/*
 * Copyright 2014 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "effects/GrPorterDuffXferProcessor.h"

#include "GrBlend.h"
#include "GrCaps.h"
#include "GrProcessor.h"
#include "GrProcOptInfo.h"
#include "GrTypes.h"
#include "GrXferProcessor.h"
#include "gl/GrGLXferProcessor.h"
#include "gl/builders/GrGLFragmentShaderBuilder.h"
#include "gl/builders/GrGLProgramBuilder.h"

/**
 * Wraps the shader outputs and HW blend state that comprise a Porter Duff blend mode with coverage.
 */
struct BlendFormula {
public:
    /**
     * Values the shader can write to primary and secondary outputs. These must all be modulated by
     * coverage to support mixed samples. The XP will ignore the multiplies when not using coverage.
     */
    enum OutputType {
        kNone_OutputType,        //<! 0
        kCoverage_OutputType,    //<! inputCoverage
        kModulate_OutputType,    //<! inputColor * inputCoverage
        kISAModulate_OutputType, //<! (1 - inputColor.a) * inputCoverage
        kISCModulate_OutputType, //<! (1 - inputColor) * inputCoverage

        kLast_OutputType = kISCModulate_OutputType
    };

    enum Properties {
        kModifiesDst_Property              = 1,
        kUsesDstColor_Property             = 1 << 1,
        kUsesInputColor_Property           = 1 << 2,
        kCanTweakAlphaForCoverage_Property = 1 << 3,

        kLast_Property = kCanTweakAlphaForCoverage_Property
    };

    BlendFormula& operator =(const BlendFormula& other) {
        fData = other.fData;
        return *this;
    }

    bool operator ==(const BlendFormula& other) const {
        return fData == other.fData;
    }

    bool hasSecondaryOutput() const { return kNone_OutputType != fSecondaryOutputType; }
    bool modifiesDst() const { return SkToBool(fProps & kModifiesDst_Property); }
    bool usesDstColor() const { return SkToBool(fProps & kUsesDstColor_Property); }
    bool usesInputColor() const { return SkToBool(fProps & kUsesInputColor_Property); }
    bool canTweakAlphaForCoverage() const {
        return SkToBool(fProps & kCanTweakAlphaForCoverage_Property);
    }

    /**
     * Deduce the properties of a compile-time constant BlendFormula.
     */
    template<OutputType PrimaryOut, OutputType SecondaryOut,
             GrBlendEquation BlendEquation, GrBlendCoeff SrcCoeff, GrBlendCoeff DstCoeff>
    struct get_properties : SkTIntegralConstant<Properties, static_cast<Properties>(

        (GR_BLEND_MODIFIES_DST(BlendEquation, SrcCoeff, DstCoeff) ?
            kModifiesDst_Property : 0) |

        (GR_BLEND_COEFFS_USE_DST_COLOR(SrcCoeff, DstCoeff) ?
            kUsesDstColor_Property : 0) |

        ((PrimaryOut >= kModulate_OutputType && GR_BLEND_COEFFS_USE_SRC_COLOR(SrcCoeff,DstCoeff)) ||
         (SecondaryOut >= kModulate_OutputType && GR_BLEND_COEFF_REFS_SRC2(DstCoeff)) ?
            kUsesInputColor_Property : 0) |  // We assert later that SrcCoeff doesn't ref src2.

        (kModulate_OutputType == PrimaryOut &&
         kNone_OutputType == SecondaryOut &&
         GR_BLEND_CAN_TWEAK_ALPHA_FOR_COVERAGE(BlendEquation, SrcCoeff, DstCoeff) ?
            kCanTweakAlphaForCoverage_Property : 0))> {

        // The provided formula should already be optimized.
        GR_STATIC_ASSERT((kNone_OutputType == PrimaryOut) ==
                         !GR_BLEND_COEFFS_USE_SRC_COLOR(SrcCoeff, DstCoeff));
        GR_STATIC_ASSERT(!GR_BLEND_COEFF_REFS_SRC2(SrcCoeff));
        GR_STATIC_ASSERT((kNone_OutputType == SecondaryOut) ==
                         !GR_BLEND_COEFF_REFS_SRC2(DstCoeff));
        GR_STATIC_ASSERT(PrimaryOut != SecondaryOut || kNone_OutputType == PrimaryOut);
        GR_STATIC_ASSERT(kNone_OutputType != PrimaryOut || kNone_OutputType == SecondaryOut);
    };

    union {
        struct {
            // We allot the enums one more bit than they require because MSVC seems to sign-extend
            // them when the top bit is set. (This is in violation of the C++03 standard 9.6/4)
            OutputType        fPrimaryOutputType    : 4;
            OutputType        fSecondaryOutputType  : 4;
            GrBlendEquation   fBlendEquation        : 6;
            GrBlendCoeff      fSrcCoeff             : 6;
            GrBlendCoeff      fDstCoeff             : 6;
            Properties        fProps                : 32 - (4 + 4 + 6 + 6 + 6);
        };
        uint32_t fData;
    };

