wgsl

@@ -7,4 +7,10 @@ struct Mesh {
     flags: u32;
 };
 
+#ifdef SKINNED
+struct SkinnedMesh {
+    data: array<mat4x4<f32>, 256u>;
+};
+#endif
+
 let MESH_FLAGS_SHADOW_RECEIVER_BIT: u32 = 1u;

crates/bevy_pbr/src/render/skinning.wgsl

@@ -0,0 +1,66 @@
+// If using this WGSL snippet as an #import, a dedicated 
+// "joint_matricies" uniform of type SkinnedMesh must be added in the
+// main shader.
+
+#define_import_path bevy_pbr::skinning
+
+/// HACK: This works around naga not supporting matrix addition in SPIR-V 
+// translations. See https://github.com/gfx-rs/naga/issues/1527
+fn add_matrix(
+    a: mat4x4<f32>,
+    b: mat4x4<f32>,
+) -> mat4x4<f32> {
+    return mat4x4<f32>(
+        a.x + b.x,
+        a.y + b.y,
+        a.z + b.z,
+        a.w + b.w,
+    );
+}
+
+fn skin_model(
+    indexes: vec4<u32>,
+    weights: vec4<f32>,
+) -> mat4x4<f32> {
+    var matrix = weights.x * joint_matrices.data[indexes.x];
+    matrix = add_matrix(matrix, weights.y * joint_matrices.data[indexes.y]);
+    matrix = add_matrix(matrix, weights.z * joint_matrices.data[indexes.z]);
+    return add_matrix(matrix, weights.w * joint_matrices.data[indexes.w]);
+}
+
+fn inverse_transpose_3x3(in: mat3x3<f32>) -> mat3x3<f32> {
+    let x = cross(in.y, in.z);
+    let y = cross(in.z, in.x); 
+    let z = cross(in.x, in.y);
+    let det = dot(in.z, z);
+    return mat3x3<f32>(
+        x / det,
+        y / det,
+        z / det
+    );
+}
+
+fn skin_normals(
+    model: mat4x4<f32>,
+    normal: vec3<f32>,
+) -> vec3<f32> {
+    return inverse_transpose_3x3(mat3x3<f32>(
+        model[0].xyz,
+        model[1].xyz,
+        model[2].xyz
+    )) * normal;
+}
+
+fn skin_tangents(
+    model: mat4x4<f32>,
+    tangent: vec4<f32>,
+) -> vec4<f32> {
+    return vec4<f32>(
+        mat3x3<f32>(
+            model[0].xyz,
+            model[1].xyz,
+            model[2].xyz
+        ) * tangent.xyz,
+        tangent.w
+    );
+}

crates/bevy_pbr/src/render/wireframe.wgsl

@@ -3,6 +3,10 @@
 
 struct Vertex {
     [[location(0)]] position: vec3<f32>;
+#ifdef SKINNED
+    [[location(4)]] joint_indexes: vec4<u32>;
+    [[location(5)]] joint_weights: vec4<f32>;
+#endif
 };
 
 [[group(1), binding(0)]]
@@ -12,10 +16,21 @@ struct VertexOutput {
     [[builtin(position)]] clip_position: vec4<f32>;
 };
 
+#ifdef SKINNED
+[[group(2), binding(0)]]
+var<uniform> joint_matrices: SkinnedMesh;
+#import bevy_pbr::skinning
+#endif
+
 [[stage(vertex)]]
 fn vertex(vertex: Vertex) -> VertexOutput {
-    let world_position = mesh.model * vec4<f32>(vertex.position, 1.0);
+#ifdef SKINNED
+    let model = skin_model(vertex.joint_indexes, vertex.joint_weights);
+#else
+    let model = mesh.model;
+#endif
 
+    let world_position = model * vec4<f32>(vertex.position, 1.0);
     var out: VertexOutput;
     out.clip_position = view.view_proj * world_position;
 

crates/bevy_render/src/mesh/mesh/conversions.rs

@@ -118,6 +118,12 @@ impl From<Vec<[u32; 4]>> for VertexAttributeValues {
     }
 }
 
