Deprecation state
-
Promoted to Vulkan 1.1
Other Extension Metadata
- Last Modified Date
-
2017-09-05
- IP Status
-
No known IP claims.
- Interactions and External Dependencies
-
-
This extension requires
SPV_KHR_shader_draw_parameters
-
This extension provides API support for
GL_ARB_shader_draw_parameters
-
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
-
Description
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:
-
BaseInstance
, which contains thefirstInstance
parameter passed to draw commands, -
BaseVertex
, which contains thefirstVertex
orvertexOffset
parameter passed to draw commands, and -
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;
→BaseInstance
, -
in int gl_BaseVertexARB;
→BaseVertex
, and -
in int gl_DrawIDARB;
→DrawIndex
.
Promotion to Vulkan 1.1
All functionality in this extension is included in core Vulkan 1.1, however a feature bit was added to distinguish whether it is actually available or not.
New Enum Constants
-
VK_KHR_SHADER_DRAW_PARAMETERS_EXTENSION_NAME
-
VK_KHR_SHADER_DRAW_PARAMETERS_SPEC_VERSION
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
, 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 baseVertex
parameter, the value of
gl_BaseVertexARB
is zero.
This means that gl_BaseVertexARB
= baseVertex
(for
glDrawElements
commands with baseVertex
) or 0.
In particular there are no glDrawArrays
commands that take a
baseVertex
parameter.
Now in Vulkan, we have BaseVertex
= vertexOffset
(for indexed
drawing commands) or firstVertex
(for arrayed drawing commands), and
so Vulkan’s version is really a superset of GL functionality.
Document Notes
For more information, see the Vulkan Specification
This page is a generated document. Fixes and changes should be made to the generator scripts, not directly.