    GR_STATIC_ASSERT(kLast_OutputType      < (1 << 3));
    GR_STATIC_ASSERT(kLast_GrBlendEquation < (1 << 5));
    GR_STATIC_ASSERT(kLast_GrBlendCoeff    < (1 << 5));
    GR_STATIC_ASSERT(kLast_Property        < (1 << 6));
};

GR_STATIC_ASSERT(4 == sizeof(BlendFormula));

GR_MAKE_BITFIELD_OPS(BlendFormula::Properties);

/**
 * Initialize a compile-time constant BlendFormula and automatically deduce fProps.
 */
#define INIT_BLEND_FORMULA(PRIMARY_OUT, SECONDARY_OUT, BLEND_EQUATION, SRC_COEFF, DST_COEFF) \
    {{{PRIMARY_OUT, \
       SECONDARY_OUT, \
       BLEND_EQUATION, SRC_COEFF, DST_COEFF, \
       BlendFormula::get_properties<PRIMARY_OUT, SECONDARY_OUT, \
                                    BLEND_EQUATION, SRC_COEFF, DST_COEFF>::value}}}

/**
 * When there is no coverage, or the blend mode can tweak alpha for coverage, we use the standard
 * Porter Duff formula.
 */
#define COEFF_FORMULA(SRC_COEFF, DST_COEFF) \
    INIT_BLEND_FORMULA(BlendFormula::kModulate_OutputType, \
                       BlendFormula::kNone_OutputType, \
                       kAdd_GrBlendEquation, SRC_COEFF, DST_COEFF)

/**
 * When the coeffs are (Zero, Zero), we clear the dst. This formula has its own macro so we can set
 * the primary output type to none.
 */
#define DST_CLEAR_FORMULA \
    INIT_BLEND_FORMULA(BlendFormula::kNone_OutputType, \
                       BlendFormula::kNone_OutputType, \
                       kAdd_GrBlendEquation, kZero_GrBlendCoeff, kZero_GrBlendCoeff)

/**
 * When the coeffs are (Zero, One), we don't write to the dst at all. This formula has its own macro
 * so we can set the primary output type to none.
 */
#define NO_DST_WRITE_FORMULA \
    INIT_BLEND_FORMULA(BlendFormula::kNone_OutputType, \
                       BlendFormula::kNone_OutputType, \
                       kAdd_GrBlendEquation, kZero_GrBlendCoeff, kOne_GrBlendCoeff)

/**
 * When there is coverage, the equation with f=coverage is:
 *
 *   D' = f * (S * srcCoeff + D * dstCoeff) + (1-f) * D
 *
 * This can be rewritten as:
 *
 *   D' = f * S * srcCoeff + D * (1 - [f * (1 - dstCoeff)])
 *
 * To implement this formula, we output [f * (1 - dstCoeff)] for the secondary color and replace the
 * HW dst coeff with IS2C.
 *
 * Xfer modes: dst-atop (Sa!=1)
 */
#define COVERAGE_FORMULA(ONE_MINUS_DST_COEFF_MODULATE_OUTPUT, SRC_COEFF) \
    INIT_BLEND_FORMULA(BlendFormula::kModulate_OutputType, \
                       ONE_MINUS_DST_COEFF_MODULATE_OUTPUT, \
                       kAdd_GrBlendEquation, SRC_COEFF, kIS2C_GrBlendCoeff)

/**
 * When there is coverage and the src coeff is Zero, the equation with f=coverage becomes:
 *
 *   D' = f * D * dstCoeff + (1-f) * D
 *
 * This can be rewritten as:
 *
 *   D' = D - D * [f * (1 - dstCoeff)]
 *
 * To implement this formula, we output [f * (1 - dstCoeff)] for the primary color and use a reverse
 * subtract HW blend equation with coeffs of (DC, One).
 *
 * Xfer modes: clear, dst-out (Sa=1), dst-in (Sa!=1), modulate (Sc!=1)
 */
#define COVERAGE_SRC_COEFF_ZERO_FORMULA(ONE_MINUS_DST_COEFF_MODULATE_OUTPUT) \
    INIT_BLEND_FORMULA(ONE_MINUS_DST_COEFF_MODULATE_OUTPUT, \
                       BlendFormula::kNone_OutputType, \
                       kReverseSubtract_GrBlendEquation, kDC_GrBlendCoeff, kOne_GrBlendCoeff)

/**
 * When there is coverage and the dst coeff is Zero, the equation with f=coverage becomes:
 *
 *   D' = f * S * srcCoeff + (1-f) * D
 *
 * To implement this formula, we output [f] for the secondary color and replace the HW dst coeff
 * with IS2A. (Note that we can avoid dual source blending when Sa=1 by using ISA.)
 *
 * Xfer modes (Sa!=1): src, src-in, src-out
 */
#define COVERAGE_DST_COEFF_ZERO_FORMULA(SRC_COEFF) \
    INIT_BLEND_FORMULA(BlendFormula::kModulate_OutputType, \
                       BlendFormula::kCoverage_OutputType, \
                       kAdd_GrBlendEquation, SRC_COEFF, kIS2A_GrBlendCoeff)

