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Directly extract joints into SkinnedMeshJoints (bevyengine#6833)
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# Objective
Following bevyengine#4402, extract systems run on the render world instead of the main world, and allow retained state operations on it's resources. We're currently extracting to `ExtractedJoints` and then copying it twice during Prepare. Once into `SkinnedMeshJoints` and again into the actual GPU buffer.

This makes bevyengine#4902 obsolete.

## Solution
Cut out the middle copy and directly extract joints into `SkinnedMeshJoints` and remove `ExtractedJoints` entirely.

This also removes the per-frame allocation that is being made to send `ExtractedJoints` into the render world.

## Performance
On my local machine, this halves the time for `prepare_skinned _meshes` on `many_foxes` (195.75us -> 93.93us on average).

![image](https://user-images.githubusercontent.com/3137680/205427455-ab91a8a3-a6b0-4f0a-bd48-e54482c563b2.png)

---

## Changelog
Added: `BufferVec::truncate`
Added: `BufferVec::extend`
Changed: `SkinnedMeshJoints::build` now takes a `&mut BufferVec` instead of a `&mut Vec` as a parameter.
Removed: `ExtractedJoints`.

## Migration Guide
`ExtractedJoints` has been removed. Read the bound bones from `SkinnedMeshJoints` instead.
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james7132 authored and ItsDoot committed Feb 1, 2023
1 parent 38dea41 commit 65799a9
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Showing 2 changed files with 32 additions and 31 deletions.
52 changes: 21 additions & 31 deletions crates/bevy_pbr/src/render/mesh.rs
Original file line number Diff line number Diff line change
Expand Up @@ -172,11 +172,6 @@ pub fn extract_meshes(
commands.insert_or_spawn_batch(not_caster_commands);
}

#[derive(Resource, Debug, Default)]
pub struct ExtractedJoints {
pub buffer: Vec<Mat4>,
}

#[derive(Component)]
pub struct SkinnedMeshJoints {
pub index: u32,
Expand All @@ -188,19 +183,22 @@ impl SkinnedMeshJoints {
skin: &SkinnedMesh,
inverse_bindposes: &Assets<SkinnedMeshInverseBindposes>,
joints: &Query<&GlobalTransform>,
buffer: &mut Vec<Mat4>,
buffer: &mut BufferVec<Mat4>,
) -> Option<Self> {
let inverse_bindposes = inverse_bindposes.get(&skin.inverse_bindposes)?;
let bindposes = inverse_bindposes.iter();
let skin_joints = skin.joints.iter();
let start = buffer.len();
for (inverse_bindpose, joint) in bindposes.zip(skin_joints).take(MAX_JOINTS) {
if let Ok(joint) = joints.get(*joint) {
buffer.push(joint.affine() * *inverse_bindpose);
} else {
buffer.truncate(start);
return None;
}
let target = start + skin.joints.len().min(MAX_JOINTS);
buffer.extend(
joints
.iter_many(&skin.joints)
.zip(inverse_bindposes.iter())
.map(|(joint, bindpose)| joint.affine() * *bindpose),
);
// iter_many will skip any failed fetches. This will cause it to assign the wrong bones,
// so just bail by truncating to the start.
if buffer.len() != target {
buffer.truncate(start);
return None;
}

// Pad to 256 byte alignment
Expand All @@ -221,13 +219,13 @@ impl SkinnedMeshJoints {
pub fn extract_skinned_meshes(
mut commands: Commands,
mut previous_len: Local<usize>,
mut previous_joint_len: Local<usize>,
mut uniform: ResMut<SkinnedMeshUniform>,
query: Extract<Query<(Entity, &ComputedVisibility, &SkinnedMesh)>>,
inverse_bindposes: Extract<Res<Assets<SkinnedMeshInverseBindposes>>>,
joint_query: Extract<Query<&GlobalTransform>>,
) {
uniform.buffer.clear();
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 {
Expand All @@ -236,21 +234,19 @@ pub fn extract_skinned_meshes(
}
// 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)
SkinnedMeshJoints::build(skin, &inverse_bindposes, &joint_query, &mut uniform.buffer)
{
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);
while uniform.buffer.len() - last_start < MAX_JOINTS {
uniform.buffer.push(Mat4::ZERO);
}

*previous_len = values.len();
*previous_joint_len = joints.len();
commands.insert_resource(ExtractedJoints { buffer: joints });
commands.insert_or_spawn_batch(values);
}

Expand Down Expand Up @@ -779,20 +775,14 @@ impl Default for SkinnedMeshUniform {
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() {
if skinned_mesh_uniform.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 {
skinned_mesh_uniform.buffer.push(*joint);
}
let len = skinned_mesh_uniform.buffer.len();
skinned_mesh_uniform.buffer.reserve(len, &render_device);
skinned_mesh_uniform
.buffer
.write_buffer(&render_device, &render_queue);
Expand Down
11 changes: 11 additions & 0 deletions crates/bevy_render/src/render_resource/buffer_vec.rs
Original file line number Diff line number Diff line change
Expand Up @@ -131,7 +131,18 @@ impl<T: Pod> BufferVec<T> {
}
}

pub fn truncate(&mut self, len: usize) {
self.values.truncate(len);
}

pub fn clear(&mut self) {
self.values.clear();
}
}

impl<T: Pod> Extend<T> for BufferVec<T> {
#[inline]
fn extend<I: IntoIterator<Item = T>>(&mut self, iter: I) {
self.values.extend(iter);
}
}

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