kc3-lang/angle/src/libANGLE/renderer/vulkan/doc/ShaderModuleCompilation.md
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Hash : 2682b5a0
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Date : 2019-10-07T15:13:23
Documentation maintenance. Fixes links in the Vulkan back-end doc. Also includes a link to the Vulkan back-end docs on the main page. Also updates the building code section to mention VS2019 and make the win toolchain varable set more prominent. Bug: angleproject:1944 Change-Id: I8e8f0775daa3643afaa1ddd44429fa7d8e77b19b Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1846014 Reviewed-by: Jamie Madill <jmadill@chromium.org>
Shader Module Compilation
ANGLE converts application shaders into Vulkan VkShaderModules through a series of steps:
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ANGLE Internal Translation: The initial calls to
glCompileShaderare passed to the ANGLE shader translator. The translator compiles application shaders into Vulkan-compatible GLSL. Vulkan-compatible GLSL matches the 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. For more info see TranslatorVulkan.cpp. After initial compilation the shaders are not complete. They are templated with markers that are filled in later at link time. -
Link-Time Translation: During a call to
glLinkProgramthe 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 GlslangWrapper helper class. We still cannot generateVkShaderModulessince some ANGLE features like OpenGL line rasterization emulation depend on draw-time information. -
Draw-time SPIR-V Generation: Once the application records a draw call we use Khronos’ 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 GlslangWrapper.cpp. TheVkShaderModulesare then used byVkPipelines. Note that we currently don’t use 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:
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src/libANGLE/renderer/vulkan/doc/ShaderModuleCompilation.md
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# 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 [GlslangWrapper][GlslangWrapper.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 [GlslangWrapper.cpp][GlslangWrapper.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 "GlslangWrapper" 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"->GlslangWrapper: GlslangWrapper::GetShaderSource GlslangWrapper- ->"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"->GlslangWrapper: GlslangWrapper::GetShaderCode (with defines) GlslangWrapper->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 -->  [GL_KHR_vulkan_glsl]: https://github.com/KhronosGroup/GLSL/blob/master/extensions/khr/GL_KHR_vulkan_glsl.txt [glslang]: https://github.com/KhronosGroup/glslang [GlslangWrapper.cpp]: https://chromium.googlesource.com/angle/angle/+/refs/heads/master/src/libANGLE/renderer/vulkan/GlslangWrapper.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