/**
 * This table outlines the blend formulas we will use with each xfermode, with and without coverage,
 * with and without an opaque input color. Optimization properties are deduced at compile time so we
 * can make runtime decisions quickly. RGB coverage is not supported.
 */
static const BlendFormula gBlendTable[2][2][SkXfermode::kLastCoeffMode + 1] = {

                     /*>> Has coverage, input color unknown <<*/ {{

    /* clear */      COVERAGE_SRC_COEFF_ZERO_FORMULA(BlendFormula::kCoverage_OutputType),
    /* src */        COVERAGE_DST_COEFF_ZERO_FORMULA(kOne_GrBlendCoeff),
    /* dst */        NO_DST_WRITE_FORMULA,
    /* src-over */   COEFF_FORMULA(   kOne_GrBlendCoeff,    kISA_GrBlendCoeff),
    /* dst-over */   COEFF_FORMULA(   kIDA_GrBlendCoeff,    kOne_GrBlendCoeff),
    /* src-in */     COVERAGE_DST_COEFF_ZERO_FORMULA(kDA_GrBlendCoeff),
    /* dst-in */     COVERAGE_SRC_COEFF_ZERO_FORMULA(BlendFormula::kISAModulate_OutputType),
    /* src-out */    COVERAGE_DST_COEFF_ZERO_FORMULA(kIDA_GrBlendCoeff),
    /* dst-out */    COEFF_FORMULA(   kZero_GrBlendCoeff,   kISA_GrBlendCoeff),
    /* src-atop */   COEFF_FORMULA(   kDA_GrBlendCoeff,     kISA_GrBlendCoeff),
    /* dst-atop */   COVERAGE_FORMULA(BlendFormula::kISAModulate_OutputType, kIDA_GrBlendCoeff),
    /* xor */        COEFF_FORMULA(   kIDA_GrBlendCoeff,    kISA_GrBlendCoeff),
    /* plus */       COEFF_FORMULA(   kOne_GrBlendCoeff,    kOne_GrBlendCoeff),
    /* modulate */   COVERAGE_SRC_COEFF_ZERO_FORMULA(BlendFormula::kISCModulate_OutputType),
    /* screen */     COEFF_FORMULA(   kOne_GrBlendCoeff,    kISC_GrBlendCoeff),

                     }, /*>> No coverage, input color unknown <<*/ {

    /* clear */      DST_CLEAR_FORMULA,
    /* src */        COEFF_FORMULA(   kOne_GrBlendCoeff,    kZero_GrBlendCoeff),
    /* dst */        NO_DST_WRITE_FORMULA,
    /* src-over */   COEFF_FORMULA(   kOne_GrBlendCoeff,    kISA_GrBlendCoeff),
    /* dst-over */   COEFF_FORMULA(   kIDA_GrBlendCoeff,    kOne_GrBlendCoeff),
    /* src-in */     COEFF_FORMULA(   kDA_GrBlendCoeff,     kZero_GrBlendCoeff),
    /* dst-in */     COEFF_FORMULA(   kZero_GrBlendCoeff,   kSA_GrBlendCoeff),
    /* src-out */    COEFF_FORMULA(   kIDA_GrBlendCoeff,    kZero_GrBlendCoeff),
    /* dst-out */    COEFF_FORMULA(   kZero_GrBlendCoeff,   kISA_GrBlendCoeff),
    /* src-atop */   COEFF_FORMULA(   kDA_GrBlendCoeff,     kISA_GrBlendCoeff),
    /* dst-atop */   COEFF_FORMULA(   kIDA_GrBlendCoeff,    kSA_GrBlendCoeff),
    /* xor */        COEFF_FORMULA(   kIDA_GrBlendCoeff,    kISA_GrBlendCoeff),
    /* plus */       COEFF_FORMULA(   kOne_GrBlendCoeff,    kOne_GrBlendCoeff),
    /* modulate */   COEFF_FORMULA(   kZero_GrBlendCoeff,   kSC_GrBlendCoeff),
    /* screen */     COEFF_FORMULA(   kOne_GrBlendCoeff,    kISC_GrBlendCoeff),

                     }}, /*>> Has coverage, input color opaque <<*/ {{

    /* clear */      COVERAGE_SRC_COEFF_ZERO_FORMULA(BlendFormula::kCoverage_OutputType),
    /* src */        COEFF_FORMULA(   kOne_GrBlendCoeff,    kISA_GrBlendCoeff),
    /* dst */        NO_DST_WRITE_FORMULA,
    /* src-over */   COEFF_FORMULA(   kOne_GrBlendCoeff,    kISA_GrBlendCoeff),
    /* dst-over */   COEFF_FORMULA(   kIDA_GrBlendCoeff,    kOne_GrBlendCoeff),
    /* src-in */     COEFF_FORMULA(   kDA_GrBlendCoeff,     kISA_GrBlendCoeff),
    /* dst-in */     NO_DST_WRITE_FORMULA,
    /* src-out */    COEFF_FORMULA(   kIDA_GrBlendCoeff,    kISA_GrBlendCoeff),
    /* dst-out */    COVERAGE_SRC_COEFF_ZERO_FORMULA(BlendFormula::kCoverage_OutputType),
    /* src-atop */   COEFF_FORMULA(   kDA_GrBlendCoeff,     kISA_GrBlendCoeff),
    /* dst-atop */   COEFF_FORMULA(   kIDA_GrBlendCoeff,    kOne_GrBlendCoeff),
    /* xor */        COEFF_FORMULA(   kIDA_GrBlendCoeff,    kISA_GrBlendCoeff),
    /* plus */       COEFF_FORMULA(   kOne_GrBlendCoeff,    kOne_GrBlendCoeff),
    /* modulate */   COVERAGE_SRC_COEFF_ZERO_FORMULA(BlendFormula::kISCModulate_OutputType),
    /* screen */     COEFF_FORMULA(   kOne_GrBlendCoeff,    kISC_GrBlendCoeff),

