[[VK_NVX_multiview_per_view_attributes]]
== VK_NVX_multiview_per_view_attributes

*Name String*::
    +VK_NVX_multiview_per_view_attributes+
*Extension Type*::
    Device extension
*Registered Extension Number*::
    98
*Status*::
    Draft.
*Last Modified Date*::
    2017-01-13
*Revision*::
    1
*IP Status*::
    No known IP claims.
*Dependencies*::
  - This extension is written against version 1.0 of the Vulkan API.
  - This extension requires the
    https://www.khronos.org/registry/spir-v/extensions/NV/SPV_NVX_multiview_per_view_attributes.html[+SPV_NVX_multiview_per_view_attributes+]
    SPIR-V extension.
  - This extension requires the +GL_NVX_multiview_per_view_attributes+
    extension for GLSL source languages.
  - Requires
    <<VK_KHR_get_physical_device_properties2,VK_KHR_get_physical_device_properties2>>
    and <<VK_KHX_multiview,VK_KHX_multiview>>.
  - This extension interacts with
    <<VK_NV_viewport_array2,VK_NV_viewport_array2>>.
*Contributors*::
  - Jeff Bolz, NVIDIA
  - Daniel Koch, NVIDIA
*Contacts*::
  - Jeff Bolz (jbolz 'at' nvidia.com)
*Overview*::
+
--
This extension adds a new way to write shaders to be used with multiview
subpasses, where the attributes for all views are written out by a single
invocation of the vertex processing stages.
Related SPIR-V and GLSL extensions +SPV_NVX_multiview_per_view_attributes+
and +GL_NVX_multiview_per_view_attributes+ introduce per-view position and
viewport mask attributes arrays, and this extension defines how those
per-view attribute arrays are interpreted by Vulkan.
Pipelines using per-view attributes may: only execute the vertex processing
stages once for all views rather than once per-view, which reduces redundant
shading work.

A subpass creation flag controls whether the subpass uses this extension.
A subpass must: either exclusively use this extension or not use it at all.

Some Vulkan implementations only support the position attribute varying
between views in the X component.
A subpass can declare via a second creation flag whether all pipelines
compiled for this subpass will obey this restriction.

Shaders that use the new per-view outputs (e.g. gl_PositionPerViewNV) must:
also write the non-per-view output (gl_Position), and the values written
must: be such that gl_Position = gl_PositionPerViewNV[gl_ViewIndex] for all
views in the subpass.
Implementations are free to either use the per-view outputs or the
non-per-view outputs, whichever would be more efficient.

If +VK_NV_viewport_array2+ is not also supported and enabled, the per-view
viewport mask must: not be used.
--

=== New Object Types

None.

=== New Enum Constants

  * Extending ename:VkStructureType
  ** ename:VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_MULTIVIEW_PER_VIEW_ATTRIBUTES_PROPERTIES_NVX

  * Extending ename:VkSubpassDescriptionFlagBits
  ** ename:VK_SUBPASS_DESCRIPTION_PER_VIEW_ATTRIBUTES_BIT_NVX
  ** ename:VK_SUBPASS_DESCRIPTION_PER_VIEW_POSITION_X_ONLY_BIT_NVX

=== New Enums

None.

=== New Structures

  * slink:VkPhysicalDeviceMultiviewPerViewAttributesPropertiesNVX

=== New Functions

None.

=== New Built-In Variables
  * <<interfaces-builtin-variables-positionperview,code:PositionPerViewNV>>
  * <<interfaces-builtin-variables-viewportmaskperview,code:ViewportMaskPerViewNV>>

=== New SPIR-V Capabilities
  * <<spirvenv-capabilities-table-perviewattributes,code:PerViewAttributesNV>>

=== Issues

None.

=== Examples

[source,c]
---------------------------------------------------
#version 450 core

#extension GL_KHX_multiview : enable
#extension GL_NVX_multiview_per_view_attributes : enable

layout(location = 0) in vec4 position;
layout(set = 0, binding = 0) uniform Block { mat4 mvpPerView[2]; } buf;

void main()
{
    // Output both per-view positions and gl_Position as a function
    // of gl_ViewIndex
    gl_PositionPerViewNV[0] = buf.mvpPerView[0] * position;
    gl_PositionPerViewNV[1] = buf.mvpPerView[1] * position;
    gl_Position = buf.mvpPerView[gl_ViewIndex] * position;
}

---------------------------------------------------


=== Version History

 * Revision 1, 2017-01-13 (Jeff Bolz)
   - Internal revisions
