text: /*
   * Copyright 2015 Google Inc.
   *
   * Use of this source code is governed by a BSD-style license that can be
   * found in the LICENSE file.
   */
  
  #include "effects/GrCustomXfermode.h"
  
  #include "GrCoordTransform.h"
  #include "GrContext.h"
  #include "GrFragmentProcessor.h"
  #include "GrInvariantOutput.h"
  #include "GrPipeline.h"
  #include "GrProcessor.h"
  #include "GrTexture.h"
  #include "GrTextureAccess.h"
  #include "SkXfermode.h"
  #include "glsl/GrGLSLBlend.h"
  #include "glsl/GrGLSLCaps.h"
  #include "glsl/GrGLSLFragmentProcessor.h"
  #include "glsl/GrGLSLFragmentShaderBuilder.h"
  #include "glsl/GrGLSLProgramBuilder.h"
  #include "glsl/GrGLSLProgramDataManager.h"
  #include "glsl/GrGLSLXferProcessor.h"
  
  bool GrCustomXfermode::IsSupportedMode(SkXfermode::Mode mode) {
      return mode > SkXfermode::kLastCoeffMode && mode <= SkXfermode::kLastMode;
  }
  
  ///////////////////////////////////////////////////////////////////////////////
  // Static helpers
  ///////////////////////////////////////////////////////////////////////////////
  
  static GrBlendEquation hw_blend_equation(SkXfermode::Mode mode) {
      enum { kOffset = kOverlay_GrBlendEquation - SkXfermode::kOverlay_Mode };
      return static_cast<GrBlendEquation>(mode + kOffset);
  
      GR_STATIC_ASSERT(kOverlay_GrBlendEquation == SkXfermode::kOverlay_Mode + kOffset);
      GR_STATIC_ASSERT(kDarken_GrBlendEquation == SkXfermode::kDarken_Mode + kOffset);
      GR_STATIC_ASSERT(kLighten_GrBlendEquation == SkXfermode::kLighten_Mode + kOffset);
      GR_STATIC_ASSERT(kColorDodge_GrBlendEquation == SkXfermode::kColorDodge_Mode + kOffset);
      GR_STATIC_ASSERT(kColorBurn_GrBlendEquation == SkXfermode::kColorBurn_Mode + kOffset);
      GR_STATIC_ASSERT(kHardLight_GrBlendEquation == SkXfermode::kHardLight_Mode + kOffset);
      GR_STATIC_ASSERT(kSoftLight_GrBlendEquation == SkXfermode::kSoftLight_Mode + kOffset);
      GR_STATIC_ASSERT(kDifference_GrBlendEquation == SkXfermode::kDifference_Mode + kOffset);
      GR_STATIC_ASSERT(kExclusion_GrBlendEquation == SkXfermode::kExclusion_Mode + kOffset);
      GR_STATIC_ASSERT(kMultiply_GrBlendEquation == SkXfermode::kMultiply_Mode + kOffset);
      GR_STATIC_ASSERT(kHSLHue_GrBlendEquation == SkXfermode::kHue_Mode + kOffset);
      GR_STATIC_ASSERT(kHSLSaturation_GrBlendEquation == SkXfermode::kSaturation_Mode + kOffset);
      GR_STATIC_ASSERT(kHSLColor_GrBlendEquation == SkXfermode::kColor_Mode + kOffset);
      GR_STATIC_ASSERT(kHSLLuminosity_GrBlendEquation == SkXfermode::kLuminosity_Mode + kOffset);
      GR_STATIC_ASSERT(kGrBlendEquationCnt == SkXfermode::kLastMode + 1 + kOffset);
  }
  
  static bool can_use_hw_blend_equation(GrBlendEquation equation,
                                        const GrProcOptInfo& coveragePOI,
                                        const GrCaps& caps) {
      if (!caps.advancedBlendEquationSupport()) {
          return false;
      }
      if (coveragePOI.isFourChannelOutput()) {
          return false; // LCD coverage must be applied after the blend equation.
      }
      if (caps.canUseAdvancedBlendEquation(equation)) {
          return false;
      }
      return true;
  }
  