                     }, /*>> No coverage, input color opaque <<*/ {

    /* clear */      DST_CLEAR_FORMULA,
    /* src */        COEFF_FORMULA(   kOne_GrBlendCoeff,    kZero_GrBlendCoeff),
    /* dst */        NO_DST_WRITE_FORMULA,
    /* src-over */   COEFF_FORMULA(   kOne_GrBlendCoeff,    kZero_GrBlendCoeff),
    /* dst-over */   COEFF_FORMULA(   kIDA_GrBlendCoeff,    kOne_GrBlendCoeff),
    /* src-in */     COEFF_FORMULA(   kDA_GrBlendCoeff,     kZero_GrBlendCoeff),
    /* dst-in */     NO_DST_WRITE_FORMULA,
    /* src-out */    COEFF_FORMULA(   kIDA_GrBlendCoeff,    kZero_GrBlendCoeff),
    /* dst-out */    DST_CLEAR_FORMULA,
    /* src-atop */   COEFF_FORMULA(   kDA_GrBlendCoeff,     kZero_GrBlendCoeff),
    /* dst-atop */   COEFF_FORMULA(   kIDA_GrBlendCoeff,    kOne_GrBlendCoeff),
    /* xor */        COEFF_FORMULA(   kIDA_GrBlendCoeff,    kZero_GrBlendCoeff),
    /* plus */       COEFF_FORMULA(   kOne_GrBlendCoeff,    kOne_GrBlendCoeff),
    /* modulate */   COEFF_FORMULA(   kZero_GrBlendCoeff,   kSC_GrBlendCoeff),
    /* screen */     COEFF_FORMULA(   kOne_GrBlendCoeff,    kISC_GrBlendCoeff),
}}};

static BlendFormula get_blend_formula(SkXfermode::Mode xfermode,
                                      const GrProcOptInfo& colorPOI,
                                      const GrProcOptInfo& coveragePOI) {
    SkASSERT(xfermode >= 0 && xfermode <= SkXfermode::kLastCoeffMode);
    SkASSERT(!coveragePOI.isFourChannelOutput());

    return gBlendTable[colorPOI.isOpaque()][coveragePOI.isSolidWhite()][xfermode];
}

static BlendFormula get_unoptimized_blend_formula(SkXfermode::Mode xfermode) {
    SkASSERT(xfermode >= 0 && xfermode <= SkXfermode::kLastCoeffMode);

    return gBlendTable[0][0][xfermode];
}

///////////////////////////////////////////////////////////////////////////////

class PorterDuffXferProcessor : public GrXferProcessor {
public:
    static GrXferProcessor* Create(SkXfermode::Mode xfermode, const GrDeviceCoordTexture* dstCopy,
                                   bool willReadDstColor) {
        return SkNEW_ARGS(PorterDuffXferProcessor, (xfermode, dstCopy, willReadDstColor));
    }

    ~PorterDuffXferProcessor() override;

    const char* name() const override { return "Porter Duff"; }

    GrGLXferProcessor* createGLInstance() const override;

    bool hasSecondaryOutput() const override {
        return fBlendFormula.hasSecondaryOutput();
    }

    SkXfermode::Mode getXfermode() const { return fXfermode; }
    BlendFormula getBlendFormula() const { return fBlendFormula; }

private:
    PorterDuffXferProcessor(SkXfermode::Mode, const GrDeviceCoordTexture* dstCopy,
                            bool willReadDstColor);

    GrXferProcessor::OptFlags onGetOptimizations(const GrProcOptInfo& colorPOI,
                                                 const GrProcOptInfo& coveragePOI,
                                                 bool doesStencilWrite,
                                                 GrColor* overrideColor,
                                                 const GrCaps& caps) override;

    void onGetGLProcessorKey(const GrGLSLCaps& caps, GrProcessorKeyBuilder* b) const override;

    void onGetBlendInfo(GrXferProcessor::BlendInfo* blendInfo) const override {
        if (!this->willReadDstColor()) {
            blendInfo->fEquation = fBlendFormula.fBlendEquation;
            blendInfo->fSrcBlend = fBlendFormula.fSrcCoeff;
            blendInfo->fDstBlend = fBlendFormula.fDstCoeff;
            blendInfo->fWriteColor = fBlendFormula.modifiesDst();
        }
    }

    bool onIsEqual(const GrXferProcessor& xpBase) const override {
        const PorterDuffXferProcessor& xp = xpBase.cast<PorterDuffXferProcessor>();
        return fXfermode == xp.fXfermode &&
               fBlendFormula == xp.fBlendFormula;
    }

