VK_KHR_variable_pointers

Other Extension Metadata

Last Modified Date

2017-09-05

IP Status

No known IP claims.

Contributors

• John Kessenich, Google
• Neil Henning, Codeplay
• David Neto, Google
• Daniel Koch, Nvidia
• Graeme Leese, Broadcom
• Weifeng Zhang, Qualcomm
• Stephen Clarke, Imagination Technologies
• Faith Ekstrand, Intel
• Jesse Hall, Google

Description

The VK_KHR_variable_pointers extension allows implementations to indicate their level of support for the SPV_KHR_variable_pointers SPIR-V extension. The SPIR-V extension allows shader modules to use invocation-private pointers into uniform and/or storage buffers, where the pointer values can be dynamic and non-uniform.

The SPV_KHR_variable_pointers extension introduces two capabilities. The first, VariablePointersStorageBuffer, must be supported by all implementations of this extension. The second, VariablePointers, is optional.

Promotion to Vulkan 1.1

All functionality in this extension is included in core Vulkan 1.1, with the KHR suffix omitted, however support for the variablePointersStorageBuffer feature is made optional. The original type, enum, and command names are still available as aliases of the core functionality.

New Structures

• Extending VkPhysicalDeviceFeatures2, VkDeviceCreateInfo:
  • VkPhysicalDeviceVariablePointerFeaturesKHR
  • VkPhysicalDeviceVariablePointersFeaturesKHR

New Enum Constants

• VK_KHR_VARIABLE_POINTERS_EXTENSION_NAME
• VK_KHR_VARIABLE_POINTERS_SPEC_VERSION
• Extending VkStructureType:
  • VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_VARIABLE_POINTERS_FEATURES_KHR
  • VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_VARIABLE_POINTER_FEATURES_KHR

New SPIR-V Capabilities

• VariablePointers
• VariablePointersStorageBuffer

Issues

1) Do we need an optional property for the SPIR-V VariablePointersStorageBuffer capability or should it be mandatory when this extension is advertised?

RESOLVED: Add it as a distinct feature, but make support mandatory. Adding it as a feature makes the extension easier to include in a future core API version. In the extension, the feature is mandatory, so that presence of the extension guarantees some functionality. When included in a core API version, the feature would be optional.

2) Can support for these capabilities vary between shader stages?

RESOLVED: No, if the capability is supported in any stage it must be supported in all stages.

3) Should the capabilities be features or limits?

RESOLVED: Features, primarily for consistency with other similar extensions.

Version History

• Revision 1, 2017-03-14 (Jesse Hall and John Kessenich)
  • Internal revisions