103 lines
3.1 KiB
Plaintext
103 lines
3.1 KiB
Plaintext
// Copyright (c) 2016-2018 Khronos Group. This work is licensed under a
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// Creative Commons Attribution 4.0 International License; see
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// http://creativecommons.org/licenses/by/4.0/
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include::meta/VK_KHR_shader_draw_parameters.txt[]
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*Last Modified Date*::
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2016-10-05
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*IP Status*::
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No known IP claims.
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*Interactions and External Dependencies*::
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- Requires the
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https://www.khronos.org/registry/spir-v/extensions/KHR/SPV_KHR_shader_draw_parameters.html[+SPV_KHR_shader_draw_parameters+]
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SPIR-V extension.
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- Requires
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https://www.khronos.org/registry/OpenGL/extensions/ARB/ARB_shader_draw_parameters.txt[+GL_ARB_shader_draw_parameters+]
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for GLSL source languages.
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*Contributors*::
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- Daniel Koch, NVIDIA Corporation
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- Jeff Bolz, NVIDIA
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- Daniel Rakos, AMD
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- Jan-Harald Fredriksen, ARM
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- John Kessenich, Google
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- Stuart Smith, IMG
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This extension adds support for the following SPIR-V extension in Vulkan:
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* +SPV_KHR_shader_draw_parameters+
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The extension provides access to three additional built-in shader variables
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in Vulkan:
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* code:BaseInstance, which contains the pname:firstInstance parameter
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passed to draw commands,
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* code:BaseVertex, which contains the pname:firstVertex/pname:vertexOffset
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parameter passed to draw commands, and
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* code:DrawIndex, which contains the index of the draw call currently
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being processed from an indirect draw call.
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When using GLSL source-based shader languages, the following variables from
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+GL_ARB_shader_draw_parameters+ can map to these SPIR-V built-in
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decorations:
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* `in int gl_BaseInstanceARB;` -> code:BaseInstance,
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* `in int gl_BaseVertexARB;` -> code:BaseVertex, and
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* `in int gl_DrawIDARB;` -> code:DrawIndex.
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=== New Object Types
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None.
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=== New Enum Constants
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None.
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=== New Enums
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None.
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=== New Structures
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None.
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=== New Functions
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None.
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=== New Built-In Variables
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* <<interfaces-builtin-variables-baseinstance,code:BaseInstance>>
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* <<interfaces-builtin-variables-basevertex,code:BaseVertex>>
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* <<interfaces-builtin-variables-drawindex,code:DrawIndex>>
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=== New SPIR-V Capabilities
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* <<spirvenv-capabilities-table-drawparameters,DrawParameters>>
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=== Issues
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1) Is this the same functionality as +GL_ARB_shader_draw_parameters+?
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*RESOLVED*: It's actually a superset as it also adds in support for arrayed
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drawing commands.
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In GL for +GL_ARB_shader_draw_parameters+, code:gl_BaseVertexARB holds the
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integer value passed to the parameter to the command that resulted in the
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current shader invocation.
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In the case where the command has no code:baseVertex parameter, the value of
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code:gl_BaseVertexARB is zero.
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This means that code:gl_BaseVertexARB = code:baseVertex (for
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code:glDrawElements commands with code:baseVertex) or 0.
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In particular there are no code:glDrawArrays commands that take a
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code:baseVertex parameter.
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Now in Vulkan, we have code:BaseVertex = pname:vertexOffset (for indexed
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drawing commands) or pname:firstVertex (for arrayed drawing commands), and
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so Vulkan's version is really a superset of GL functionality.
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=== Version History
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* Revision 1, 2016-10-05 (Daniel Koch)
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- Internal revisions
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