    SkXfermode::Mode fXfermode;
    BlendFormula     fBlendFormula;

    typedef GrXferProcessor INHERITED;
};

///////////////////////////////////////////////////////////////////////////////

void append_color_output(const PorterDuffXferProcessor& xp, GrGLXPFragmentBuilder* fsBuilder,
                         BlendFormula::OutputType outputType, const char* output,
                         const char* inColor, const char* inCoverage) {
    switch (outputType) {
        case BlendFormula::kNone_OutputType:
            fsBuilder->codeAppendf("%s = vec4(0.0);", output);
            break;
        case BlendFormula::kCoverage_OutputType:
            fsBuilder->codeAppendf("%s = %s;",
                                   output, xp.readsCoverage() ? inCoverage : "vec4(1.0)");
            break;
        case BlendFormula::kModulate_OutputType:
            if (xp.readsCoverage()) {
                fsBuilder->codeAppendf("%s = %s * %s;", output, inColor, inCoverage);
            } else {
                fsBuilder->codeAppendf("%s = %s;", output, inColor);
            }
            break;
        case BlendFormula::kISAModulate_OutputType:
            if (xp.readsCoverage()) {
                fsBuilder->codeAppendf("%s = (1.0 - %s.a) * %s;", output, inColor, inCoverage);
            } else {
                fsBuilder->codeAppendf("%s = vec4(1.0 - %s.a);", output, inColor);
            }
            break;
        case BlendFormula::kISCModulate_OutputType:
            if (xp.readsCoverage()) {
                fsBuilder->codeAppendf("%s = (vec4(1.0) - %s) * %s;", output, inColor, inCoverage);
            } else {
                fsBuilder->codeAppendf("%s = vec4(1.0) - %s;", output, inColor);
            }
            break;
        default:
            SkFAIL("Unsupported output type.");
            break;
    }
}

bool append_porterduff_term(GrGLXPFragmentBuilder* fsBuilder, SkXfermode::Coeff coeff,
                            const char* colorName, const char* srcColorName,
                            const char* dstColorName, bool hasPrevious) {
    if (SkXfermode::kZero_Coeff == coeff) {
        return hasPrevious;
    } else {
        if (hasPrevious) {
            fsBuilder->codeAppend(" + ");
        }
        fsBuilder->codeAppendf("%s", colorName);
        switch (coeff) {
            case SkXfermode::kOne_Coeff:
                break;
            case SkXfermode::kSC_Coeff:
                fsBuilder->codeAppendf(" * %s", srcColorName); 
                break;
            case SkXfermode::kISC_Coeff:
                fsBuilder->codeAppendf(" * (vec4(1.0) - %s)", srcColorName); 
                break;
            case SkXfermode::kDC_Coeff:
                fsBuilder->codeAppendf(" * %s", dstColorName); 
                break;
            case SkXfermode::kIDC_Coeff:
                fsBuilder->codeAppendf(" * (vec4(1.0) - %s)", dstColorName); 
                break;
            case SkXfermode::kSA_Coeff:
                fsBuilder->codeAppendf(" * %s.a", srcColorName); 
                break;
            case SkXfermode::kISA_Coeff:
                fsBuilder->codeAppendf(" * (1.0 - %s.a)", srcColorName); 
                break;
            case SkXfermode::kDA_Coeff:
                fsBuilder->codeAppendf(" * %s.a", dstColorName); 
                break;
            case SkXfermode::kIDA_Coeff:
                fsBuilder->codeAppendf(" * (1.0 - %s.a)", dstColorName); 
                break;
            default:
                SkFAIL("Unsupported Blend Coeff");
        }
        return true;
    }
}

class GLPorterDuffXferProcessor : public GrGLXferProcessor {
public:
    GLPorterDuffXferProcessor(const GrProcessor&) {}

    virtual ~GLPorterDuffXferProcessor() {}

    static void GenKey(const GrProcessor& processor, const GrGLSLCaps& caps,
                       GrProcessorKeyBuilder* b) {
        const PorterDuffXferProcessor& xp = processor.cast<PorterDuffXferProcessor>();
        if (xp.willReadDstColor()) {
            b->add32(xp.getXfermode());  // Parent class includes willReadDstColor() in key.
        } else {
            b->add32(SkToInt(xp.readsCoverage()) |
                     (xp.getBlendFormula().fPrimaryOutputType << 1) |
                     (xp.getBlendFormula().fSecondaryOutputType << 4));
            GR_STATIC_ASSERT(BlendFormula::kLast_OutputType < 8);
        }
    };

private:
    void onEmitCode(const EmitArgs& args) override {
        const PorterDuffXferProcessor& xp = args.fXP.cast<PorterDuffXferProcessor>();
        GrGLXPFragmentBuilder* fsBuilder = args.fPB->getFragmentShaderBuilder();
        if (!xp.willReadDstColor()) {
            BlendFormula blendFormula = xp.getBlendFormula();
            if (blendFormula.hasSecondaryOutput()) {
                append_color_output(xp, fsBuilder, blendFormula.fSecondaryOutputType,
                                    args.fOutputSecondary, args.fInputColor, args.fInputCoverage);
            }
            append_color_output(xp, fsBuilder, blendFormula.fPrimaryOutputType,
                                args.fOutputPrimary, args.fInputColor, args.fInputCoverage);
        } else {
            SkASSERT(xp.willReadDstColor());

