KhronosGroup / KhronosGroup/Vulkan-Portability
Request change to Vulkan spec regarding multiViewport feature tied to geometry shaders?
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- Forks
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Description
Metal supports multiple viewports, and MoltenVK enables the `multiViewport` feature, as it [can be useful for `VK_EXT_shader_viewport_index_layer`](https://github.com/KhronosGroup/MoltenVK/issues/1356#issuecomment-834861082).
However, doing so actually violates the Vulkan and SPIR-V specs, which require `multiViewport` to be enabled only if `geometryShader` is enabled, which Metal does not support. CTS enforces that restriction in test `dEQP-VK.info.device_features`.
Per the suggestion by @cdavis5e in the link above, one option might be to request that Vulkan and SPIR-V loosen this general restriction.
Contributor guide
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Research direction
Start with the issue's linked MoltenVK discussion and the Vulkan and SPIR-V restrictions it cites. Review CTS test dEQP-VK.info.device_features to understand the enforced relationship between multiViewport and geometryShader. Done would require resolving the proposed specification change with the relevant standards projects.
Written by the indexing model from the issue text.
Assessment
- Domain
- computer-graphics
- Issue type
- Feature
- Difficulty
- 5/5
- Estimated time
- Over a week
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 25/100