Required Vulkan Spec Documentation Modifications

[billhollings]

This is a list of Vulkan modifications for portability that can be accomplished through changes to the Vulkan spec documentation, without requiring the need for additional feature flags or values. Typically, this applies to the loosening of required features or formats, or of required numerical limits.

Vulkan spec wording and VU's would be adjusted to include wording similar to:

If the VK_KHR_portability_subset extension is enabled, this feature/format is not required.

If the VK_KHR_portability_subset extension is enabled, the required limit is nnnn.

Such changes also require changes to the appropriate CTS test in order to apply the adjusted requirements. In each entry here, the CTS Tests Affected is listed for investigative purposes. A single issue may actually affect multiple CTS tests, and all may not be listed here if the expectation is that fixing one should fix them all.

Description	Vulkan spec	Portability spec	CTS Tests Affected	Status
VkPhysicalDeviceLimits:: maxSamplerAllocationCount	Min 4000 required	1024	dEQP-VK.info.device_properties
VK_FORMAT_B4G4R4A4_UNORM_PACK16 VK_FORMAT_R5G6B5_UNORM_PACK16 VK_FORMAT_A1R5G5B5_UNORM_PACK16	Requires minimal VkFormatFeatureFlags	Not required	dEQP-VK.api.info.format_properties.b4g4r4a4_unorm_pack16 dEQP-VK.api.info.format_properties.r5g6b5_unorm_pack16 dEQP-VK.api.info.format_properties.a1r5g5b5_unorm_pack16 dEQP-VK.texture.explicit_lod.2d.formats.b4g4r4a4_unorm_pack16_nearest dEQP-VK.texture.explicit_lod.2d.formats.b4g4r4a4_unorm_pack16_linear
VK_FORMAT_R32_UINT VK_FORMAT_R32_SINT	VK_FORMAT_FEATURE_STORAGE_IMAGE_ATOMIC_BIT required in optimalTilingFeatures	Not required	dEQP-VK.api.info.format_properties.r32_uint dEQP-VK.api.info.format_properties.r32_sint
On some platforms, primitive restart cannot always be disabled	VkPipelineInputAssemblyStateCreateInfo.primitiveRestartEnable and vkCmdSetPrimitiveRestartEnableEXT() can be set to VK_FALSE	VkPipelineInputAssemblyStateCreateInfo.primitiveRestartEnable and vkCmdSetPrimitiveRestartEnableEXT() must always be set to VK_TRUE	None. All CTS primitive restart tests only test enabling.
VkVertexInputBindingDescription::stride must be a multiple of 4	VkVertexInputBindingDescription::stride can be any value	VkVertexInputBindingDescription::stride must be a multiple of 4 (see also #30 re zero value)	CTS tests currently using VkPhysicalDevicePortabilitySubsetPropertiesKHR::minVertexInputBindingStrideAlignment should macro-define a fixed value (currently known to be 4) .
Vulkan prohibits multiViewport without geometry shaders but Metal does not (see #23)	multiViewport prohibited without geometry shaders	multiViewport allowed for other uses without geometry shaders in main spec, with or without VK_KHR_portability subset	dEQP-VK.info.device_features

[billhollings]

Need to submit these spec changes to the WG.

[lexaknyazev]

VkPipelineInputAssemblyStateCreateInfo.primitiveRestartEnable and vkCmdSetPrimitiveRestartEnableEXT() must always be set to VK_TRUE.

This should say

... must always be set to VK_TRUE for triangle strip and line strip topology types.

[billhollings]

... must always be set to VK_TRUE for triangle strip and line strip topology types.

I didn't include this, because the spec includes the following, which would be disabled:

Primitive restart is not allowed for “list” topologies, unless one of the features primitiveTopologyPatchListRestart (for VK_PRIMITIVE_TOPOLOGY_PATCH_LIST) or primitiveTopologyListRestart (for all other list topologies) is enabled.

However, I guess the extra clarifying text doesn't hurt.