kc3-lang/angle/src/compiler/translator/TranslatorMetal.cpp

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• Hash : 4cef8a49
  Author :
  Date : 2019-11-26T00:04:00
  

  Metal: Support depthRange near > far
  
  Metal doesn't natively support near > far depthRange, need to
  emulate it via shader.
  
  Bug: angleproject:2634
  Change-Id: I1885cad3467478a0dcc4b25b7d41f980b9e03103
  Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1919282
  Commit-Queue: Jamie Madill <jmadill@chromium.org>
  Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
  

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• src/compiler/translator/TranslatorMetal.cpp

• //
  // Copyright (c) 2019 The ANGLE Project Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  //
  // TranslatorMetal:
  //   A GLSL-based translator that outputs shaders that fit GL_KHR_vulkan_glsl.
  //   It takes into account some considerations for Metal backend also.
  //   The shaders are then fed into glslang to spit out SPIR-V (libANGLE-side).
  //   See: https://www.khronos.org/registry/vulkan/specs/misc/GL_KHR_vulkan_glsl.txt
  //
  //   The SPIR-V will then be translated to Metal Shading Language later in Metal backend.
  //
  
  #include "compiler/translator/TranslatorMetal.h"
  
  #include "angle_gl.h"
  #include "common/utilities.h"
  #include "compiler/translator/OutputVulkanGLSLForMetal.h"
  #include "compiler/translator/StaticType.h"
  #include "compiler/translator/tree_util/BuiltIn.h"
  #include "compiler/translator/tree_util/RunAtTheEndOfShader.h"
  #include "compiler/translator/util.h"
  
  namespace sh
  {
  
  namespace
  {
  
  // Unlike Vulkan having auto viewport flipping extension, in Metal we have to flip gl_Position.y
  // manually.
  // This operation performs flipping the gl_Position.y using this expression:
  // gl_Position.y = gl_Position.y * negViewportScaleY
  ANGLE_NO_DISCARD bool AppendVertexShaderPositionYCorrectionToMain(TCompiler *compiler,
                                                                    TIntermBlock *root,
                                                                    TSymbolTable *symbolTable,
                                                                    TIntermBinary *negViewportYScale)
  {
      // Create a symbol reference to "gl_Position"
      const TVariable *position  = BuiltInVariable::gl_Position();
      TIntermSymbol *positionRef = new TIntermSymbol(position);
  
      // Create a swizzle to "gl_Position.y"
      TVector<int> swizzleOffsetY;
      swizzleOffsetY.push_back(1);
      TIntermSwizzle *positionY = new TIntermSwizzle(positionRef, swizzleOffsetY);
  
      // Create the expression "gl_Position.y * negViewportScaleY"
      TIntermBinary *inverseY = new TIntermBinary(EOpMul, positionY->deepCopy(), negViewportYScale);
  
      // Create the assignment "gl_Position.y = gl_Position.y * negViewportScaleY
      TIntermTyped *positionYLHS = positionY->deepCopy();
      TIntermBinary *assignment  = new TIntermBinary(TOperator::EOpAssign, positionYLHS, inverseY);
  
      // Append the assignment as a statement at the end of the shader.
      return RunAtTheEndOfShader(compiler, root, assignment, symbolTable);
  }
  
  }  // anonymous namespace
  
  TranslatorMetal::TranslatorMetal(sh::GLenum type, ShShaderSpec spec) : TranslatorVulkan(type, spec)
  {}
  
  bool TranslatorMetal::translate(TIntermBlock *root,
                                  ShCompileOptions compileOptions,
                                  PerformanceDiagnostics *perfDiagnostics)
  {
      TInfoSinkBase &sink = getInfoSink().obj;
      TOutputVulkanGLSL outputGLSL(sink, getArrayIndexClampingStrategy(), getHashFunction(),
                                   getNameMap(), &getSymbolTable(), getShaderType(),
                                   getShaderVersion(), getOutputType(), compileOptions);
  
      const TVariable *driverUniforms = nullptr;
      if (!TranslatorVulkan::translateImpl(root, compileOptions, perfDiagnostics, &driverUniforms,
                                           &outputGLSL))
      {
          return false;
      }
  
      if (getShaderType() == GL_VERTEX_SHADER)
      {
          auto negViewportYScale = getDriverUniformNegViewportYScaleRef(driverUniforms);
  
          // Append gl_Position.y correction to main
          if (!AppendVertexShaderPositionYCorrectionToMain(this, root, &getSymbolTable(),
                                                           negViewportYScale))
          {
              return false;
          }
      }
  
      // Write translated shader.
      root->traverse(&outputGLSL);
  
      return true;
  }
  
  // Metal needs to inverse the depth if depthRange is is reverse order, i.e. depth near > depth far
  // This is achieved by multiply the depth value with scale value stored in
  // driver uniform's depthRange.reserved
  bool TranslatorMetal::transformDepthBeforeCorrection(TIntermBlock *root,
                                                       const TVariable *driverUniforms)
  {
      // Create a symbol reference to "gl_Position"
      const TVariable *position  = BuiltInVariable::gl_Position();
      TIntermSymbol *positionRef = new TIntermSymbol(position);
  
      // Create a swizzle to "gl_Position.z"
      TVector<int> swizzleOffsetZ = {2};
      TIntermSwizzle *positionZ   = new TIntermSwizzle(positionRef, swizzleOffsetZ);
  
      // Create a ref to "depthRange.reserved"
      TIntermBinary *viewportZScale = getDriverUniformDepthRangeReservedFieldRef(driverUniforms);
  
      // Create the expression "gl_Position.z * depthRange.reserved".
      TIntermBinary *zScale = new TIntermBinary(EOpMul, positionZ->deepCopy(), viewportZScale);
  
      // Create the assignment "gl_Position.z = gl_Position.z * depthRange.reserved"
      TIntermTyped *positionZLHS = positionZ->deepCopy();
      TIntermBinary *assignment  = new TIntermBinary(TOperator::EOpAssign, positionZLHS, zScale);
  
      // Append the assignment as a statement at the end of the shader.
      return RunAtTheEndOfShader(this, root, assignment, &getSymbolTable());
  }
  
  }  // namespace sh
  

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