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VK_EXT_shader_subgroup_ballot

Other Extension Metadata

Last Modified Date

2016-11-28

IP Status

No known IP claims.

Interactions and External Dependencies
Contributors
  • Jeff Bolz, NVIDIA
  • Neil Henning, Codeplay
  • Daniel Koch, NVIDIA Corporation

Description

This extension adds support for the following SPIR-V extension in Vulkan:

  • SPV_KHR_shader_ballot

This extension provides the ability for a group of invocations, which execute in parallel, to do limited forms of cross-invocation communication via a group broadcast of an invocation value, or broadcast of a bit array representing a predicate value from each invocation in the group.

This extension provides access to a number of additional built-in shader variables in Vulkan:

  • SubgroupEqMaskKHR, containing the subgroup mask of the current subgroup invocation,
  • SubgroupGeMaskKHR, containing the subgroup mask of the invocations greater than or equal to the current invocation,
  • SubgroupGtMaskKHR, containing the subgroup mask of the invocations greater than the current invocation,
  • SubgroupLeMaskKHR, containing the subgroup mask of the invocations less than or equal to the current invocation,
  • SubgroupLtMaskKHR, containing the subgroup mask of the invocations less than the current invocation,
  • SubgroupLocalInvocationId, containing the index of an invocation within a subgroup, and
  • SubgroupSize, containing the maximum number of invocations in a subgroup.

Additionally, this extension provides access to the new SPIR-V instructions:

  • OpSubgroupBallotKHR,
  • OpSubgroupFirstInvocationKHR, and
  • OpSubgroupReadInvocationKHR,

When using GLSL source-based shader languages, the following variables and shader functions from GL_ARB_shader_ballot can map to these SPIR-V built-in decorations and instructions:

  • in uint64_t gl_SubGroupEqMaskARB; → SubgroupEqMaskKHR,
  • in uint64_t gl_SubGroupGeMaskARB; → SubgroupGeMaskKHR,
  • in uint64_t gl_SubGroupGtMaskARB; → SubgroupGtMaskKHR,
  • in uint64_t gl_SubGroupLeMaskARB; → SubgroupLeMaskKHR,
  • in uint64_t gl_SubGroupLtMaskARB; → SubgroupLtMaskKHR,
  • in uint gl_SubGroupInvocationARB; → SubgroupLocalInvocationId,
  • uniform uint gl_SubGroupSizeARB; → SubgroupSize,
  • ballotARB() → OpSubgroupBallotKHR,
  • readFirstInvocationARB() → OpSubgroupFirstInvocationKHR, and
  • readInvocationARB() → OpSubgroupReadInvocationKHR.

Deprecated by Vulkan 1.2

Most of the functionality in this extension is superseded by the core Vulkan 1.1 subgroup operations. However, Vulkan 1.1 required the OpGroupNonUniformBroadcast Id to be constant. This restriction was removed in Vulkan 1.2 with the addition of the subgroupBroadcastDynamicId feature.

New Enum Constants

  • VK_EXT_SHADER_SUBGROUP_BALLOT_EXTENSION_NAME
  • VK_EXT_SHADER_SUBGROUP_BALLOT_SPEC_VERSION

New Built-In Variables

New SPIR-V Capabilities

Version History

  • Revision 1, 2016-11-28 (Daniel Koch)
    • Initial draft