  ///////////////////////////////////////////////////////////////////////////////
  // Xfer Processor
  ///////////////////////////////////////////////////////////////////////////////
  
  class CustomXP : public GrXferProcessor {
  public:
      CustomXP(SkXfermode::Mode mode, GrBlendEquation hwBlendEquation)
          : fMode(mode),
            fHWBlendEquation(hwBlendEquation) {
          this->initClassID<CustomXP>();
      }
  
      CustomXP(const DstTexture* dstTexture, bool hasMixedSamples, SkXfermode::Mode mode)
          : INHERITED(dstTexture, true, hasMixedSamples),
            fMode(mode),
            fHWBlendEquation(static_cast<GrBlendEquation>(-1)) {
          this->initClassID<CustomXP>();
      }
  
      const char* name() const override { return "Custom Xfermode"; }
  
      GrGLSLXferProcessor* createGLSLInstance() const override;
  
      SkXfermode::Mode mode() const { return fMode; }
      bool hasHWBlendEquation() const { return -1 != static_cast<int>(fHWBlendEquation); }
  
      GrBlendEquation hwBlendEquation() const {
          SkASSERT(this->hasHWBlendEquation());
          return fHWBlendEquation;
      }
  
  private:
      GrXferProcessor::OptFlags onGetOptimizations(const GrPipelineOptimizations& optimizations,
                                                   bool doesStencilWrite,
                                                   GrColor* overrideColor,
                                                   const GrCaps& caps) const override;
  
      void onGetGLSLProcessorKey(const GrGLSLCaps& caps, GrProcessorKeyBuilder* b) const override;
  
      GrXferBarrierType onXferBarrier(const GrRenderTarget*, const GrCaps&) const override;
  
      void onGetBlendInfo(BlendInfo*) const override;
  
      bool onIsEqual(const GrXferProcessor& xpBase) const override;
  
      const SkXfermode::Mode fMode;
      const GrBlendEquation  fHWBlendEquation;
  
      typedef GrXferProcessor INHERITED;
  };
  
  ///////////////////////////////////////////////////////////////////////////////
  
  class GLCustomXP : public GrGLSLXferProcessor {
  public:
      GLCustomXP(const GrXferProcessor&) {}
      ~GLCustomXP() override {}
  
      static void GenKey(const GrXferProcessor& p, const GrGLSLCaps& caps, GrProcessorKeyBuilder* b) {
          const CustomXP& xp = p.cast<CustomXP>();
          uint32_t key = 0;
          if (xp.hasHWBlendEquation()) {
              SkASSERT(caps.advBlendEqInteraction() > 0);  // 0 will mean !xp.hasHWBlendEquation().
              key |= caps.advBlendEqInteraction();
              GR_STATIC_ASSERT(GrGLSLCaps::kLast_AdvBlendEqInteraction < 4);
          }
          if (!xp.hasHWBlendEquation() || caps.mustEnableSpecificAdvBlendEqs()) {
              key |= xp.mode() << 3;
          }
          b->add32(key);
      }
  
  private:
      void emitOutputsForBlendState(const EmitArgs& args) override {
          const CustomXP& xp = args.fXP.cast<CustomXP>();
          SkASSERT(xp.hasHWBlendEquation());
  
          GrGLSLXPFragmentBuilder* fragBuilder = args.fXPFragBuilder;
          fragBuilder->enableAdvancedBlendEquationIfNeeded(xp.hwBlendEquation());
  
