third_party/angle/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