VK_EXT_fragment_density_map(3)

# VK_EXT_fragment_density_map(3) Manual Page

## Name

VK_EXT_fragment_density_map - device extension

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## Registered Extension Number

219

## Revision

2

## Extension and Version Dependencies

- Requires support for Vulkan 1.0

- Requires `VK_KHR_get_physical_device_properties2` to be enabled for any device-level functionality

## Contact

- Matthew Netsch mnetsch

## Other Extension Metadata

Last Modified Date

  2021-09-30

Interactions and External Dependencies

  - This extension requires `SPV_EXT_fragment_invocation_density`

  - 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

## Description

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

- Extending VkPhysicalDeviceFeatures2, VkDeviceCreateInfo:

  - VkPhysicalDeviceFragmentDensityMapFeaturesEXT

- Extending VkPhysicalDeviceProperties2:

  - VkPhysicalDeviceFragmentDensityMapPropertiesEXT

- Extending VkRenderPassCreateInfo, VkRenderPassCreateInfo2:

  - VkRenderPassFragmentDensityMapCreateInfoEXT

## 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 is supported:

- Extending VkFormatFeatureFlagBits2:

  - `VK_FORMAT_FEATURE_2_FRAGMENT_DENSITY_MAP_BIT_EXT`

## New or Modified Built-In Variables

- `FragInvocationCountEXT`

- `FragSizeEXT`

## 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 =
    {
       VK_STRUCTURE_TYPE_IMAGE_CREATE_INFO,
       nullptr,
       0,
       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);

    VkImageViewCreateInfo viewCreateInfo =
    {
       VK_STRUCTURE_TYPE_IMAGE_VIEW_CREATE_INFO,
       nullptr,
       0,                          // VkImageViewCreateFlags
       fdmImage,
       VK_IMAGE_VIEW_TYPE_2D_ARRAY,
       VK_FORMAT_R8G8_UNORM,
       {0},                        // VK_COMPONENT_SWIZZLE_IDENTITY
       {VK_IMAGE_ASPECT_COLOR_BIT,
        0,                         // baseMipLevel
        1,                         // levelCount; must be 1
        0,                         // baseArrayLayer
        2,                         // layerCount
       }
    };

    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 =
    {
       VK_STRUCTURE_TYPE_FRAME_BUFFER_CREATE_INFO,
       // ...
       renderPass,
       // ...
       pAttachments, // Includes fdmImageView at fdmAttachmentIdx
       1024,         // width
       1024,         // height
       1             // layers; must be 1 if using multiview
    };

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

    // Start recording render pass in command buffer

    VkRenderPassBeginInfo renderPassBeginInfo =
    {
       VK_STRUCTURE_TYPE_RENDER_PASS_BEGIN_INFO,
       // ...
       renderPass,
       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`

## See Also

VkPhysicalDeviceFragmentDensityMapFeaturesEXT, VkPhysicalDeviceFragmentDensityMapPropertiesEXT, VkRenderPassFragmentDensityMapCreateInfoEXT

## 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 2014-2022 The Khronos Group Inc.

SPDX-License-Identifier: CC-BY-4.0