kc3-lang/angle/src/libANGLE/renderer/vulkan/doc/ShaderModuleCompilation.md

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• Author : Le Quyen
  Date : 2019-10-14 14:49:49
  Hash : a48f95ab
  Message : Move Vulkan GlslangWrapper code to a shared location. Metal backend will reuse Vulkan's GlslangWrapper code. The Metal backend will use this code to translate glsl to spirv then cross compile to Metal Shading Language using spirv-cross. So the source code of GlslangWrapper should be moved outside vulkan folder. Bug: angleproject:2634 Change-Id: I208062daf0d77756c9d32cfdab925b7dfdf83e05 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1858042 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>

• src/libANGLE/renderer/vulkan/doc/ShaderModuleCompilation.md

• # Shader Module Compilation
  
  ANGLE converts application shaders into Vulkan [VkShaderModules][VkShaderModule] through a series
  of steps:
  
  1. **ANGLE Internal Translation**: The initial calls to `glCompileShader` are passed to the [ANGLE
  shader translator][translator]. The translator compiles application shaders into Vulkan-compatible
  GLSL. Vulkan-compatible GLSL matches the [GL_KHR_vulkan_glsl][GL_KHR_vulkan_glsl] extension spec
  with some additional workarounds and emulation. We emulate OpenGL's different depth range, viewport
  y flipping, default uniforms, and OpenGL [line segment
  rasterization](OpenGLLineSegmentRasterization.md). For more info see
  [TranslatorVulkan.cpp][TranslatorVulkan.cpp]. After initial compilation the shaders are not
  complete. They are templated with markers that are filled in later at link time.
  
  1. **Link-Time Translation**: During a call to `glLinkProgram` the Vulkan back-end can know the
  necessary locations and properties to write to connect the shader stage interfaces. We get the
  completed shader source using ANGLE's [GlslangWrapperVk][GlslangWrapperVk.cpp] helper class. We still
  cannot generate `VkShaderModules` since some ANGLE features like [OpenGL line
  rasterization](OpenGLLineSegmentRasterization.md) emulation depend on draw-time information.
  
  1. **Draw-time SPIR-V Generation**: Once the application records a draw call we use Khronos'
  [glslang][glslang] to convert the Vulkan-compatible GLSL into SPIR-V with the correct draw-time
  defines. The SPIR-V is then compiled into `VkShaderModules`. For details please see
  [GlslangWrapperVk.cpp][GlslangWrapperVk.cpp]. The `VkShaderModules` are then used by `VkPipelines`. Note
  that we currently don't use [SPIRV-Tools][SPIRV-Tools] to perform any SPIR-V optimization. This
  could be something to improve on in the future.
  
  See the below diagram for a high-level view of the shader translation flow:
  
  <!-- Generated from https://bramp.github.io/js-sequence-diagrams/
  participant App
  participant "ANGLE Front-end"
  participant "Vulkan Back-end"
  participant "ANGLE Translator"
  participant "GlslangWrapperVk"
  participant "Glslang"
  
  App->"ANGLE Front-end": glCompileShader (VS)
  "ANGLE Front-end"->"Vulkan Back-end": ShaderVk::compile
  "Vulkan Back-end"->"ANGLE Translator": sh::Compile
  "ANGLE Translator"- ->"ANGLE Front-end": return Vulkan-compatible GLSL
  
  Note right of "ANGLE Front-end": Source is templated\nwith markers to be\nfilled at link time.
  
  Note right of App: Same for FS, GS, etc...
  
  App->"ANGLE Front-end": glCreateProgram (...)
  App->"ANGLE Front-end": glAttachShader (...)
  App->"ANGLE Front-end": glLinkProgram
  "ANGLE Front-end"->"Vulkan Back-end": ProgramVk::link
  
  Note right of "Vulkan Back-end": ProgramVk inits uniforms,\nlayouts, and descriptors.
  
  "Vulkan Back-end"->GlslangWrapperVk: GlslangWrapperVk::GetShaderSource
  GlslangWrapperVk- ->"Vulkan Back-end": return filled-in sources
  
  Note right of "Vulkan Back-end": Source is templated with\ndefines to be resolved at\ndraw time.
  
  "Vulkan Back-end"- ->"ANGLE Front-end": return success
  
  Note right of App: App execution continues...
  
  App->"ANGLE Front-end": glDrawArrays (any draw)
  "ANGLE Front-end"->"Vulkan Back-end": ContextVk::drawArrays
  
  "Vulkan Back-end"->GlslangWrapperVk: GlslangWrapperVk::GetShaderCode (with defines)
  GlslangWrapperVk->Glslang: GlslangToSpv
  Glslang- ->"Vulkan Back-end": Return SPIR-V
  
  Note right of "Vulkan Back-end": We init VkShaderModules\nand VkPipeline then\nrecord the draw.
  
  "Vulkan Back-end"- ->"ANGLE Front-end": return success
  -->
  
  ![Vulkan Shader Translation Flow](https://raw.githubusercontent.com/google/angle/master/src/libANGLE/renderer/vulkan/doc/img/VulkanShaderTranslation.svg?sanitize=true)
  
  [GL_KHR_vulkan_glsl]: https://github.com/KhronosGroup/GLSL/blob/master/extensions/khr/GL_KHR_vulkan_glsl.txt
  [glslang]: https://github.com/KhronosGroup/glslang
  [GlslangWrapperVk.cpp]: https://chromium.googlesource.com/angle/angle/+/refs/heads/master/src/libANGLE/renderer/vulkan/GlslangWrapperVk.cpp
  [SPIRV-Tools]: https://github.com/KhronosGroup/SPIRV-Tools
  [translator]: https://chromium.googlesource.com/angle/angle/+/refs/heads/master/src/compiler/translator/
  [TranslatorVulkan.cpp]: https://chromium.googlesource.com/angle/angle/+/refs/heads/master/src/compiler/translator/TranslatorVulkan.cpp
  [VkShaderModule]: https://www.khronos.org/registry/vulkan/specs/1.1-extensions/man/html/VkShaderModule.html