GrBlend.h

/*
 * Copyright 2013 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#ifndef GrBlend_DEFINED
#define GrBlend_DEFINED

#include "GrColor.h"
#include "../private/SkTLogic.h"

enum GrBlendEquation {
    // Basic blend equations.
    kAdd_GrBlendEquation,             //<! Cs*S + Cd*D
    kSubtract_GrBlendEquation,        //<! Cs*S - Cd*D
    kReverseSubtract_GrBlendEquation, //<! Cd*D - Cs*S

    // Advanced blend equations. These are described in the SVG and PDF specs.
    kScreen_GrBlendEquation,
    kOverlay_GrBlendEquation,
    kDarken_GrBlendEquation,
    kLighten_GrBlendEquation,
    kColorDodge_GrBlendEquation,
    kColorBurn_GrBlendEquation,
    kHardLight_GrBlendEquation,
    kSoftLight_GrBlendEquation,
    kDifference_GrBlendEquation,
    kExclusion_GrBlendEquation,
    kMultiply_GrBlendEquation,
    kHSLHue_GrBlendEquation,
    kHSLSaturation_GrBlendEquation,
    kHSLColor_GrBlendEquation,
    kHSLLuminosity_GrBlendEquation,

    kFirstAdvancedGrBlendEquation = kScreen_GrBlendEquation,
    kLast_GrBlendEquation = kHSLLuminosity_GrBlendEquation
};

static const int kGrBlendEquationCnt = kLast_GrBlendEquation + 1;


enum GrBlendCoeff {
    kZero_GrBlendCoeff,    //<! 0
    kOne_GrBlendCoeff,     //<! 1
    kSC_GrBlendCoeff,      //<! src color
    kISC_GrBlendCoeff,     //<! one minus src color
    kDC_GrBlendCoeff,      //<! dst color
    kIDC_GrBlendCoeff,     //<! one minus dst color
    kSA_GrBlendCoeff,      //<! src alpha
    kISA_GrBlendCoeff,     //<! one minus src alpha
    kDA_GrBlendCoeff,      //<! dst alpha
    kIDA_GrBlendCoeff,     //<! one minus dst alpha
    kConstC_GrBlendCoeff,  //<! constant color
    kIConstC_GrBlendCoeff, //<! one minus constant color
    kConstA_GrBlendCoeff,  //<! constant color alpha
    kIConstA_GrBlendCoeff, //<! one minus constant color alpha
    kS2C_GrBlendCoeff,
    kIS2C_GrBlendCoeff,
    kS2A_GrBlendCoeff,
    kIS2A_GrBlendCoeff,

    kLast_GrBlendCoeff = kIS2A_GrBlendCoeff
};

static const int kGrBlendCoeffCnt = kLast_GrBlendCoeff + 1;

static constexpr bool GrBlendCoeffRefsSrc(const GrBlendCoeff coeff) {
    return kSC_GrBlendCoeff == coeff || kISC_GrBlendCoeff == coeff || kSA_GrBlendCoeff == coeff ||
           kISA_GrBlendCoeff == coeff;
}

static constexpr bool GrBlendCoeffRefsDst(const GrBlendCoeff coeff) {
    return kDC_GrBlendCoeff == coeff || kIDC_GrBlendCoeff == coeff || kDA_GrBlendCoeff == coeff ||
           kIDA_GrBlendCoeff == coeff;
}

static constexpr bool GrBlendCoeffRefsSrc2(const GrBlendCoeff coeff) {
    return kS2C_GrBlendCoeff == coeff || kIS2C_GrBlendCoeff == coeff ||
           kS2A_GrBlendCoeff == coeff || kIS2A_GrBlendCoeff == coeff;
}

static constexpr bool GrBlendCoeffsUseSrcColor(GrBlendCoeff srcCoeff, GrBlendCoeff dstCoeff) {
    return kZero_GrBlendCoeff != srcCoeff || GrBlendCoeffRefsSrc(dstCoeff);
}

static constexpr bool GrBlendCoeffsUseDstColor(GrBlendCoeff srcCoeff, GrBlendCoeff dstCoeff) {
    return GrBlendCoeffRefsDst(srcCoeff) || kZero_GrBlendCoeff != dstCoeff;
}

static constexpr bool GrBlendEquationIsAdvanced(GrBlendEquation equation) {
    return equation >= kFirstAdvancedGrBlendEquation;
}

static constexpr bool GrBlendModifiesDst(GrBlendEquation equation, GrBlendCoeff srcCoeff,
                                         GrBlendCoeff dstCoeff) {
    return (kAdd_GrBlendEquation != equation && kReverseSubtract_GrBlendEquation != equation) ||
           kZero_GrBlendCoeff != srcCoeff || kOne_GrBlendCoeff != dstCoeff;
}

static constexpr bool GrBlendAllowsCoverageAsAlpha(GrBlendEquation equation,
                                                   GrBlendCoeff srcCoeff,
                                                   GrBlendCoeff dstCoeff) {
    return GrBlendEquationIsAdvanced(equation) ||
           !GrBlendModifiesDst(equation, srcCoeff, dstCoeff) ||
           ((kAdd_GrBlendEquation == equation || kReverseSubtract_GrBlendEquation == equation) &&
            !GrBlendCoeffRefsSrc(srcCoeff) &&
            (kOne_GrBlendCoeff == dstCoeff || kISC_GrBlendCoeff == dstCoeff ||
             kISA_GrBlendCoeff == dstCoeff));
}

#endif