fix cluster tile size calculation

crates/bevy_pbr/src/light.rs

@@ -235,23 +235,29 @@ impl Clusters {
  }
 
  fn from_screen_size_and_z_slices(screen_size: UVec2, z_slices: u32) -> Self {
- let aspect_ratio = screen_size.x as f32 / screen_size.y as f32;
- let n_tiles_y =
- ((ViewClusterBindings::MAX_OFFSETS as u32 / z_slices) as f32 / aspect_ratio).sqrt();
  // NOTE: Round down the number of tiles in order to avoid overflowing the maximum number of
  // clusters.
- let n_tiles = UVec2::new(
- (aspect_ratio * n_tiles_y).floor() as u32,
- n_tiles_y.floor() as u32,
+ let n_tiles_xy = ViewClusterBindings::MAX_OFFSETS as u32 / z_slices;
+ let px_per_tile = 1.max(
+ ((screen_size.x as f32 * screen_size.y as f32) / n_tiles_xy as f32)
+ .sqrt()
+ .floor() as u32,
  );
- Clusters::new((screen_size + UVec2::ONE) / n_tiles, screen_size, Z_SLICES)
+ let n_tiles_x = 1.max(screen_size.x / px_per_tile);
+ let n_tiles_y = 1.max(n_tiles_xy / n_tiles_x);
+ let n_tiles = UVec2::new(n_tiles_x, n_tiles_y);
+
+ // Round *up* tile size, so that the number of tiles calculated in update() below
+ // stays below MAX_OFFSETS
+ let tile_size = UVec2::ONE.max((screen_size + n_tiles - UVec2::ONE) / n_tiles);
+ Clusters::new(tile_size, screen_size, Z_SLICES)
  }
 
  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,
+ 1.max(screen_size.x / tile_size.x),
+ 1.max(screen_size.y / tile_size.y),
  z_slices,
  );
  // NOTE: Maximum 4096 clusters due to uniform buffer size constraints