VK_EXT_legacy_dithering

Other Extension Metadata

Last Modified Date

2024-02-22

Contributors

Shahbaz Youssefi, Google
Graeme Leese, Broadcom
Jan-Harald Fredriksen, Arm

This extension exposes a hardware feature used by some vendors to implement OpenGL’s dithering. The purpose of this extension is to support layering OpenGL over Vulkan, by allowing the layer to take advantage of the same hardware feature and provide equivalent dithering to OpenGL applications.

New Structures

Extending VkPhysicalDeviceFeatures2, VkDeviceCreateInfo:
- VkPhysicalDeviceLegacyDitheringFeaturesEXT

New Enum Constants

VK_EXT_LEGACY_DITHERING_EXTENSION_NAME
VK_EXT_LEGACY_DITHERING_SPEC_VERSION
Extending VkStructureType:
- VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_LEGACY_DITHERING_FEATURES_EXT
Extending VkSubpassDescriptionFlagBits:
- VK_SUBPASS_DESCRIPTION_ENABLE_LEGACY_DITHERING_BIT_EXT

If VK_KHR_dynamic_rendering or Vulkan Version 1.3 and VK_KHR_maintenance5 is supported:

Extending VkPipelineCreateFlagBits2KHR:
- VK_PIPELINE_CREATE_2_ENABLE_LEGACY_DITHERING_BIT_EXT
Extending VkRenderingFlagBits:
- VK_RENDERING_ENABLE_LEGACY_DITHERING_BIT_EXT

Version History

Revision 1, 2022-03-31 (Shahbaz Youssefi)
- Internal revisions
Revision 2, 2024-02-22 (Shahbaz Youssefi)
- Added pipeline create flag to support dynamic rendering

Issues

1) In OpenGL, the dither state can change dynamically. Should this extension add a pipeline state for dither?

RESOLVED: No. Changing dither state is rarely, if ever, done during rendering. Every surveyed Android application either entirely disables dither, explicitly enables it, or uses the default state (which is enabled). Additionally, on some hardware dither can only be specified in a render pass granularity, so a change in dither state would necessarily need to cause a render pass break. This extension considers dynamic changes in OpenGL dither state a theoretical situation, and expects the layer to break the render pass in such a situation without any practical downsides.