+impl From<Vec<[u16; 4]>> for VertexAttributeValues {
+    fn from(vec: Vec<[u16; 4]>) -> Self {
+        VertexAttributeValues::Uint16x4(vec)
+    }
+}
+
 impl From<Vec<[u8; 4]>> for VertexAttributeValues {
     fn from(vec: Vec<[u8; 4]>) -> Self {
         VertexAttributeValues::Unorm8x4(vec)

crates/bevy_render/src/mesh/mesh/mod.rs

@@ -1,4 +1,6 @@
 mod conversions;
+pub mod skinning;
+pub use wgpu::PrimitiveTopology;
 
 use crate::{
     primitives::Aabb,
@@ -14,8 +16,8 @@ use bevy_utils::{EnumVariantMeta, Hashed};
 use std::{collections::BTreeMap, hash::Hash};
 use thiserror::Error;
 use wgpu::{
-    util::BufferInitDescriptor, BufferUsages, IndexFormat, PrimitiveTopology, VertexAttribute,
+    util::BufferInitDescriptor, BufferUsages, IndexFormat, VertexAttribute, VertexFormat,
-    VertexFormat, VertexStepMode,
+    VertexStepMode,
 };
 
 pub const INDEX_BUFFER_ASSET_INDEX: u64 = 0;
@@ -78,7 +80,7 @@ impl Mesh {
         MeshVertexAttribute::new("Vertex_JointWeight", 5, VertexFormat::Float32x4);
     /// Per vertex joint transform matrix index. Use in conjunction with [`Mesh::insert_attribute`]
     pub const ATTRIBUTE_JOINT_INDEX: MeshVertexAttribute =
-        MeshVertexAttribute::new("Vertex_JointIndex", 6, VertexFormat::Uint32);
+        MeshVertexAttribute::new("Vertex_JointIndex", 6, VertexFormat::Uint16x4);
 
     /// Construct a new mesh. You need to provide a [`PrimitiveTopology`] so that the
     /// renderer knows how to treat the vertex data. Most of the time this will be

crates/bevy_render/src/mesh/mesh/skinning.rs

@@ -0,0 +1,44 @@
+use bevy_asset::Handle;
+use bevy_ecs::{
+    component::Component,
+    entity::{Entity, EntityMap, MapEntities, MapEntitiesError},
+    prelude::ReflectComponent,
+    reflect::ReflectMapEntities,
+};
+use bevy_math::Mat4;
+use bevy_reflect::{Reflect, TypeUuid};
+use std::ops::Deref;
+
+#[derive(Component, Debug, Default, Clone, Reflect)]
+#[reflect(Component, MapEntities)]
+pub struct SkinnedMesh {
+    pub inverse_bindposes: Handle<SkinnedMeshInverseBindposes>,
+    pub joints: Vec<Entity>,
+}
+
+impl MapEntities for SkinnedMesh {
+    fn map_entities(&mut self, entity_map: &EntityMap) -> Result<(), MapEntitiesError> {
+        for joint in &mut self.joints {
+            *joint = entity_map.get(*joint)?;
+        }
+
+        Ok(())
+    }
+}
+
+#[derive(Debug, TypeUuid)]
+#[uuid = "b9f155a9-54ec-4026-988f-e0a03e99a76f"]
+pub struct SkinnedMeshInverseBindposes(Box<[Mat4]>);
+
+impl From<Vec<Mat4>> for SkinnedMeshInverseBindposes {
+    fn from(value: Vec<Mat4>) -> Self {
+        Self(value.into_boxed_slice())
+    }
+}
+
+impl Deref for SkinnedMeshInverseBindposes {
+    type Target = [Mat4];
+    fn deref(&self) -> &Self::Target {
+        &*self.0
+    }
+}

crates/bevy_render/src/mesh/mod.rs

@@ -15,6 +15,8 @@ pub struct MeshPlugin;
 impl Plugin for MeshPlugin {
     fn build(&self, app: &mut App) {
         app.add_asset::<Mesh>()
+            .add_asset::<skinning::SkinnedMeshInverseBindposes>()
+            .register_type::<skinning::SkinnedMesh>()
             .add_plugin(RenderAssetPlugin::<Mesh>::default());
     }
 }

