VK_EXT_fragment_density_map

Other Extension Metadata

Last Modified Date

2021-09-30

Interactions and External Dependencies

This extension provides API support for GL_EXT_fragment_invocation_density

Contributors

Matthew Netsch, Qualcomm Technologies, Inc.
Robert VanReenen, Qualcomm Technologies, Inc.
Jonathan Wicks, Qualcomm Technologies, Inc.
Tate Hornbeck, Qualcomm Technologies, Inc.
Sam Holmes, Qualcomm Technologies, Inc.
Jeff Leger, Qualcomm Technologies, Inc.
Jan-Harald Fredriksen, ARM
Jeff Bolz, NVIDIA
Pat Brown, NVIDIA
Daniel Rakos, AMD
Piers Daniell, NVIDIA

This extension allows an application to specify areas of the render target where the fragment shader may be invoked fewer times. These fragments are broadcasted out to multiple pixels to cover the render target.

The primary use of this extension is to reduce workloads in areas where lower quality may not be perceived such as the distorted edges of a lens or the periphery of a user’s gaze.

New Structures

If Vulkan Version 1.3 or VK_KHR_dynamic_rendering is supported:

Extending VkRenderingInfo:
- VkRenderingFragmentDensityMapAttachmentInfoEXT

New Enum Constants

VK_EXT_FRAGMENT_DENSITY_MAP_EXTENSION_NAME
VK_EXT_FRAGMENT_DENSITY_MAP_SPEC_VERSION
Extending VkAccessFlagBits:
- VK_ACCESS_FRAGMENT_DENSITY_MAP_READ_BIT_EXT
Extending VkFormatFeatureFlagBits:
- VK_FORMAT_FEATURE_FRAGMENT_DENSITY_MAP_BIT_EXT
Extending VkImageCreateFlagBits:
- VK_IMAGE_CREATE_SUBSAMPLED_BIT_EXT
Extending VkImageLayout:
- VK_IMAGE_LAYOUT_FRAGMENT_DENSITY_MAP_OPTIMAL_EXT
Extending VkImageUsageFlagBits:
- VK_IMAGE_USAGE_FRAGMENT_DENSITY_MAP_BIT_EXT
Extending VkImageViewCreateFlagBits:
- VK_IMAGE_VIEW_CREATE_FRAGMENT_DENSITY_MAP_DYNAMIC_BIT_EXT
Extending VkPipelineStageFlagBits:
- VK_PIPELINE_STAGE_FRAGMENT_DENSITY_PROCESS_BIT_EXT
Extending VkSamplerCreateFlagBits:
- VK_SAMPLER_CREATE_SUBSAMPLED_BIT_EXT
- VK_SAMPLER_CREATE_SUBSAMPLED_COARSE_RECONSTRUCTION_BIT_EXT
Extending VkStructureType:
- VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_FRAGMENT_DENSITY_MAP_FEATURES_EXT
- VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_FRAGMENT_DENSITY_MAP_PROPERTIES_EXT
- VK_STRUCTURE_TYPE_RENDER_PASS_FRAGMENT_DENSITY_MAP_CREATE_INFO_EXT

If VK_KHR_format_feature_flags2 or Vulkan Version 1.3 is supported:

Extending VkFormatFeatureFlagBits2:
- VK_FORMAT_FEATURE_2_FRAGMENT_DENSITY_MAP_BIT_EXT

If Vulkan Version 1.3 or VK_KHR_dynamic_rendering is supported:

Extending VkPipelineCreateFlagBits:
- VK_PIPELINE_CREATE_RENDERING_FRAGMENT_DENSITY_MAP_ATTACHMENT_BIT_EXT
- VK_PIPELINE_RASTERIZATION_STATE_CREATE_FRAGMENT_DENSITY_MAP_ATTACHMENT_BIT_EXT
Extending VkStructureType:
- VK_STRUCTURE_TYPE_RENDERING_FRAGMENT_DENSITY_MAP_ATTACHMENT_INFO_EXT

New or Modified Built-In Variables

New SPIR-V Capabilities

FragmentDensityEXT

Examples

Fragment Density Map

An image can be bound as a fragment density map attachment to a render pass. This image contains normalized (x, y) float component fragment density values for regions of the framebuffer that will be used in rasterization for every subpass. A float component ranges from (0.0, 1.0] where 1.0 means full density along that axis. Implementations use these values as hints to optimize rendering in areas of low density. Subpass color and depth attachments can be created as subsampled, which can help to further optimize rendering in areas of low density.