            SkXfermode::Coeff srcCoeff, dstCoeff;
            SkXfermode::ModeAsCoeff(xp.getXfermode(), &srcCoeff, &dstCoeff);

            const char* dstColor = fsBuilder->dstColor();

            fsBuilder->codeAppend("vec4 colorBlend =");
            // append src blend
            bool didAppend = append_porterduff_term(fsBuilder, srcCoeff,
                                                    args.fInputColor, args.fInputColor,
                                                    dstColor, false);
            // append dst blend
            SkAssertResult(append_porterduff_term(fsBuilder, dstCoeff,
                                                  dstColor, args.fInputColor,
                                                  dstColor, didAppend));
            fsBuilder->codeAppend(";");

            fsBuilder->codeAppendf("%s = %s * colorBlend + (vec4(1.0) - %s) * %s;",
                                   args.fOutputPrimary, args.fInputCoverage, args.fInputCoverage,
                                   dstColor);
        }
    }

    void onSetData(const GrGLProgramDataManager&, const GrXferProcessor&) override {};

    typedef GrGLXferProcessor INHERITED;
};

///////////////////////////////////////////////////////////////////////////////

PorterDuffXferProcessor::PorterDuffXferProcessor(SkXfermode::Mode xfermode,
                                                 const GrDeviceCoordTexture* dstCopy,
                                                 bool willReadDstColor)
    : INHERITED(dstCopy, willReadDstColor)
    , fXfermode(xfermode)
    , fBlendFormula(get_unoptimized_blend_formula(xfermode)) {
    this->initClassID<PorterDuffXferProcessor>();
}

PorterDuffXferProcessor::~PorterDuffXferProcessor() {
}

void PorterDuffXferProcessor::onGetGLProcessorKey(const GrGLSLCaps& caps,
                                                  GrProcessorKeyBuilder* b) const {
    GLPorterDuffXferProcessor::GenKey(*this, caps, b);
}

GrGLXferProcessor* PorterDuffXferProcessor::createGLInstance() const {
    return SkNEW_ARGS(GLPorterDuffXferProcessor, (*this));
}

GrXferProcessor::OptFlags
PorterDuffXferProcessor::onGetOptimizations(const GrProcOptInfo& colorPOI,
                                            const GrProcOptInfo& coveragePOI,
                                            bool doesStencilWrite,
                                            GrColor* overrideColor,
                                            const GrCaps& caps) {
    if (this->willReadDstColor()) {
        return GrXferProcessor::kNone_Opt;
    }

    fBlendFormula = get_blend_formula(fXfermode, colorPOI, coveragePOI);

    GrXferProcessor::OptFlags optFlags = GrXferProcessor::kNone_Opt;
    if (!fBlendFormula.modifiesDst()) {
        if (!doesStencilWrite) {
            optFlags |= GrXferProcessor::kSkipDraw_OptFlag;
        }
        optFlags |= (GrXferProcessor::kIgnoreColor_OptFlag |
                     GrXferProcessor::kIgnoreCoverage_OptFlag |
                     GrXferProcessor::kCanTweakAlphaForCoverage_OptFlag);
    } else {
        if (!fBlendFormula.usesInputColor()) {
            optFlags |= GrXferProcessor::kIgnoreColor_OptFlag;
        }
        if (coveragePOI.isSolidWhite()) {
            optFlags |= GrXferProcessor::kIgnoreCoverage_OptFlag;
        }
        if (colorPOI.allStagesMultiplyInput() && fBlendFormula.canTweakAlphaForCoverage()) {
            optFlags |= GrXferProcessor::kCanTweakAlphaForCoverage_OptFlag;
        }
    }

    return optFlags;
}

///////////////////////////////////////////////////////////////////////////////

class PDLCDXferProcessor : public GrXferProcessor {
public:
    static GrXferProcessor* Create(SkXfermode::Mode xfermode, const GrProcOptInfo& colorPOI);

    ~PDLCDXferProcessor() override;

    const char* name() const override { return "Porter Duff LCD"; }

    GrGLXferProcessor* createGLInstance() const override;

    bool hasSecondaryOutput() const override { return false; }

private:
    PDLCDXferProcessor(GrColor blendConstant, uint8_t alpha);