examples/README.md

@@ -39,6 +39,7 @@ git checkout v0.4.0
 - [Cross-Platform Examples](#cross-platform-examples)
   - [2D Rendering](#2d-rendering)
   - [3D Rendering](#3d-rendering)
+  - [Animation](#animation)
   - [Application](#application)
   - [Assets](#assets)
   - [Async Tasks](#async-tasks)
@@ -118,6 +119,13 @@ Example | File | Description
 `update_gltf_scene` | [`3d/update_gltf_scene.rs`](./3d/update_gltf_scene.rs) | Update a scene from a gltf file, either by spawning the scene as a child of another entity, or by accessing the entities of the scene
 `wireframe` | [`3d/wireframe.rs`](./3d/wireframe.rs) | Showcases wireframe rendering
 
+## Animation
+
+Example | File | Description
+--- | --- | ---
+`custom_skinned_mesh` | [`animation/custom_skinned_mesh.rs`](./animation/custom_skinned_mesh.rs) | Skinned mesh example with mesh and joints data defined in code.
+`gltf_skinned_mesh` | [`animation/gltf_skinned_mesh.rs`](./animation/gltf_skinned_mesh.rs) | Skinned mesh example with mesh and joints data loaded from a glTF file.
+
 ## Application
 
 Example | File | Description

examples/animation/custom_skinned_mesh.rs

@@ -0,0 +1,171 @@
+use std::f32::consts::PI;
+
+use bevy::{
+    pbr::AmbientLight,
+    prelude::*,
+    render::mesh::{
+        skinning::{SkinnedMesh, SkinnedMeshInverseBindposes},
+        Indices, PrimitiveTopology,
+    },
+};
+use rand::Rng;
+
+/// Skinned mesh example with mesh and joints data defined in code.
+/// Example taken from <https://github.com/KhronosGroup/glTF-Tutorials/blob/master/gltfTutorial/gltfTutorial_019_SimpleSkin.md>
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .insert_resource(AmbientLight {
+            brightness: 1.0,
+            ..Default::default()
+        })
+        .add_startup_system(setup)
+        .add_system(joint_animation)
+        .run();
+}
+
+/// Used to mark a joint to be animated in the [`joint_animation`] system.
+#[derive(Component)]
+struct AnimatedJoint;
+
+/// Construct a mesh and a skeleton with 2 joints for that mesh,
+///   and mark the second joint to be animated.
+/// It is similar to the scene defined in `models/SimpleSkin/SimpleSkin.gltf`
+fn setup(
+    mut commands: Commands,
+    mut meshes: ResMut<Assets<Mesh>>,
+    mut materials: ResMut<Assets<StandardMaterial>>,
+    mut skinned_mesh_inverse_bindposes_assets: ResMut<Assets<SkinnedMeshInverseBindposes>>,
+) {
+    // Create a camera
+    commands.spawn_bundle(PerspectiveCameraBundle {
+        transform: Transform::from_xyz(-2.0, 2.5, 5.0).looking_at(Vec3::ZERO, Vec3::Y),
+        ..default()
+    });
+
+    // Create inverse bindpose matrices for a skeleton consists of 2 joints
+    let inverse_bindposes =
+        skinned_mesh_inverse_bindposes_assets.add(SkinnedMeshInverseBindposes::from(vec![
+            Mat4::from_translation(Vec3::new(-0.5, -1.0, 0.0)),
+            Mat4::from_translation(Vec3::new(-0.5, -1.0, 0.0)),
+        ]));
+
+    // Create a mesh
+    let mut mesh = Mesh::new(PrimitiveTopology::TriangleList);
+    // Set mesh vertex positions
+    mesh.insert_attribute(
+        Mesh::ATTRIBUTE_POSITION,
+        vec![
+            [0.0, 0.0, 0.0],
+            [1.0, 0.0, 0.0],
+            [0.0, 0.5, 0.0],
+            [1.0, 0.5, 0.0],
+            [0.0, 1.0, 0.0],
+            [1.0, 1.0, 0.0],
+            [0.0, 1.5, 0.0],
+            [1.0, 1.5, 0.0],
+            [0.0, 2.0, 0.0],
+            [1.0, 2.0, 0.0],
+        ],
+    );
+    // Set mesh vertex normals
+    mesh.insert_attribute(Mesh::ATTRIBUTE_NORMAL, vec![[0.0, 0.0, 1.0]; 10]);
+    // Set mesh vertex UVs. Although the mesh doesn't have any texture applied,
