117 lines
3.1 KiB
Plaintext
117 lines
3.1 KiB
Plaintext
// Copyright (c) 2016-2017 The Khronos Group Inc.
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// Copyright notice at https://www.khronos.org/registry/speccopyright.html
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[[VK_KHR_shader_draw_parameters]]
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== VK_KHR_shader_draw_parameters
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*Name String*::
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+VK_KHR_shader_draw_parameters+
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*Extension Type*::
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Device extension
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*Registered Extension Number*::
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64
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*Status*::
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Complete
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*Last Modified Data*::
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2016-10-05
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*Revision*::
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1
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*IP Status*::
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No known IP claims.
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*Dependencies*::
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- This extension is written against version 1.0 of the Vulkan API.
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- Requires Vulkan 1.0.
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- Requires the +SPV_KHR_shader_draw_parameters+ SPIR-V extension.
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- Requires +GL_ARB_shader_draw_parameters+ 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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*Contact*::
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- Daniel Koch (dkoch 'at' nvidia.com)
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*Overview*::
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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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+
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--
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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 firstInstance parameter passed to
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draw commands,
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* code:BaseVertex, which contains the firstVertex/vertexOffset parameter
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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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--
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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 baseVertex parameter, the value of
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code:gl_BaseVertexARB is zero.
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This means that code:gl_BaseVertexARB = baseVertex (for code:glDrawElements
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commands with baseVertex) or 0.
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In particular there are no code:glDrawArrays commands that take a baseVertex
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parameter.
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Now in Vulkan, we have *BaseVertex* = _vertexOffset_ (for indexed drawing
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commands) or _firstVertex_ (for arrayed drawing commands), and so Vulkan's
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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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