VK_EXT_depth_clip_control(3)

# VK_EXT_depth_clip_control(3) Manual Page

## Name

VK_EXT_depth_clip_control - device extension

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## Registered Extension Number

356

## Revision

1

## Extension and Version Dependencies

VK_KHR_get_physical_device_properties2

## Special Use

- OpenGL / ES support

## Contact

- Shahbaz Youssefi syoussefi

## Other Extension Metadata

Last Modified Date

  2021-11-09

Contributors

  - Spencer Fricke, Samsung Electronics

  - Shahbaz Youssefi, Google

  - Ralph Potter, Samsung Electronics

## Description

This extension allows the application to use the OpenGL depth range in NDC, i.e. with depth in range [-1, 1], as opposed to Vulkan’s default of [0, 1]. The purpose of this extension is to allow efficient layering of OpenGL over Vulkan, by avoiding emulation in the pre-rasterization shader stages. This emulation, which effectively duplicates gl_Position but with a different depth value, costs ALU and consumes shader output components that the implementation may not have to spare to meet OpenGL minimum requirements.

## New Structures

- Extending VkPhysicalDeviceFeatures2, VkDeviceCreateInfo:

  - VkPhysicalDeviceDepthClipControlFeaturesEXT

- Extending VkPipelineViewportStateCreateInfo:

  - VkPipelineViewportDepthClipControlCreateInfoEXT

## New Enum Constants

- `VK_EXT_DEPTH_CLIP_CONTROL_EXTENSION_NAME`

- `VK_EXT_DEPTH_CLIP_CONTROL_SPEC_VERSION`

- Extending VkStructureType:

  - `VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_DEPTH_CLIP_CONTROL_FEATURES_EXT`

  - `VK_STRUCTURE_TYPE_PIPELINE_VIEWPORT_DEPTH_CLIP_CONTROL_CREATE_INFO_EXT`

## Issues

1) Should this extension include an origin control option to match GL_LOWER_LEFT found in ARB_clip_control?

RESOLVED: No. The fix for porting over the origin is a simple y-axis flip. The depth clip control is a much harder problem to solve than what this extension is aimed to solve. Adding an equivalent to GL_LOWER_LEFT would require more testing.

2) Should this pipeline state be dynamic?

RESOLVED: Yes. The purpose of this extension is to emulate the OpenGL depth range, which is expected to be globally fixed (in case of OpenGL ES) or very infrequently changed (with `glClipControl` in OpenGL).

3) Should the control provided in this extension be an enum that could be extended in the future?

RESOLVED: No. It is highly unlikely that the depth range is changed to anything other than [0, 1] in the future. Should that happen a new extension will be required to extend such an enum, and that extension might as well add a new struct to chain to VkPipelineViewportStateCreateInfo::`pNext` instead.

## Version History

- Revision 0, 2020-10-01 (Spencer Fricke)

  - Internal revisions

- Revision 1, 2020-11-26 (Shahbaz Youssefi)

  - Language fixes

## See Also

VkPhysicalDeviceDepthClipControlFeaturesEXT, VkPipelineViewportDepthClipControlCreateInfoEXT

## 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 2014-2023 The Khronos Group Inc.

SPDX-License-Identifier: CC-BY-4.0