+    //  UVs are still required by the render pipeline. So these UVs are zeroed out.
+    mesh.insert_attribute(Mesh::ATTRIBUTE_UV_0, vec![[0.0, 0.0]; 10]);
+    // Set mesh vertex joint indices for mesh skinning.
+    // Each vertex gets 4 indices used to address the `JointTransforms` array in the vertex shader
+    //  as well as `SkinnedMeshJoint` array in the `SkinnedMesh` component.
+    // This means that a maximum of 4 joints can affect a single vertex.
+    mesh.insert_attribute(
+        Mesh::ATTRIBUTE_JOINT_INDEX,
+        vec![
+            [0u16, 0, 0, 0],
+            [0, 0, 0, 0],
+            [0, 1, 0, 0],
+            [0, 1, 0, 0],
+            [0, 1, 0, 0],
+            [0, 1, 0, 0],
+            [0, 1, 0, 0],
+            [0, 1, 0, 0],
+            [0, 1, 0, 0],
+            [0, 1, 0, 0],
+        ],
+    );
+    // Set mesh vertex joint weights for mesh skinning.
+    // Each vertex gets 4 joint weights corresponding to the 4 joint indices assigned to it.
+    // The sum of these weights should equal to 1.
+    mesh.insert_attribute(
+        Mesh::ATTRIBUTE_JOINT_WEIGHT,
+        vec![
+            [1.00, 0.00, 0.0, 0.0],
+            [1.00, 0.00, 0.0, 0.0],
+            [0.75, 0.25, 0.0, 0.0],
+            [0.75, 0.25, 0.0, 0.0],
+            [0.50, 0.50, 0.0, 0.0],
+            [0.50, 0.50, 0.0, 0.0],
+            [0.25, 0.75, 0.0, 0.0],
+            [0.25, 0.75, 0.0, 0.0],
+            [0.00, 1.00, 0.0, 0.0],
+            [0.00, 1.00, 0.0, 0.0],
+        ],
+    );
+    // Tell bevy to construct triangles from a list of vertex indices,
+    //  where each 3 vertex indices form an triangle.
+    mesh.set_indices(Some(Indices::U16(vec![
+        0, 1, 3, 0, 3, 2, 2, 3, 5, 2, 5, 4, 4, 5, 7, 4, 7, 6, 6, 7, 9, 6, 9, 8,
+    ])));
+
+    let mesh = meshes.add(mesh);
+    for i in -5..5 {
+        // Create joint entities
+        let joint_0 = commands
+            .spawn_bundle((
+                Transform::from_xyz(i as f32 * 1.5, 0.0, 0.0),
+                GlobalTransform::identity(),
+            ))
+            .id();
+        let joint_1 = commands
+            .spawn_bundle((
+                AnimatedJoint,
+                Transform::identity(),
+                GlobalTransform::identity(),
+            ))
+            .id();
+
+        // Set joint_1 as a child of joint_0.
+        commands.entity(joint_0).push_children(&[joint_1]);
+
+        // Each joint in this vector corresponds to each inverse bindpose matrix in `SkinnedMeshInverseBindposes`.
+        let joint_entities = vec![joint_0, joint_1];
+
+        // Create skinned mesh renderer. Note that its transform doesn't affect the position of the mesh.
+        commands
+            .spawn_bundle(PbrBundle {
+                mesh: mesh.clone(),
+                material: materials.add(
+                    Color::rgb(
+                        rand::thread_rng().gen_range(0.0..1.0),
+                        rand::thread_rng().gen_range(0.0..1.0),
+                        rand::thread_rng().gen_range(0.0..1.0),
+                    )
+                    .into(),
+                ),
+                ..Default::default()
+            })
+            .insert(SkinnedMesh {
+                inverse_bindposes: inverse_bindposes.clone(),
+                joints: joint_entities,
+            });
+    }
+}
+
+/// Animate the joint marked with [`AnimatedJoint`] component.
+fn joint_animation(time: Res<Time>, mut query: Query<&mut Transform, With<AnimatedJoint>>) {
+    for mut transform in query.iter_mut() {
+        transform.rotation = Quat::from_axis_angle(
+            Vec3::Z,
+            0.5 * PI * time.time_since_startup().as_secs_f32().sin(),
+        );
+    }
+}