          // Apply coverage by multiplying it into the src color before blending. Mixed samples will
          // "just work" automatically. (See onGetOptimizations())
          if (args.fInputCoverage) {
              fragBuilder->codeAppendf("%s = %s * %s;",
                                       args.fOutputPrimary, args.fInputCoverage, args.fInputColor);
          } else {
              fragBuilder->codeAppendf("%s = %s;", args.fOutputPrimary, args.fInputColor);
          }
      }
  
      void emitBlendCodeForDstRead(GrGLSLXPBuilder* pb,
                                   GrGLSLXPFragmentBuilder* fragBuilder,
                                   const char* srcColor,
                                   const char* srcCoverage,
                                   const char* dstColor,
                                   const char* outColor,
                                   const char* outColorSecondary,
                                   const GrXferProcessor& proc) override {
          const CustomXP& xp = proc.cast<CustomXP>();
          SkASSERT(!xp.hasHWBlendEquation());
  
          GrGLSLBlend::AppendMode(fragBuilder, srcColor, dstColor, outColor, xp.mode());
  
          // Apply coverage.
          if (xp.dstReadUsesMixedSamples()) {
              if (srcCoverage) {
                  fragBuilder->codeAppendf("%s *= %s;", outColor, srcCoverage);
                  fragBuilder->codeAppendf("%s = %s;", outColorSecondary, srcCoverage);
              } else {
                  fragBuilder->codeAppendf("%s = vec4(1.0);", outColorSecondary);
              }
          } else if (srcCoverage) {
              fragBuilder->codeAppendf("%s = %s * %s + (vec4(1.0) - %s) * %s;",
                                       outColor, srcCoverage, outColor, srcCoverage, dstColor);
          }
      }
  
      void onSetData(const GrGLSLProgramDataManager&, const GrXferProcessor&) override {}
  
      typedef GrGLSLXferProcessor INHERITED;
  };
  
  ///////////////////////////////////////////////////////////////////////////////
  
  void CustomXP::onGetGLSLProcessorKey(const GrGLSLCaps& caps, GrProcessorKeyBuilder* b) const {
      GLCustomXP::GenKey(*this, caps, b);
  }
  
  GrGLSLXferProcessor* CustomXP::createGLSLInstance() const {
      SkASSERT(this->willReadDstColor() != this->hasHWBlendEquation());
      return new GLCustomXP(*this);
  }
  
  bool CustomXP::onIsEqual(const GrXferProcessor& other) const {
      const CustomXP& s = other.cast<CustomXP>();
      return fMode == s.fMode && fHWBlendEquation == s.fHWBlendEquation;
  }
  
  GrXferProcessor::OptFlags CustomXP::onGetOptimizations(const GrPipelineOptimizations& optimizations,
                                                         bool doesStencilWrite,
                                                         GrColor* overrideColor,
                                                         const GrCaps& caps) const {
    /*
      Most the optimizations we do here are based on tweaking alpha for coverage.
  
      The general SVG blend equation is defined in the spec as follows:
  
        Dca' = B(Sc, Dc) * Sa * Da + Y * Sca * (1-Da) + Z * Dca * (1-Sa)
        Da'  = X * Sa * Da + Y * Sa * (1-Da) + Z * Da * (1-Sa)
  
      (Note that Sca, Dca indicate RGB vectors that are premultiplied by alpha,
       and that B(Sc, Dc) is a mode-specific function that accepts non-multiplied
       RGB colors.)
  
      For every blend mode supported by this class, i.e. the "advanced" blend
      modes, X=Y=Z=1 and this equation reduces to the PDF blend equation.
  
      It can be shown that when X=Y=Z=1, these equations can modulate alpha for
      coverage.
  
  
      == Color ==
  
      We substitute Y=Z=1 and define a blend() function that calculates Dca' in
      terms of premultiplied alpha only:
  
        blend(Sca, Dca, Sa, Da) = {Dca : if Sa == 0,
                                   Sca : if Da == 0,
                                   B(Sca/Sa, Dca/Da) * Sa * Da + Sca * (1-Da) + Dca * (1-Sa) : if Sa,Da != 0}
  
      And for coverage modulation, we use a post blend src-over model:
  
        Dca'' = f * blend(Sca, Dca, Sa, Da) + (1-f) * Dca
  
      (Where f is the fractional coverage.)
  