The density map image can be modified by the application until calling vkCmdBeginRenderPass for the render pass that uses the image. If VK_IMAGE_VIEW_CREATE_FRAGMENT_DENSITY_MAP_DYNAMIC_BIT_EXT is used, then the application can modify the image until the device reads it during VK_PIPELINE_STAGE_FRAGMENT_DENSITY_PROCESS_BIT_EXT.

// Create fragment density map
VkImageCreateInfo imageCreateInfo =
{
   .sType = VK_STRUCTURE_TYPE_IMAGE_CREATE_INFO,
   .pNext = nullptr,
   .flags = 0,
   .imageType = VK_IMAGE_TYPE_2D,    // Must be 2D
   .format = VK_FORMAT_R8G8_UNORM,   // Must have VK_FORMAT_FEATURE_FRAGMENT_DENSITY_MAP_BIT_EXT
   .extend = {64, 64, 1},
   .mipLevels = 1,
   .arrayLayers = 2,                 // 1 for each multiview view
   .samples = VK_SAMPLE_COUNT_1_BIT, // Must be 1x MSAA
   .tiling = tiling,
   .usage = VK_IMAGE_USAGE_FRAGMENT_DENSITY_MAP_BIT_EXT,
   // ...
};

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

VkImageViewCreateInfo viewCreateInfo =
{
   .sType = VK_STRUCTURE_TYPE_IMAGE_VIEW_CREATE_INFO,
   .pNext = nullptr,
   .flags = 0,                      // VkImageViewCreateFlags
   .image = fdmImage,
   .viewType = VK_IMAGE_VIEW_TYPE_2D_ARRAY,
   .format = VK_FORMAT_R8G8_UNORM,
   .components = { 0 },             // VK_COMPONENT_SWIZZLE_IDENTITY
   .subresourceRange = {
        .aspectMask = VK_IMAGE_ASPECT_COLOR_BIT,
        .baseMipLevel = 0,
        .levelCount = 1,
        .baseArrayLayer = 0,
        .layerCount = 2,
   }
};

vkCreateImageView(device, &viewCreateInfo, nullptr, &fdmImageView);

// Add fdmImage to render pass

VkAttachmentReference fragmentDensityMapAttachmentReference =
{
   fdmAttachmentIdx,
   VK_IMAGE_LAYOUT_FRAGMENT_DENSITY_MAP_OPTIMAL_EXT,
};

VkRenderPassFragmentDensityMapCreateInfoEXT fdmAttachmentCreateInfo =
{
   VK_STRUCTURE_TYPE_RENDER_PASS_FRAGMENT_DENSITY_MAP_CREATE_INFO_EXT,
   // ...
   fragmentDensityMapAttachmentReference,
};

VkRenderPassCreateInfo2 renderPassCreateInfo =
{
   VK_STRUCTURE_TYPE_RENDER_PASS_CREATE_INFO_2,
   &fdmAttachmentCreateInfo,
   // ...
};

vkCreateRenderPass2(device, &renderPassCreateInfo, nullptr, &renderPass);

// Add fdmImage to framebuffer
// Color attachments can be created with VK_IMAGE_CREATE_SUBSAMPLED_BIT_EXT
// All attachments must be created with VK_IMAGE_CREATE_FRAGMENT_DENSITY_MAP_OFFSETS_BIT_EXT
VkFramebufferCreateInfo framebufferCreateInfo =
{
   .sType = VK_STRUCTURE_TYPE_FRAME_BUFFER_CREATE_INFO,
   // ...
   .renderPass = renderPass,
   // ...
   .pAttachments = pAttachments, // Includes fdmImageView at fdmAttachmentIdx
   .width = 1024,
   .height = 1024,
   .layers = 1
};

vkCreateFramebuffer(device, &framebufferCreateInfo, nullptr, &framebuffer);

// Start recording render pass in command buffer

VkRenderPassBeginInfo renderPassBeginInfo =
{
   .sType = VK_STRUCTURE_TYPE_RENDER_PASS_BEGIN_INFO,
   // ...
   .renderPass = renderPass,
   .framebuffer = framebuffer,
   // ...
};

// Can no longer modify the fdmImage's contents after this call
vkCmdBeginRenderPass2(commandBuffer, &renderPassBeginInfo, pSubpassBeginInfo);

Version History

Revision 1, 2018-09-25 (Matthew Netsch)
- Initial version
Revision 2, 2021-09-30 (Jon Leech)
- Add interaction with VK_KHR_format_feature_flags2 to vk.xml