Vulkan-Docs/appendices/VK_NV_compute_shader_deriva...

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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