vello_hybrid implementation
#831
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This brings in the cpu-sparse prototype from the piet-next branch of the piet repo. No substantive changes, but cpu-sparse is renamed vello_hybrid and piet-next is renamed vello_api. Quite a bit of editing to satisfy the lint monster. There was a half-written SIMD implementation of flattening, that's removed. It should be finished and re-added, as it's a good speedup.
Renders a simple scene to the GPU, first by doing coarse rasterization the same as cpu-sparse, then doing a single draw call.
Adds a clip method to the (CPU) render context, plus a considerable amount of mechanism in coarse and fine rasterization to support clipping. The coarse rasterization logic contains a similar set of optimizations as Vello. In particular, all-zero tiles have drawing suppressed, and all-one tiles pass drawing commands through with no additional work to clip. Not extensively validated, but it does render a simple scene with clipping correctly.
DJMcNab
reviewed
Mar 5, 2025
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I'd probably tear out the SIMD code entirely from this version, to make the future refactorings clearer
| let c = b.max(0.0); | ||
| let d = xmin.max(0.0); | ||
| let a = (b + 0.5 * (d * d - c * c) - xmin) / (xmax - xmin); | ||
| areas[x as usize][y] += a * dy; |
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I get a panic on this line:
index out of bounds: the len is 4 but the index is 4, just running:
> cargo run --example gpu
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Fully based on #818, my changes simply relocate the code from the root folder to
sparse_strips/vello_hybrid. Thevello_hybridcode is functional and serves as a good foundation for the next refactoring step, aiming to unifyvello_cpuandvello_hybridcommon components undervello_common.