    GrXferProcessor::OptFlags onGetOptimizations(const GrProcOptInfo& colorPOI,
                                                 const GrProcOptInfo& coveragePOI,
                                                 bool doesStencilWrite,
                                                 GrColor* overrideColor,
                                                 const GrCaps& caps) override;

    void onGetGLProcessorKey(const GrGLSLCaps& caps, GrProcessorKeyBuilder* b) const override;

    void onGetBlendInfo(GrXferProcessor::BlendInfo* blendInfo) const override {
        blendInfo->fSrcBlend = kConstC_GrBlendCoeff;
        blendInfo->fDstBlend = kISC_GrBlendCoeff;
        blendInfo->fBlendConstant = fBlendConstant;
    }

    bool onIsEqual(const GrXferProcessor& xpBase) const override {
        const PDLCDXferProcessor& xp = xpBase.cast<PDLCDXferProcessor>();
        if (fBlendConstant != xp.fBlendConstant ||
            fAlpha != xp.fAlpha) {
            return false;
        }
        return true;
    }

    GrColor      fBlendConstant;
    uint8_t      fAlpha;

    typedef GrXferProcessor INHERITED;
};

///////////////////////////////////////////////////////////////////////////////

class GLPDLCDXferProcessor : public GrGLXferProcessor {
public:
    GLPDLCDXferProcessor(const GrProcessor&) {}

    virtual ~GLPDLCDXferProcessor() {}

    static void GenKey(const GrProcessor& processor, const GrGLSLCaps& caps,
                       GrProcessorKeyBuilder* b) {}

private:
    void onEmitCode(const EmitArgs& args) override {
        GrGLXPFragmentBuilder* fsBuilder = args.fPB->getFragmentShaderBuilder();

        fsBuilder->codeAppendf("%s = %s * %s;", args.fOutputPrimary, args.fInputColor,
                               args.fInputCoverage);
    }

    void onSetData(const GrGLProgramDataManager&, const GrXferProcessor&) override {};

    typedef GrGLXferProcessor INHERITED;
};

///////////////////////////////////////////////////////////////////////////////

PDLCDXferProcessor::PDLCDXferProcessor(GrColor blendConstant, uint8_t alpha)
    : fBlendConstant(blendConstant)
    , fAlpha(alpha) {
    this->initClassID<PDLCDXferProcessor>();
}

GrXferProcessor* PDLCDXferProcessor::Create(SkXfermode::Mode xfermode,
                                            const GrProcOptInfo& colorPOI) {
    if (SkXfermode::kSrcOver_Mode != xfermode) {
        return NULL;
    }

    if (kRGBA_GrColorComponentFlags != colorPOI.validFlags()) {
        return NULL;
    }

    GrColor blendConstant = GrUnPreMulColor(colorPOI.color());
    uint8_t alpha = GrColorUnpackA(blendConstant);
    blendConstant |= (0xff << GrColor_SHIFT_A);

    return SkNEW_ARGS(PDLCDXferProcessor, (blendConstant, alpha));
}

PDLCDXferProcessor::~PDLCDXferProcessor() {
}

void PDLCDXferProcessor::onGetGLProcessorKey(const GrGLSLCaps& caps,
                                             GrProcessorKeyBuilder* b) const {
    GLPDLCDXferProcessor::GenKey(*this, caps, b);
}

GrGLXferProcessor* PDLCDXferProcessor::createGLInstance() const {
    return SkNEW_ARGS(GLPDLCDXferProcessor, (*this));
}

GrXferProcessor::OptFlags
PDLCDXferProcessor::onGetOptimizations(const GrProcOptInfo& colorPOI,
                                       const GrProcOptInfo& coveragePOI,
                                       bool doesStencilWrite,
                                       GrColor* overrideColor,
                                       const GrCaps& caps) {
        // We want to force our primary output to be alpha * Coverage, where alpha is the alpha
        // value of the blend the constant. We should already have valid blend coeff's if we are at
        // a point where we have RGB coverage. We don't need any color stages since the known color
        // output is already baked into the blendConstant.
        *overrideColor = GrColorPackRGBA(fAlpha, fAlpha, fAlpha, fAlpha);
        return GrXferProcessor::kOverrideColor_OptFlag;
}

///////////////////////////////////////////////////////////////////////////////

GrPorterDuffXPFactory::GrPorterDuffXPFactory(SkXfermode::Mode xfermode)
    : fXfermode(xfermode) {
    this->initClassID<GrPorterDuffXPFactory>();
}

GrXPFactory* GrPorterDuffXPFactory::Create(SkXfermode::Mode xfermode) {
    static GrPorterDuffXPFactory gClearPDXPF(SkXfermode::kClear_Mode);
    static GrPorterDuffXPFactory gSrcPDXPF(SkXfermode::kSrc_Mode);
    static GrPorterDuffXPFactory gDstPDXPF(SkXfermode::kDst_Mode);
    static GrPorterDuffXPFactory gSrcOverPDXPF(SkXfermode::kSrcOver_Mode);
    static GrPorterDuffXPFactory gDstOverPDXPF(SkXfermode::kDstOver_Mode);
    static GrPorterDuffXPFactory gSrcInPDXPF(SkXfermode::kSrcIn_Mode);
    static GrPorterDuffXPFactory gDstInPDXPF(SkXfermode::kDstIn_Mode);
    static GrPorterDuffXPFactory gSrcOutPDXPF(SkXfermode::kSrcOut_Mode);
    static GrPorterDuffXPFactory gDstOutPDXPF(SkXfermode::kDstOut_Mode);
    static GrPorterDuffXPFactory gSrcATopPDXPF(SkXfermode::kSrcATop_Mode);
    static GrPorterDuffXPFactory gDstATopPDXPF(SkXfermode::kDstATop_Mode);
    static GrPorterDuffXPFactory gXorPDXPF(SkXfermode::kXor_Mode);
    static GrPorterDuffXPFactory gPlusPDXPF(SkXfermode::kPlus_Mode);
    static GrPorterDuffXPFactory gModulatePDXPF(SkXfermode::kModulate_Mode);
    static GrPorterDuffXPFactory gScreenPDXPF(SkXfermode::kScreen_Mode);

