Registered Extension Number

426

Revision

1

Extension and Version Dependencies

Contact

Other Extension Metadata

Last Modified Date

2021-09-03

Contributors
  • Matthew Netsch, Qualcomm Technologies, Inc.

  • Jonathan Wicks, Qualcomm Technologies, Inc.

  • Jonathan Tinkham, Qualcomm Technologies, Inc.

  • Jeff Leger, Qualcomm Technologies, Inc.

Description

This extension allows an application to specify offsets to a fragment density map attachment, changing the framebuffer location where density values are applied to without having to regenerate the fragment density map.

New Structures

New Enum Constants

  • VK_QCOM_FRAGMENT_DENSITY_MAP_OFFSET_EXTENSION_NAME

  • VK_QCOM_FRAGMENT_DENSITY_MAP_OFFSET_SPEC_VERSION

  • Extending VkImageCreateFlagBits:

    • VK_IMAGE_CREATE_FRAGMENT_DENSITY_MAP_OFFSET_BIT_QCOM

  • Extending VkStructureType:

    • VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_FRAGMENT_DENSITY_MAP_OFFSET_FEATURES_QCOM

    • VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_FRAGMENT_DENSITY_MAP_OFFSET_PROPERTIES_QCOM

    • VK_STRUCTURE_TYPE_SUBPASS_FRAGMENT_DENSITY_MAP_OFFSET_END_INFO_QCOM

Examples

Fragment Density Map

If the fragment density map size is larger than framebuffer size / minFragmentDensityTexelSize, then offsets may be applied with VkSubpassFragmentDensityMapOffsetEndInfoQCOM to shift the framebuffer inside of the density map image. This is helpful if apps want to reuse the same density map image to track content without editing the image.

// Create fragment density map
VkImageCreateInfo imageCreateInfo =
{
   VK_STRUCTURE_TYPE_IMAGE_CREATE_INFO,
   nullptr,
   VK_IMAGE_CREATE_FRAGMENT_DENSITY_MAP_OFFSET_BIT_QCOM,
   VK_IMAGE_TYPE_2D,       // Must be 2D
   VK_FORMAT_R8G8_UNORM,   // Must have VK_FORMAT_FEATURE_FRAGMENT_DENSITY_MAP_BIT_EXT
   {64, 64, 1},            // extent
   1,                      // mipLevels
   2,                      // arrayLayers; 1 for each multiview view
   VK_SAMPLE_COUNT_1_BIT,  // Must be 1x MSAA
   tiling,
   VK_IMAGE_USAGE_FRAGMENT_DENSITY_MAP_BIT_EXT,
   // ...
};

vkCreateImage(device, &imageCreateInfo, nullptr, &fdmImage);

// Start renderpass with fbo that has fdmImage as fragmentDensityMapAttachment
// All other attachments must have been created with
// VK_IMAGE_CREATE_FRAGMENT_DENSITY_MAP_OFFSET_BIT_QCOM
// FBO has dimensions 1024x1024 in this example
vkCmdBeginRenderPass2(commandBuffer, &renderPassBeginInfo, pSubpassBeginInfo);

// ...

// Shift fragment density map image by offset to put fovea in center of vision
/*
   If minFragmentDensityTexelSize is 32x32, then offsets can be at most
   1024x1024 for this example before density value access is clamped to edge of map

   This is because the region of each fdmImage texel is

     texelSize = max(framebuffer / fdmImage, minFragmentDensityTexelSize) = 32x32

   and the fdmImage covers a total framebuffer region of

     fdmImageRegion = fdmImage * texelSize = 2048x2048

   This means that the framebuffer (1024x1024) can be shifted up to 1024x1024
   before the density values are clamped to edge of map
*/
VkSubpassFragmentDensityMapOffsetEndInfoQCOM offsetInfo =
{
   VK_STRUCTURE_TYPE_SUBPASS_FRAGMENT_DENSITY_MAP_OFFSET_END_INFO_QCOM,
   2,             // fragmentDensityOffsetCount; 1 for each layer/multiview view
   offsets,       // offsets are aligned to fragmentDensityOffsetGranularity
};

subpassEndInfo.pNext = &offsetInfo;

// Only offsets given to the last subpass are used for the whole render pass
// Offsets given in other subpasses are ignored
vkCmdEndRenderPass2(VkCommandBuffer commandBuffer, &subpassEndInfo);

Version History

  • Revision 1, 2021-09-03 (Matthew Netsch)

    • Initial version

See Also

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 2014-2022 The Khronos Group Inc.

SPDX-License-Identifier: CC-BY-4.0