# VertexIndex(3) Manual Page

## Name

VertexIndex - Vertex index of a shader invocation

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## Description

`VertexIndex`

  Decorating a variable with the `VertexIndex` built-in decoration will make that variable contain the index of the vertex that is being processed by the current vertex shader invocation. For non-indexed draws, this variable begins at the `firstVertex` parameter to vkCmdDraw or the `firstVertex` member of a structure consumed by vkCmdDrawIndirect and increments by one for each vertex in the draw. For indexed draws, its value is the content of the index buffer for the vertex plus the `vertexOffset` parameter to vkCmdDrawIndexed or the `vertexOffset` member of the structure consumed by vkCmdDrawIndexedIndirect.

Note | `VertexIndex` starts at the same starting value for each instance.

Valid Usage

- VUID-VertexIndex-VertexIndex-04398
  The `VertexIndex` decoration must be used only within the `Vertex` `Execution` `Model`

- VUID-VertexIndex-VertexIndex-04399
  The variable decorated with `VertexIndex` must be declared using the `Input` `Storage` `Class`

- VUID-VertexIndex-VertexIndex-04400
  The variable decorated with `VertexIndex` must be declared as a scalar 32-bit integer value

## See Also

No cross-references are available

## Document Notes

For more information, see the Vulkan Specification

This page is extracted from the Vulkan Specification. Fixes and changes should be made to the Specification, not directly.

## Copyright

Copyright 2014-2024 The Khronos Group Inc.

SPDX-License-Identifier: CC-BY-4.0