Meshlet BVH Culling #19318
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Meshlet BVH Culling #19318
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atlv24
added
C-Feature
Readd software raster
SparkyPotato
suggested changes
May 26, 2025
| return min(min(a, b), min(c, d)); | ||
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| // TODO: We should probably be using a POT HZB texture? |
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We should keep this TODO. The current HZB generation is wrong and misses information on the edges of certain mip levels, requiring us to be over-conservative in our culling.
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| fn occlusion_cull_screen_aabb(aabb: ScreenAabb, screen: vec2<f32>) -> bool { | ||
| let hzb_size = ceil(screen); |
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Mip 0 of the HZB is floor(screen * 0.5).
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| // note: add 1 before max because the unsigned overflow behavior is intentional | ||
| // it wraps around firstLeadingBit(0) = ~0 to 0 | ||
| var mip = max(firstLeadingBit(max_size) + 1u, 2u) - 1u; |
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With the above change, I tested the following and it works, letting us sample one mip finer:
// note: add 1 before max because the unsigned overflow behavior is intentional
// it wraps around firstLeadingBit(0) = ~0 to 0
// TODO: we actually sample a 4x4 block, so ideally this would be `max(..., 3u) - 3u`.
// However, since our HZB is not a power of two, we need to be extra-conservative to not over-cull, so we go up a mip.
var mip = max(firstLeadingBit(max_size) + 1u, 2u) - 2u;| let smin = min_texel >> vec2<u32>(mip); | ||
| let smax = max_texel >> vec2<u32>(mip); | ||
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| mip -= 1; |
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With the above changes, this can be removed.
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| // let world_sphere_radius = lod_sphere.w * world_scale; | ||
| // let norm_error = simplification_error / world_sphere_radius * 0.25; | ||
| // return norm_error * view.viewport.w < 1.0; | ||
| let world_error = simplification_error * world_scale; | ||
| let proj = projection[1][1]; | ||
| let height = 2.0 / proj; | ||
| let norm_error = world_error / height; | ||
| return norm_error * view.viewport.w < 1.0; |
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Unsure how correct my change (from the commented code) is, though it seems to work.
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Objective
Solution
Testing