VK_EXT_shader_subgroup_ballot(3)

# VK_EXT_shader_subgroup_ballot(3) Manual Page

## Name

VK_EXT_shader_subgroup_ballot - device extension

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## Registered Extension Number

65

## Revision

1

## Extension and Version Dependencies

- Requires Vulkan 1.0

## Deprecation state

- Deprecated by Vulkan 1.2

## Contact

- Daniel Koch dgkoch

## Other Extension Metadata

Last Modified Date

  2016-11-28

IP Status

  No known IP claims.

Interactions and External Dependencies

  - This extension requires `SPV_KHR_shader_ballot`

  - This extension provides API support for `GL_ARB_shader_ballot`

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 a invocation value, or broadcast of a bitarray 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

- `SubgroupEqMaskKHR`

- `SubgroupGeMaskKHR`

- `SubgroupGtMaskKHR`

- `SubgroupLeMaskKHR`

- `SubgroupLtMaskKHR`

- `SubgroupLocalInvocationId`

- `SubgroupSize`

## New SPIR-V Capabilities

- SubgroupBallotKHR

## Version History

- Revision 1, 2016-11-28 (Daniel Koch)

  - Initial draft

## See Also

No cross-references are available

## Document Notes

For more information, see the Vulkan Specification

This page is a generated document. Fixes and changes should be made to the generator scripts, not directly.

## Copyright

Copyright 2014-2022 The Khronos Group Inc.

SPDX-License-Identifier: CC-BY-4.0