include::meta/VK_EXT_shader_viewport_index_layer.txt[]

*Last Modified Date*::
    2017-08-08
*Interactions and External Dependencies*::
  - This extension requires the
    https://www.khronos.org/registry/spir-v/extensions/EXT/SPV_EXT_shader_viewport_index_layer.html[+SPV_EXT_shader_viewport_index_layer+]
    SPIR-V extension.
  - This extension requires the
    https://www.khronos.org/registry/OpenGL/extensions/ARB/ARB_shader_viewport_layer_array.txt[+GL_ARB_shader_viewport_layer_array+],
    https://www.khronos.org/registry/OpenGL/extensions/AMD/AMD_vertex_shader_layer.txt[+GL_AMD_vertex_shader_layer+],
    https://www.khronos.org/registry/OpenGL/extensions/AMD/AMD_vertex_shader_viewport_index.txt[+GL_AMD_vertex_shader_viewport_index+],
    or
    https://www.khronos.org/registry/OpenGL/extensions/NV/NV_viewport_array2.txt[+GL_NV_viewport_array2+]
    extensions for GLSL source languages.
  - This extension requires the pname:multiViewport feature.
  - This extension interacts with the pname:tessellationShader feature.
*Contributors*::
  - Piers Daniell, NVIDIA
  - Jeff Bolz, NVIDIA
  - Jan-Harald Fredriksen, ARM
  - Daniel Rakos, AMD
  - Slawomir Grajeswki, Intel

This extension adds support for the code:ShaderViewportIndexLayerEXT
capability from the +SPV_EXT_shader_viewport_index_layer+ extension in
Vulkan.

This extension allows variables decorated with the code:Layer and
code:ViewportIndex built-ins to be exported from vertex or tessellation
shaders, using the code:ShaderViewportIndexLayerEXT capability.

When using GLSL source-based shading languages, the code:gl_ViewportIndex
and code:gl_Layer built-in variables map to the SPIR-V code:ViewportIndex
and code:Layer built-in decorations, respectively.
Behaviour of these variables is extended as described in the
+GL_ARB_shader_viewport_layer_array+ (or the precursor
+GL_AMD_vertex_shader_layer+, +GL_AMD_vertex_shader_viewport_index+, and
+GL_NV_viewport_array2 extensions+).

ifdef::VK_NV_viewport_array2[]
[NOTE]
.Note
====
The code:ShaderViewportIndexLayerEXT capability is equivalent to the
code:ShaderViewportIndexLayerNV capability added by
`<<VK_NV_viewport_array2>>`.
====
endif::VK_NV_viewport_array2[]

=== New Object Types

None.

=== New Enum Constants

None.

=== New Enums

None.

=== New Structures

None.

=== New Functions

None.

=== New or Modified Built-In Variables

  * (modified) <<interfaces-builtin-variables-layer,code:Layer>>
  * (modified)
    <<interfaces-builtin-variables-viewportindex,code:ViewportIndex>>

=== New Variable Decoration

None.

=== New SPIR-V Capabilities

  * <<spirvenv-capabilities-table-shader-viewport-index-layer,code:ShaderViewportIndexLayerEXT>>

=== Issues

None yet!

=== Version History

  * Revision 1, 2017-08-08 (Daniel Koch)
    - Internal drafts