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bevy_pbr: Optimize assign_lights_to_clusters (#3984)

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# Objective

- Optimize assign_lights_to_clusters

## Solution

- Avoid inserting entities into hash sets in inner loops when it is known they will be inserted in at least one iteration of the loop.
- Use a Vec instead of a hash set where the set is not needed
- Avoid explicit calculation of the cluster_index from x,y,z coordinates, instead using row and column offsets and just adding z in the inner loop 
- These changes cut the time spent in the system roughly in half
This commit is contained in:
Robert Swain 2022-02-28 22:02:06 +00:00
parent 40b36927f5
commit 786654307d
1 changed files with 11 additions and 10 deletions
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21
crates/bevy_pbr/src/light.rs
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@ -478,10 +478,6 @@ fn ndc_position_to_cluster(
.clamp(UVec3::ZERO, cluster_dimensions - UVec3::ONE)
}
fn cluster_to_index(cluster_dimensions: UVec3, cluster: UVec3) -> usize {
((cluster.y * cluster_dimensions.x + cluster.x) * cluster_dimensions.z + cluster.z) as usize
}
// NOTE: Run this before update_point_light_frusta!
pub fn assign_lights_to_clusters(
mut commands: Commands,
@ -506,7 +502,7 @@ pub fn assign_lights_to_clusters(
let mut clusters_lights =
vec![VisiblePointLights::from_light_count(light_count); cluster_count];
let mut visible_lights_set = HashSet::with_capacity(light_count);
let mut visible_lights = Vec::with_capacity(light_count);
for (light_entity, light_transform, light) in lights.iter() {
let light_sphere = Sphere {
@ -519,6 +515,10 @@ pub fn assign_lights_to_clusters(
continue;
}
// NOTE: The light intersects the frustum so it must be visible and part of the global set
global_lights_set.insert(light_entity);
visible_lights.push(light_entity);
// Calculate an AABB for the light in view space, find the corresponding clusters for the min and max
// points of the AABB, then iterate over just those clusters for this light
let light_aabb_view = Aabb {
@ -591,14 +591,14 @@ pub fn assign_lights_to_clusters(
let (min_cluster, max_cluster) =
(min_cluster.min(max_cluster), min_cluster.max(max_cluster));
for y in min_cluster.y..=max_cluster.y {
let row_offset = y * clusters.axis_slices.x;
for x in min_cluster.x..=max_cluster.x {
let col_offset = (row_offset + x) * clusters.axis_slices.z;
for z in min_cluster.z..=max_cluster.z {
let cluster_index =
cluster_to_index(clusters.axis_slices, UVec3::new(x, y, z));
// NOTE: cluster_index = (y * dim.x + x) * dim.z + z
let cluster_index = (col_offset + z) as usize;
let cluster_aabb = &clusters.aabbs[cluster_index];
if light_sphere.intersects_obb(cluster_aabb, &view_transform) {
global_lights_set.insert(light_entity);
visible_lights_set.insert(light_entity);
clusters_lights[cluster_index].entities.push(light_entity);
}
}
@ -611,8 +611,9 @@ pub fn assign_lights_to_clusters(
}
clusters.lights = clusters_lights;
visible_lights.shrink_to_fit();
commands.entity(view_entity).insert(VisiblePointLights {
entities: visible_lights_set.into_iter().collect(),
entities: visible_lights,
});
}
global_lights.entities = global_lights_set.into_iter().collect();