      Next we show that canTweakAlphaForCoverage() is true by proving the
      following relationship:
  
        blend(f*Sca, Dca, f*Sa, Da) == f * blend(Sca, Dca, Sa, Da) + (1-f) * Dca
  
      General case (f,Sa,Da != 0):
  
        f * blend(Sca, Dca, Sa, Da) + (1-f) * Dca
          = f * (B(Sca/Sa, Dca/Da) * Sa * Da + Sca * (1-Da) + Dca * (1-Sa)) + (1-f) * Dca  [Sa,Da != 0, definition of blend()]
          = B(Sca/Sa, Dca/Da) * f*Sa * Da + f*Sca * (1-Da) + f*Dca * (1-Sa) + Dca - f*Dca
          = B(Sca/Sa, Dca/Da) * f*Sa * Da + f*Sca - f*Sca * Da + f*Dca - f*Dca * Sa + Dca - f*Dca
          = B(Sca/Sa, Dca/Da) * f*Sa * Da + f*Sca - f*Sca * Da - f*Dca * Sa + Dca
          = B(Sca/Sa, Dca/Da) * f*Sa * Da + f*Sca * (1-Da) - f*Dca * Sa + Dca
          = B(Sca/Sa, Dca/Da) * f*Sa * Da + f*Sca * (1-Da) + Dca * (1 - f*Sa)
          = B(f*Sca/f*Sa, Dca/Da) * f*Sa * Da + f*Sca * (1-Da) + Dca * (1 - f*Sa)  [f!=0]
          = blend(f*Sca, Dca, f*Sa, Da)  [definition of blend()]
  
      Corner cases (Sa=0, Da=0, and f=0):
  
        Sa=0: f * blend(Sca, Dca, Sa, Da) + (1-f) * Dca
                = f * Dca + (1-f) * Dca  [Sa=0, definition of blend()]
                = Dca
                = blend(0, Dca, 0, Da)  [definition of blend()]
                = blend(f*Sca, Dca, f*Sa, Da)  [Sa=0]
  
        Da=0: f * blend(Sca, Dca, Sa, Da) + (1-f) * Dca
                = f * Sca + (1-f) * Dca  [Da=0, definition of blend()]
                = f * Sca  [Da=0]
                = blend(f*Sca, 0, f*Sa, 0)  [definition of blend()]
                = blend(f*Sca, Dca, f*Sa, Da)  [Da=0]
  
        f=0: f * blend(Sca, Dca, Sa, Da) + (1-f) * Dca
               = Dca  [f=0]
               = blend(0, Dca, 0, Da)  [definition of blend()]
               = blend(f*Sca, Dca, f*Sa, Da)  [f=0]
  
      == Alpha ==
  
      We substitute X=Y=Z=1 and define a blend() function that calculates Da':
  
        blend(Sa, Da) = Sa * Da + Sa * (1-Da) + Da * (1-Sa)
                      = Sa * Da + Sa - Sa * Da + Da - Da * Sa
                      = Sa + Da - Sa * Da
  
      We use the same model for coverage modulation as we did with color:
  
        Da'' = f * blend(Sa, Da) + (1-f) * Da
  
      And show that canTweakAlphaForCoverage() is true by proving the following
      relationship:
  
        blend(f*Sa, Da) == f * blend(Sa, Da) + (1-f) * Da
  
  
        f * blend(Sa, Da) + (1-f) * Da
          = f * (Sa + Da - Sa * Da) + (1-f) * Da
          = f*Sa + f*Da - f*Sa * Da + Da - f*Da
          = f*Sa - f*Sa * Da + Da
          = f*Sa + Da - f*Sa * Da
          = blend(f*Sa, Da)
     */
  
      OptFlags flags = kNone_OptFlags;
      if (optimizations.fColorPOI.allStagesMultiplyInput()) {
          flags |= kCanTweakAlphaForCoverage_OptFlag;
      }
      if (this->hasHWBlendEquation() && optimizations.fCoveragePOI.isSolidWhite()) {
          flags |= kIgnoreCoverage_OptFlag;
      }
      return flags;
  }
  