    static GrPorterDuffXPFactory* gFactories[] = {
        &gClearPDXPF, &gSrcPDXPF, &gDstPDXPF, &gSrcOverPDXPF, &gDstOverPDXPF, &gSrcInPDXPF,
        &gDstInPDXPF, &gSrcOutPDXPF, &gDstOutPDXPF, &gSrcATopPDXPF, &gDstATopPDXPF, &gXorPDXPF,
        &gPlusPDXPF, &gModulatePDXPF, &gScreenPDXPF
    };
    GR_STATIC_ASSERT(SK_ARRAY_COUNT(gFactories) == SkXfermode::kLastCoeffMode + 1);

    if (xfermode < 0 || xfermode > SkXfermode::kLastCoeffMode) {
        return NULL;
    }
    return SkRef(gFactories[xfermode]);
}

GrXferProcessor*
GrPorterDuffXPFactory::onCreateXferProcessor(const GrCaps& caps,
                                             const GrProcOptInfo& colorPOI,
                                             const GrProcOptInfo& covPOI,
                                             const GrDeviceCoordTexture* dstCopy) const {
    if (covPOI.isFourChannelOutput()) {
        return PDLCDXferProcessor::Create(fXfermode, colorPOI);
    } else {
        return PorterDuffXferProcessor::Create(fXfermode, dstCopy,
                                               this->willReadDstColor(caps, colorPOI, covPOI));
    }
}

bool GrPorterDuffXPFactory::supportsRGBCoverage(GrColor /*knownColor*/,
                                                uint32_t knownColorFlags) const {
    if (SkXfermode::kSrcOver_Mode == fXfermode &&
        kRGBA_GrColorComponentFlags == knownColorFlags) {
        return true;
    }
    return false;
}

void GrPorterDuffXPFactory::getInvariantOutput(const GrProcOptInfo& colorPOI,
                                               const GrProcOptInfo& coveragePOI,
                                               GrXPFactory::InvariantOutput* output) const {
    const BlendFormula& blendFormula = get_blend_formula(fXfermode, colorPOI, coveragePOI);

    if (blendFormula.usesDstColor()) {
        output->fWillBlendWithDst = true;
        output->fBlendedColorFlags = kNone_GrColorComponentFlags;
        return;
    }

    SkASSERT(coveragePOI.isSolidWhite());
    SkASSERT(kAdd_GrBlendEquation == blendFormula.fBlendEquation);

    output->fWillBlendWithDst = false;

    switch (blendFormula.fSrcCoeff) {
        case kZero_GrBlendCoeff:
            output->fBlendedColor = 0;
            output->fBlendedColorFlags = kRGBA_GrColorComponentFlags;
            return;

        case kOne_GrBlendCoeff:
            output->fBlendedColor = colorPOI.color();
            output->fBlendedColorFlags = colorPOI.validFlags();
            return;

        // TODO: update if we ever use const color.
        default:
            output->fBlendedColorFlags = kNone_GrColorComponentFlags;
            return;
    }
}

bool GrPorterDuffXPFactory::willReadDstColor(const GrCaps& caps,
                                             const GrProcOptInfo& colorPOI,
                                             const GrProcOptInfo& coveragePOI) const {
    // Some formulas use dual source blending, so we fall back if it is required but not supported.
    return !caps.shaderCaps()->dualSourceBlendingSupport() &&
           get_blend_formula(fXfermode, colorPOI, coveragePOI).hasSecondaryOutput();
}

GR_DEFINE_XP_FACTORY_TEST(GrPorterDuffXPFactory);

GrXPFactory* GrPorterDuffXPFactory::TestCreate(SkRandom* random,
                                               GrContext*,
                                               const GrCaps&,
                                               GrTexture*[]) {
    SkXfermode::Mode mode = SkXfermode::Mode(random->nextULessThan(SkXfermode::kLastCoeffMode));
    return GrPorterDuffXPFactory::Create(mode);
}

void GrPorterDuffXPFactory::TestGetXPOutputTypes(const GrXferProcessor* xp,
                                                 int* outPrimary,
                                                 int* outSecondary) {
    if (!!strcmp(xp->name(), "Porter Duff")) {
        *outPrimary = *outSecondary = -1;
        return;
    }
    BlendFormula blendFormula = static_cast<const PorterDuffXferProcessor*>(xp)->getBlendFormula();
    *outPrimary = blendFormula.fPrimaryOutputType;
    *outSecondary = blendFormula.fSecondaryOutputType;
}