Vulkan-Docs/appendices/VK_NV_compute_shader_derivatives.txt

include::meta/VK_NV_compute_shader_derivatives.txt[]

*Last Modified Date*::
    2018-07-19
*IP Status*::
    No known IP claims.
*Contributors*::
  - Pat Brown, NVIDIA

This extension adds Vulkan support for the
`SPV_NV_compute_shader_derivatives` SPIR-V extension.

The SPIR-V extension provides two new execution modes, both of which allow
compute shaders to use built-ins that evaluate compute derivatives
explicitly or implicitly.
Derivatives will be computed via differencing over a 2x2 group of shader
invocations.
The code:DerivativeGroupQuadsNV execution mode assembles shader invocations
into 2x2 groups, where each group has x and y coordinates of the local
invocation ID of the form (2m+{0,1}, 2n+{0,1}).
The code:DerivativeGroupLinearNV execution mode assembles shader invocations
into 2x2 groups, where each group has local invocation index values of the
form 4m+{0,1,2,3}.

=== New Object Types

None.

=== New Enum Constants

  * Extending elink:VkStructureType:
  ** ename:VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_COMPUTE_SHADER_DERIVATIVES_FEATURES_NV

=== New Enums

None.

=== New Structures

  * slink:VkPhysicalDeviceComputeShaderDerivativesFeaturesNV

=== New Functions

None.

=== New SPIR-V Capability

  * <<spirvenv-capabilities-table-computederivatives-quads,ComputeDerivativeGroupQuadsNV>>
  * <<spirvenv-capabilities-table-computederivatives-linear,ComputeDerivativeGroupLinearNV>>

=== Issues

(1) Should we specify that the groups of four shader invocations used for
    derivatives in a compute shader are the same groups of four invocations
    that form a "`quad`" in shader subgroups?

*RESOLVED*: Yes.


=== Examples

None.

=== Version History

 * Revision 1, 2018-07-19 (Pat Brown)
   - Initial draft