  GrXferBarrierType CustomXP::onXferBarrier(const GrRenderTarget* rt, const GrCaps& caps) const {
      if (this->hasHWBlendEquation() && !caps.advancedCoherentBlendEquationSupport()) {
          return kBlend_GrXferBarrierType;
      }
      return kNone_GrXferBarrierType;
  }
  
  void CustomXP::onGetBlendInfo(BlendInfo* blendInfo) const {
      if (this->hasHWBlendEquation()) {
          blendInfo->fEquation = this->hwBlendEquation();
      }
  }
  
  ///////////////////////////////////////////////////////////////////////////////
  class CustomXPFactory : public GrXPFactory {
  public:
      CustomXPFactory(SkXfermode::Mode mode);
  
      void getInvariantBlendedColor(const GrProcOptInfo& colorPOI,
                                    GrXPFactory::InvariantBlendedColor*) const override;
  
  private:
      GrXferProcessor* onCreateXferProcessor(const GrCaps& caps,
                                             const GrPipelineOptimizations& optimizations,
                                             bool hasMixedSamples,
                                             const DstTexture*) const override;
  
      bool willReadDstColor(const GrCaps& caps,
                            const GrPipelineOptimizations& optimizations,
                            bool hasMixedSamples) const override;
  
      bool onIsEqual(const GrXPFactory& xpfBase) const override {
          const CustomXPFactory& xpf = xpfBase.cast<CustomXPFactory>();
          return fMode == xpf.fMode;
      }
  
      GR_DECLARE_XP_FACTORY_TEST;
  
      SkXfermode::Mode fMode;
      GrBlendEquation  fHWBlendEquation;
  
      typedef GrXPFactory INHERITED;
  };
  
  CustomXPFactory::CustomXPFactory(SkXfermode::Mode mode)
      : fMode(mode),
        fHWBlendEquation(hw_blend_equation(mode)) {
      SkASSERT(GrCustomXfermode::IsSupportedMode(fMode));
      this->initClassID<CustomXPFactory>();
  }
  
  GrXferProcessor* CustomXPFactory::onCreateXferProcessor(const GrCaps& caps,
                                                          const GrPipelineOptimizations& opt,
                                                          bool hasMixedSamples,
                                                          const DstTexture* dstTexture) const {
      if (can_use_hw_blend_equation(fHWBlendEquation, opt.fCoveragePOI, caps)) {
          SkASSERT(!dstTexture || !dstTexture->texture());
          return new CustomXP(fMode, fHWBlendEquation);
      }
      return new CustomXP(dstTexture, hasMixedSamples, fMode);
  }
  
  bool CustomXPFactory::willReadDstColor(const GrCaps& caps,
                                         const GrPipelineOptimizations& optimizations,
                                         bool hasMixedSamples) const {
      return !can_use_hw_blend_equation(fHWBlendEquation, optimizations.fCoveragePOI, caps);
  }
  
  void CustomXPFactory::getInvariantBlendedColor(const GrProcOptInfo& colorPOI,
                                                 InvariantBlendedColor* blendedColor) const {
      blendedColor->fWillBlendWithDst = true;
      blendedColor->fKnownColorFlags = kNone_GrColorComponentFlags;
  }
  
  GR_DEFINE_XP_FACTORY_TEST(CustomXPFactory);
  const GrXPFactory* CustomXPFactory::TestCreate(GrProcessorTestData* d) {
      int mode = d->fRandom->nextRangeU(SkXfermode::kLastCoeffMode + 1,
                                        SkXfermode::kLastSeparableMode);
  
      return new CustomXPFactory(static_cast<SkXfermode::Mode>(mode));
  }
  
  ///////////////////////////////////////////////////////////////////////////////
  
  GrXPFactory* GrCustomXfermode::CreateXPFactory(SkXfermode::Mode mode) {
      if (!GrCustomXfermode::IsSupportedMode(mode)) {
          return nullptr;
      } else {
          return new CustomXPFactory(mode);
      }
  }
  