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152 lines
5.4 KiB
152 lines
5.4 KiB
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/*
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* Copyright 2013 Google Inc.
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*
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* Use of this source code is governed by a BSD-style license that can be
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* found in the LICENSE file.
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*/
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#ifndef GrBlend_DEFINED
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#define GrBlend_DEFINED
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#include "SkTypes.h"
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/**
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* Equations for alpha-blending.
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*/
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enum GrBlendEquation {
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// Basic blend equations.
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kAdd_GrBlendEquation, //<! Cs*S + Cd*D
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kSubtract_GrBlendEquation, //<! Cs*S - Cd*D
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kReverseSubtract_GrBlendEquation, //<! Cd*D - Cs*S
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// Advanced blend equations. These are described in the SVG and PDF specs.
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kScreen_GrBlendEquation,
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kOverlay_GrBlendEquation,
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kDarken_GrBlendEquation,
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kLighten_GrBlendEquation,
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kColorDodge_GrBlendEquation,
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kColorBurn_GrBlendEquation,
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kHardLight_GrBlendEquation,
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kSoftLight_GrBlendEquation,
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kDifference_GrBlendEquation,
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kExclusion_GrBlendEquation,
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kMultiply_GrBlendEquation,
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kHSLHue_GrBlendEquation,
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kHSLSaturation_GrBlendEquation,
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kHSLColor_GrBlendEquation,
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kHSLLuminosity_GrBlendEquation,
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kIllegal_GrBlendEquation,
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kFirstAdvancedGrBlendEquation = kScreen_GrBlendEquation,
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kLast_GrBlendEquation = kIllegal_GrBlendEquation,
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};
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static const int kGrBlendEquationCnt = kLast_GrBlendEquation + 1;
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/**
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* Coefficients for alpha-blending.
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*/
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enum GrBlendCoeff {
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kZero_GrBlendCoeff, //<! 0
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kOne_GrBlendCoeff, //<! 1
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kSC_GrBlendCoeff, //<! src color
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kISC_GrBlendCoeff, //<! one minus src color
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kDC_GrBlendCoeff, //<! dst color
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kIDC_GrBlendCoeff, //<! one minus dst color
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kSA_GrBlendCoeff, //<! src alpha
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kISA_GrBlendCoeff, //<! one minus src alpha
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kDA_GrBlendCoeff, //<! dst alpha
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kIDA_GrBlendCoeff, //<! one minus dst alpha
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kConstC_GrBlendCoeff, //<! constant color
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kIConstC_GrBlendCoeff, //<! one minus constant color
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kConstA_GrBlendCoeff, //<! constant color alpha
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kIConstA_GrBlendCoeff, //<! one minus constant color alpha
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kS2C_GrBlendCoeff,
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kIS2C_GrBlendCoeff,
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kS2A_GrBlendCoeff,
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kIS2A_GrBlendCoeff,
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kIllegal_GrBlendCoeff,
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kLast_GrBlendCoeff = kIllegal_GrBlendCoeff,
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};
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static const int kGrBlendCoeffCnt = kLast_GrBlendCoeff + 1;
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static constexpr bool GrBlendCoeffRefsSrc(const GrBlendCoeff coeff) {
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return kSC_GrBlendCoeff == coeff || kISC_GrBlendCoeff == coeff || kSA_GrBlendCoeff == coeff ||
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kISA_GrBlendCoeff == coeff;
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}
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static constexpr bool GrBlendCoeffRefsDst(const GrBlendCoeff coeff) {
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return kDC_GrBlendCoeff == coeff || kIDC_GrBlendCoeff == coeff || kDA_GrBlendCoeff == coeff ||
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kIDA_GrBlendCoeff == coeff;
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}
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static constexpr bool GrBlendCoeffRefsSrc2(const GrBlendCoeff coeff) {
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return kS2C_GrBlendCoeff == coeff || kIS2C_GrBlendCoeff == coeff ||
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kS2A_GrBlendCoeff == coeff || kIS2A_GrBlendCoeff == coeff;
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}
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static constexpr bool GrBlendCoeffsUseSrcColor(GrBlendCoeff srcCoeff, GrBlendCoeff dstCoeff) {
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return kZero_GrBlendCoeff != srcCoeff || GrBlendCoeffRefsSrc(dstCoeff);
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}
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static constexpr bool GrBlendCoeffsUseDstColor(GrBlendCoeff srcCoeff, GrBlendCoeff dstCoeff) {
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return GrBlendCoeffRefsDst(srcCoeff) || kZero_GrBlendCoeff != dstCoeff;
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}
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static constexpr bool GrBlendEquationIsAdvanced(GrBlendEquation equation) {
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return equation >= kFirstAdvancedGrBlendEquation
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&& equation != kIllegal_GrBlendEquation;
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}
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static constexpr bool GrBlendModifiesDst(GrBlendEquation equation, GrBlendCoeff srcCoeff,
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GrBlendCoeff dstCoeff) {
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return (kAdd_GrBlendEquation != equation && kReverseSubtract_GrBlendEquation != equation) ||
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kZero_GrBlendCoeff != srcCoeff || kOne_GrBlendCoeff != dstCoeff;
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}
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/**
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* Advanced blend equations can always tweak alpha for coverage. (See GrCustomXfermode.cpp)
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*
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* For "add" and "reverse subtract" the blend equation with f=coverage is:
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*
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* D' = f * (S * srcCoeff + D * dstCoeff) + (1-f) * D
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* = f * S * srcCoeff + D * (f * dstCoeff + (1 - f))
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*
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* (Let srcCoeff be negative for reverse subtract.) We can tweak alpha for coverage when the
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* following relationship holds:
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*
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* (f*S) * srcCoeff' + D * dstCoeff' == f * S * srcCoeff + D * (f * dstCoeff + (1 - f))
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*
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* (Where srcCoeff' and dstCoeff' have any reference to S pre-multiplied by f.)
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*
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* It's easy to see this works for the src term as long as srcCoeff' == srcCoeff (meaning srcCoeff
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* does not reference S). For the dst term, this will work as long as the following is true:
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*|
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* dstCoeff' == f * dstCoeff + (1 - f)
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* dstCoeff' == 1 - f * (1 - dstCoeff)
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*
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* By inspection we can see this will work as long as dstCoeff has a 1, and any other term in
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* dstCoeff references S.
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*
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* Moreover, if the blend doesn't modify the dst at all then it is ok to arbitrarily modify the src
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* color so folding in coverage is allowed.
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*/
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static constexpr bool GrBlendAllowsCoverageAsAlpha(GrBlendEquation equation,
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GrBlendCoeff srcCoeff,
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GrBlendCoeff dstCoeff) {
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return GrBlendEquationIsAdvanced(equation) ||
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!GrBlendModifiesDst(equation, srcCoeff, dstCoeff) ||
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((kAdd_GrBlendEquation == equation || kReverseSubtract_GrBlendEquation == equation) &&
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!GrBlendCoeffRefsSrc(srcCoeff) &&
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(kOne_GrBlendCoeff == dstCoeff || kISC_GrBlendCoeff == dstCoeff ||
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kISA_GrBlendCoeff == dstCoeff));
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}
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#endif
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