fix cluster tiling calculations (#4148)

# Objective

fix cluster tilesize and tilecount calculations.
Fixes #4127 & #3596

## Solution

- calculate tilesize as smallest integers such that dimensions.xy() tiles will cover the screen
- calculate final dimensions as smallest integers such that final dimensions * tilesize will cover the screen

there is more cleanup that could be done in these functions. a future PR will likely remove the tilesize completely, so this is just a minimal change set to fix the current bug at small screen sizes

Co-authored-by: Carter Anderson <mcanders1@gmail.com>

crates/bevy_pbr/src/light.rs

@@ -293,11 +293,29 @@ impl ClusterConfig {
  total, z_slices, ..
  } => {
  let aspect_ratio = screen_size.x as f32 / screen_size.y as f32;
- let per_layer = *total as f32 / *z_slices as f32;
+ let mut z_slices = *z_slices;
+ if *total < z_slices {
+ warn!("ClusterConfig has more z-slices than total clusters!");
+ z_slices = *total;
+ }
+ let per_layer = *total as f32 / z_slices as f32;
+
  let y = f32::sqrt(per_layer / aspect_ratio);
- let x = (y * aspect_ratio).floor() as u32;
- let y = y.floor() as u32;
- UVec3::new(x, y, *z_slices)
+
+ let mut x = (y * aspect_ratio) as u32;
+ let mut y = y as u32;
+
+ // check extremes
+ if x == 0 {
+ x = 1;
+ y = per_layer as u32;
+ }
+ if y == 0 {
+ x = per_layer as u32;
+ y = 1;
+ }
+
+ UVec3::new(x, y, z_slices)
  }
  }
  }
@@ -369,8 +387,12 @@ impl Clusters {
  near: f32,
  far: f32,
  ) -> Self {
+ debug_assert!(screen_size.x > 0 && screen_size.y > 0);
+ debug_assert!(dimensions.x > 0 && dimensions.y > 0 && dimensions.z > 0);
  Clusters::new(
- (screen_size + UVec2::ONE) / dimensions.xy(),
+ (screen_size.as_vec2() / dimensions.xy().as_vec2())
+ .ceil()
+ .as_uvec2(),
  screen_size,
  dimensions.z,
  near,
@@ -380,13 +402,12 @@ impl Clusters {
 
  fn update(&mut self, tile_size: UVec2, screen_size: UVec2, z_slices: u32) {
  self.tile_size = tile_size;
- self.axis_slices = UVec3::new(
- (screen_size.x + 1) / tile_size.x,
- (screen_size.y + 1) / tile_size.y,
- z_slices,
- );
+ self.axis_slices = (screen_size.as_vec2() / tile_size.as_vec2())
+ .ceil()
+ .as_uvec2()
+ .extend(z_slices);
  // NOTE: Maximum 4096 clusters due to uniform buffer size constraints
- assert!(self.axis_slices.x * self.axis_slices.y * self.axis_slices.z <= 4096);
+ debug_assert!(self.axis_slices.x * self.axis_slices.y * self.axis_slices.z <= 4096);
  }
 }
 
@@ -1240,3 +1261,67 @@ pub fn check_light_mesh_visibility(
  }
  }
 }
+
+#[cfg(test)]
+mod test {
+ use super::*;
+
+ fn test_cluster_tiling(config: ClusterConfig, screen_size: UVec2) -> Clusters {
+ let dims = config.dimensions_for_screen_size(screen_size);
+
+ // note: near & far do not affect tiling
+ let clusters = Clusters::from_screen_size_and_dimensions(screen_size, dims, 5.0, 1000.0);
+
+ // check we cover the screen
+ assert!(clusters.tile_size.x * clusters.axis_slices.x >= screen_size.x);
+ assert!(clusters.tile_size.y * clusters.axis_slices.y >= screen_size.y);
+ // check a smaller number of clusters would not cover the screen
+ assert!(clusters.tile_size.x * (clusters.axis_slices.x - 1) < screen_size.x);
+ assert!(clusters.tile_size.y * (clusters.axis_slices.y - 1) < screen_size.y);
+ // check a smaller tilesize would not cover the screen
+ assert!((clusters.tile_size.x - 1) * clusters.axis_slices.x < screen_size.x);
+ assert!((clusters.tile_size.y - 1) * clusters.axis_slices.y < screen_size.y);
+ // check we don't have more clusters than pixels
+ assert!(clusters.axis_slices.x <= screen_size.x);
+ assert!(clusters.axis_slices.y <= screen_size.y);
+
+ clusters
+ }
+
+ #[test]
+ // check tiling for small screen sizes
+ fn test_default_cluster_setup_small_screensizes() {
+ for x in 1..100 {
+ for y in 1..100 {
+ let screen_size = UVec2::new(x, y);
+ let clusters = test_cluster_tiling(ClusterConfig::default(), screen_size);
+ assert!(
+ clusters.axis_slices.x * clusters.axis_slices.y * clusters.axis_slices.z
+ <= 4096
+ );
+ }
+ }
+ }
+
+ #[test]
+ // check tiling for long thin screen sizes
+ fn test_default_cluster_setup_small_x() {
+ for x in 1..10 {
+ for y in 1..5000 {
+ let screen_size = UVec2::new(x, y);
+ let clusters = test_cluster_tiling(ClusterConfig::default(), screen_size);
+ assert!(
+ clusters.axis_slices.x * clusters.axis_slices.y * clusters.axis_slices.z
+ <= 4096
+ );
+
+ let screen_size = UVec2::new(y, x);
+ let clusters = test_cluster_tiling(ClusterConfig::default(), screen_size);
+ assert!(
+ clusters.axis_slices.x * clusters.axis_slices.y * clusters.axis_slices.z
+ <= 4096
+ );
+ }
+ }
+ }
+}