123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151 |
- /*
- * 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 "include/core/SkTypes.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,
- kIllegal_GrBlendEquation,
- kFirstAdvancedGrBlendEquation = kScreen_GrBlendEquation,
- kLast_GrBlendEquation = kIllegal_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,
- kIllegal_GrBlendCoeff,
- kLast_GrBlendCoeff = kIllegal_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
- && equation != kIllegal_GrBlendEquation;
- }
- 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
|