examples/animation/gltf_skinned_mesh.rs

@@ -0,0 +1,70 @@
+use std::f32::consts::PI;
+
+use bevy::{pbr::AmbientLight, prelude::*, render::mesh::skinning::SkinnedMesh};
+
+/// Skinned mesh example with mesh and joints data loaded from a glTF file.
+/// Example taken from <https://github.com/KhronosGroup/glTF-Tutorials/blob/master/gltfTutorial/gltfTutorial_019_SimpleSkin.md>
+fn main() {
+    App::new()
+        .add_plugins(DefaultPlugins)
+        .insert_resource(AmbientLight {
+            brightness: 1.0,
+            ..Default::default()
+        })
+        .add_startup_system(setup)
+        .add_system(joint_animation)
+        .run();
+}
+
+fn setup(mut commands: Commands, asset_server: Res<AssetServer>) {
+    // Create a camera
+    commands.spawn_bundle(PerspectiveCameraBundle {
+        transform: Transform::from_xyz(-2.0, 2.5, 5.0).looking_at(Vec3::ZERO, Vec3::Y),
+        ..default()
+    });
+
+    // Spawn the first scene in `models/SimpleSkin/SimpleSkin.gltf`
+    commands.spawn_scene(asset_server.load::<Scene, _>("models/SimpleSkin/SimpleSkin.gltf#Scene0"));
+}
+
+/// The scene hierachy currently looks somewhat like this:
+///
+/// ```ignore
+/// <Parent entity>
+///   + Mesh node (without `PbrBundle` or `SkinnedMesh` component)
+///     + Skinned mesh entity (with `PbrBundle` and `SkinnedMesh` component, created by glTF loader)
+///     + First joint
+///       + Second joint
+/// ```
+///
+/// In this example, we want to get and animate the second joint.
+/// It is similar to the animation defined in `models/SimpleSkin/SimpleSkin.gltf`.
+fn joint_animation(
+    time: Res<Time>,
+    parent_query: Query<&Parent, With<SkinnedMesh>>,
+    children_query: Query<&Children>,
+    mut transform_query: Query<&mut Transform>,
+) {
+    // Iter skinned mesh entity
+    for skinned_mesh_parent in parent_query.iter() {
+        // Mesh node is the parent of the skinned mesh entity.
+        let mesh_node_entity = skinned_mesh_parent.0;
+        // Get `Children` in the mesh node.
+        let mesh_node_children = children_query.get(mesh_node_entity).unwrap();
+
+        // First joint is the second child of the mesh node.
+        let first_joint_entity = mesh_node_children[1];
+        // Get `Children` in the first joint.
+        let first_joint_children = children_query.get(first_joint_entity).unwrap();
+
+        // Second joint is the first child of the first joint.
+        let second_joint_entity = first_joint_children[0];
+        // Get `Transform` in the second joint.
+        let mut second_joint_transform = transform_query.get_mut(second_joint_entity).unwrap();
+
+        second_joint_transform.rotation = Quat::from_axis_angle(
+            Vec3::Z,
+            0.5 * PI * time.time_since_startup().as_secs_f32().sin(),
+        );
+    }
+}