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Support startVertex/startInstance on DX12 #1725

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kvark opened this issue Jul 26, 2021 · 0 comments · Fixed by #1731
Closed

Support startVertex/startInstance on DX12 #1725

kvark opened this issue Jul 26, 2021 · 0 comments · Fixed by #1731
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area: api Issues related to API surface area: performance How fast things go type: enhancement New feature or request

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kvark commented Jul 26, 2021 •
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Is your feature request related to a problem? Please describe.
DX12 doesn't consider firstVertex/fistInstance to be included into SV_VertexID and SV_InstanceID semantic, but WebGPU requires this.

Describe the solution you'd like
Allocate 2 root constants in front of the signature, then have the shader glue these constants with builtin semantics when asked.
This extra functionality needs to be configurable, since there is a cost to having 2 root constants allocated for each pipeline.

Describe alternatives you've considered
Passing in buffers?

Additional context
We have a test for this, which is quite nice!
@kvark kvark added type: enhancement New feature or request area: api Issues related to API surface area: performance How fast things go labels Jul 26, 2021
This was referenced Jul 26, 2021
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@kvark kvark self-assigned this Jul 27, 2021
@kvark kvark mentioned this issue Jul 27, 2021
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bors bot added a commit that referenced this issue Jul 27, 2021
@bors @kvark
Merge #1731
3ee4b60 
1731: hal/dx12: support base vertex/instance r=cwfitzgerald a=kvark

**Connections**
Fixes #1725
Depends on gfx-rs/naga#1141, gfx-rs/d3d12-rs#34, and gfx-rs/d3d12-rs#35 (thanks `@msiglreith` for quick reviews!).

**Description**
We allocate one root parameter covering the special constant buffer view with root constants. We set the root constants for each draw, but only on change.

This PR does *not* handle the indirect case. I'll follow-up with this.

**Testing**
Not thoroughly tested, but `@cwfitzgerald` already implemented a test for this, and this PR enables it on DX12.
Also, examples still seem to work :)


Co-authored-by: Dzmitry Malyshau <kvarkus@gmail.com>
@bors bors bot closed this as completed in 2940347 Jul 27, 2021
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hal/dx12: support base vertex/instance kvark/wgpu
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