include::meta/VK_NV_coverage_reduction_mode.txt[]

*Last Modified Date*::
  2019-01-29
*Contributors*::
  - Kedarnath Thangudu, NVIDIA
  - Jeff Bolz, NVIDIA

When using a framebuffer with mixed samples, a per-fragment coverage
reduction operation is performed which generates a color sample mask from
the coverage mask.
This extension defines the following modes to control how this reduction is
performed.

  * Merge: When there are more raster samples than color samples, there is
    an implementation dependent association of each raster sample to a color
    sample.
    In the merge mode, the reduced color sample mask is computed such that
    the bit for each color sample is 1 if any of the associated bits in the
    fragment’s coverage is on, and 0 otherwise.
    This is the default mode.

  * Truncate: When there are more raster samples (N) than color samples(M),
    there is one to one association of the first M raster samples to the M
    color samples and the coverage bits for the other raster samples are
    ignored.

When the number of raster samples is equal to the color samples, there is a
one to one mapping between them in either of the above modes.

The new command
flink:vkGetPhysicalDeviceSupportedFramebufferMixedSamplesCombinationsNV can
be used to query the various raster, color, depth/stencil sample count and
reduction mode combinations that are supported by the implementation.
This extension would allow an implementation to support the behavior of both
`VK_NV_framebuffer_mixed_samples` and `VK_AMD_mixed_attachment_samples`
extensions simultaneously.


=== New Object Types

None.

=== New Enum Constants

  * Extending elink:VkStructureType
  ** ename:VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_COVERAGE_REDUCTION_MODE_FEATURES_NV
  ** ename:VK_STRUCTURE_TYPE_PIPELINE_COVERAGE_REDUCTION_STATE_CREATE_INFO_NV
  ** ename:VK_STRUCTURE_TYPE_FRAMEBUFFER_MIXED_SAMPLES_COMBINATION_NV

=== New Enums

  * elink:VkCoverageReductionModeNV
  * tlink:VkPipelineCoverageReductionStateCreateFlagsNV

=== New Structures

  * slink:VkPhysicalDeviceCoverageReductionModeFeaturesNV
  * slink:VkPipelineCoverageReductionStateCreateInfoNV
  * slink:VkFramebufferMixedSamplesCombinationNV

=== New Functions

 * flink:vkGetPhysicalDeviceSupportedFramebufferMixedSamplesCombinationsNV

=== Issues

None.

=== Version History

  * Revision 1, 2019-01-29 (Kedarnath Thangudu)
    - Internal revisions