Vulkan-Docs/appendices/VK_KHR_shader_draw_paramete...

110 lines
3.3 KiB
Plaintext

// Copyright (c) 2016-2019 Khronos Group. This work is licensed under a
// Creative Commons Attribution 4.0 International License; see
// http://creativecommons.org/licenses/by/4.0/
include::meta/VK_KHR_shader_draw_parameters.txt[]
*Last Modified Date*::
2017-09-05
*IP Status*::
No known IP claims.
*Interactions and External Dependencies*::
- Requires the
https://www.khronos.org/registry/spir-v/extensions/KHR/SPV_KHR_shader_draw_parameters.html[`SPV_KHR_shader_draw_parameters`]
SPIR-V extension.
- Requires
https://www.khronos.org/registry/OpenGL/extensions/ARB/ARB_shader_draw_parameters.txt[`GL_ARB_shader_draw_parameters`]
for GLSL source languages.
- Promoted to Vulkan 1.1 Core
*Contributors*::
- Daniel Koch, NVIDIA Corporation
- Jeff Bolz, NVIDIA
- Daniel Rakos, AMD
- Jan-Harald Fredriksen, ARM
- John Kessenich, Google
- Stuart Smith, IMG
This extension adds support for the following SPIR-V extension in Vulkan:
* `SPV_KHR_shader_draw_parameters`
The extension provides access to three additional built-in shader variables
in Vulkan:
* code:BaseInstance, which contains the pname:firstInstance parameter
passed to draw commands,
* code:BaseVertex, which contains the pname:firstVertex/pname:vertexOffset
parameter passed to draw commands, and
* code:DrawIndex, which contains the index of the draw call currently
being processed from an indirect draw call.
When using GLSL source-based shader languages, the following variables from
`GL_ARB_shader_draw_parameters` can map to these SPIR-V built-in
decorations:
* `in int gl_BaseInstanceARB;` -> code:BaseInstance,
* `in int gl_BaseVertexARB;` -> code:BaseVertex, and
* `in int gl_DrawIDARB;` -> code:DrawIndex.
=== New Object Types
None.
=== New Enum Constants
None.
=== New Enums
None.
=== New Structures
None.
=== New Functions
None.
=== New Built-In Variables
* <<interfaces-builtin-variables-baseinstance,code:BaseInstance>>
* <<interfaces-builtin-variables-basevertex,code:BaseVertex>>
* <<interfaces-builtin-variables-drawindex,code:DrawIndex>>
=== New SPIR-V Capabilities
* <<spirvenv-capabilities,DrawParameters>>
=== Promotion to Vulkan 1.1
All functionality in this extension is included in core Vulkan 1.1, however
a <<features-shaderDrawParameters,feature bit was added>> to distinguish
whether it's actually available or not.
=== Issues
1) Is this the same functionality as `GL_ARB_shader_draw_parameters`?
*RESOLVED*: It's actually a superset as it also adds in support for arrayed
drawing commands.
In GL for `GL_ARB_shader_draw_parameters`, code:gl_BaseVertexARB holds the
integer value passed to the parameter to the command that resulted in the
current shader invocation.
In the case where the command has no code:baseVertex parameter, the value of
code:gl_BaseVertexARB is zero.
This means that code:gl_BaseVertexARB = code:baseVertex (for
code:glDrawElements commands with code:baseVertex) or 0.
In particular there are no code:glDrawArrays commands that take a
code:baseVertex parameter.
Now in Vulkan, we have code:BaseVertex = pname:vertexOffset (for indexed
drawing commands) or pname:firstVertex (for arrayed drawing commands), and
so Vulkan's version is really a superset of GL functionality.
=== Version History
* Revision 1, 2016-10-05 (Daniel Koch)
- Internal revisions