C Specification

As part of coverage reduction, fragment color values can also be modulated (multiplied) by a value that is a function of fraction of covered rasterization samples associated with that color sample.

Pipeline state controlling coverage modulation is specified through the members of the VkPipelineCoverageModulationStateCreateInfoNV structure.

The VkPipelineCoverageModulationStateCreateInfoNV structure is defined as:

// Provided by VK_NV_framebuffer_mixed_samples
typedef struct VkPipelineCoverageModulationStateCreateInfoNV {
    VkStructureType                                   sType;
    const void*                                       pNext;
    VkPipelineCoverageModulationStateCreateFlagsNV    flags;
    VkCoverageModulationModeNV                        coverageModulationMode;
    VkBool32                                          coverageModulationTableEnable;
    uint32_t                                          coverageModulationTableCount;
    const float*                                      pCoverageModulationTable;
} VkPipelineCoverageModulationStateCreateInfoNV;

Members

  • sType is a VkStructureType value identifying this structure.

  • pNext is NULL or a pointer to a structure extending this structure.

  • flags is reserved for future use.

  • coverageModulationMode is a VkCoverageModulationModeNV value controlling which color components are modulated.

  • coverageModulationTableEnable controls whether the modulation factor is looked up from a table in pCoverageModulationTable.

  • coverageModulationTableCount is the number of elements in pCoverageModulationTable.

  • pCoverageModulationTable is a table of modulation factors containing a value for each number of covered samples.

Description

If coverageModulationTableEnable is VK_FALSE, then for each color sample the associated bits of the pixel coverage are counted and divided by the number of associated bits to produce a modulation factor R in the range (0,1] (a value of zero would have been killed due to a color coverage of 0). Specifically:

  • N = value of rasterizationSamples

  • M = value of VkAttachmentDescription::samples for any color attachments

  • R = popcount(associated coverage bits) / (N / M)

If coverageModulationTableEnable is VK_TRUE, the value R is computed using a programmable lookup table. The lookup table has N / M elements, and the element of the table is selected by:

  • R = pCoverageModulationTable[popcount(associated coverage bits)-1]

Note that the table does not have an entry for popcount(associated coverage bits) = 0, because such samples would have been killed.

The values of pCoverageModulationTable may be rounded to an implementation-dependent precision, which is at least as fine as 1 / N, and clamped to [0,1].

For each color attachment with a floating point or normalized color format, each fragment output color value is replicated to M values which can each be modulated (multiplied) by that color sample’s associated value of R. Which components are modulated is controlled by coverageModulationMode.

If this structure is not included in the pNext chain, it is as if coverageModulationMode is VK_COVERAGE_MODULATION_MODE_NONE_NV.

If the coverage reduction mode is VK_COVERAGE_REDUCTION_MODE_TRUNCATE_NV, each color sample is associated with only a single coverage sample. In this case, it is as if coverageModulationMode is VK_COVERAGE_MODULATION_MODE_NONE_NV.

Valid Usage

  • VUID-VkPipelineCoverageModulationStateCreateInfoNV-coverageModulationTableEnable-01405
    If coverageModulationTableEnable is VK_TRUE, coverageModulationTableCount must be equal to the number of rasterization samples divided by the number of color samples in the subpass

Valid Usage (Implicit)

  • VUID-VkPipelineCoverageModulationStateCreateInfoNV-sType-sType
    sType must be VK_STRUCTURE_TYPE_PIPELINE_COVERAGE_MODULATION_STATE_CREATE_INFO_NV

  • VUID-VkPipelineCoverageModulationStateCreateInfoNV-flags-zerobitmask
    flags must be 0

  • VUID-VkPipelineCoverageModulationStateCreateInfoNV-coverageModulationMode-parameter
    coverageModulationMode must be a valid VkCoverageModulationModeNV value

See Also

VK_NV_framebuffer_mixed_samples, VkBool32, VkCoverageModulationModeNV, VkPipelineCoverageModulationStateCreateFlagsNV, VkStructureType

Document Notes

For more information, see the Vulkan Specification

This page is extracted from the Vulkan Specification. Fixes and changes should be made to the Specification, not directly.

Copyright

Copyright 2014-2024 The Khronos Group Inc.

SPDX-License-Identifier: CC-BY-4.0