Split out the IndirectParametersMetadata into CPU-populated and GPU-populated buffers.#17863
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superdump merged 3 commits intobevyengine:mainfrom Feb 18, 2025
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GPU-populated buffers. The GPU can fill out many of the fields in `IndirectParametersMetadata` using information it already has: * `early_instance_count` and `late_instance_count` are always initialized to zero. * `mesh_index` is already present in the work item buffer as the `input_index` of the first work item in each batch. This patch moves these fields to a separate buffer, the *GPU indirect parameters metadata* buffer. That way, it avoids having to write them on CPU during `batch_and_prepare_binned_render_phase`. This effectively reduces the number of bits that that function must write per mesh from 160 to 64 (in addition to the 64 bits per mesh *instance*). Additionally, this PR refactors `UntypedPhaseIndirectParametersBuffers` to add another layer, `MeshClassIndirectParametersBuffers`, which allows abstracting over the buffers corresponding indexed and non-indexed meshes. This patch doesn't make much use of this abstraction, but forthcoming patches will, and it's overall a cleaner approach. This didn't seem to have much of an effect by itself on `batch_and_prepare_binned_render_phase` time, but subsequent PRs dependent on this PR yield roughly a 2× speedup.
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superdump
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Feb 17, 2025
| /// The buffers containing all the information that indirect draw commands use | ||
| /// to draw the scene, for a single mesh class (indexed or non-indexed), for a | ||
| /// single phase. | ||
| pub struct MeshClassIndirectParametersBuffers<IP> |
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While I'm not super keen on the word 'class', I don't have a better suggestion. I like how much gets ripped out of this.
superdump
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Feb 17, 2025
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The GPU can fill out many of the fields in
IndirectParametersMetadatausing information it already has:early_instance_countandlate_instance_countare always initialized to zero.mesh_indexis already present in the work item buffer as theinput_indexof the first work item in each batch.This patch moves these fields to a separate buffer, the GPU indirect parameters metadata buffer. That way, it avoids having to write them on CPU during
batch_and_prepare_binned_render_phase. This effectively reduces the number of bits that that function must write per mesh from 160 to 64 (in addition to the 64 bits per mesh instance).Additionally, this PR refactors
UntypedPhaseIndirectParametersBuffersto add another layer,MeshClassIndirectParametersBuffers, which allows abstracting over the buffers corresponding indexed and non-indexed meshes. This patch doesn't make much use of this abstraction, but forthcoming patches will, and it's overall a cleaner approach.This didn't seem to have much of an effect by itself on
batch_and_prepare_binned_render_phasetime, but subsequent PRs dependent on this PR yield roughly a 2× speedup.