/* | |

* 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" | |

/** | |

* Equations for alpha-blending. | |

*/ | |

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; | |

/** | |

* Coefficients for alpha-blending. | |

*/ | |

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; | |

} | |

/** | |

* Advanced blend equations can always tweak alpha for coverage. (See GrCustomXfermode.cpp) | |

* | |

* For "add" and "reverse subtract" the blend equation with f=coverage is: | |

* | |

* D' = f * (S * srcCoeff + D * dstCoeff) + (1-f) * D | |

* = f * S * srcCoeff + D * (f * dstCoeff + (1 - f)) | |

* | |

* (Let srcCoeff be negative for reverse subtract.) We can tweak alpha for coverage when the | |

* following relationship holds: | |

* | |

* (f*S) * srcCoeff' + D * dstCoeff' == f * S * srcCoeff + D * (f * dstCoeff + (1 - f)) | |

* | |

* (Where srcCoeff' and dstCoeff' have any reference to S pre-multiplied by f.) | |

* | |

* It's easy to see this works for the src term as long as srcCoeff' == srcCoeff (meaning srcCoeff | |

* does not reference S). For the dst term, this will work as long as the following is true: | |

*| | |

* dstCoeff' == f * dstCoeff + (1 - f) | |

* dstCoeff' == 1 - f * (1 - dstCoeff) | |

* | |

* By inspection we can see this will work as long as dstCoeff has a 1, and any other term in | |

* dstCoeff references S. | |

* | |

* Moreover, if the blend doesn't modify the dst at all then it is ok to arbitrarily modify the src | |

* color so folding in coverage is allowed. | |

*/ | |

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 |