Name

VK_EXT_depth_clip_control - device extension

VK_EXT_depth_clip_control

Name String

VK_EXT_depth_clip_control

Extension Type

Device extension

Registered Extension Number

356

Revision

1

Ratification Status

Not ratified

Extension and Version Dependencies

VK_KHR_get_physical_device_properties2

Special Use

• OpenGL / ES support

Contact

• Shahbaz Youssefi @syoussefi%0A*Here describe the issue or question you have about the VK_EXT_depth_clip_control extension*

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 PhysicalDeviceFeatures2, DeviceCreateInfo:

  • PhysicalDeviceDepthClipControlFeaturesEXT

• Extending PipelineViewportStateCreateInfo:

  • PipelineViewportDepthClipControlCreateInfoEXT

New Enum Constants

• EXT_DEPTH_CLIP_CONTROL_EXTENSION_NAME

• EXT_DEPTH_CLIP_CONTROL_SPEC_VERSION

• Extending StructureType:

  • STRUCTURE_TYPE_PHYSICAL_DEVICE_DEPTH_CLIP_CONTROL_FEATURES_EXT
  • 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 PipelineViewportStateCreateInfo::pNext instead.

Version History

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

  • Internal revisions

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

  • Language fixes

See Also

PhysicalDeviceDepthClipControlFeaturesEXT, PipelineViewportDepthClipControlCreateInfoEXT

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.