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/*
* 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;
/**
* Given a known blend equation in the form of srcCoeff * srcColor + dstCoeff * dstColor where
* there may be partial knowledge of the srcColor and dstColor component values, determine what
* components of the blended output color are known. Coeffs must not refer to the constant or
* secondary src color.
*/
void GrGetCoeffBlendKnownComponents(GrBlendCoeff srcCoeff, GrBlendCoeff dstCoeff,
GrColor srcColor,
GrColorComponentFlags srcColorFlags,
GrColor dstColor,
GrColorComponentFlags dstColorFlags,
GrColor* outColor,
GrColorComponentFlags* outFlags);
template<GrBlendCoeff Coeff>
struct GrTBlendCoeffRefsSrc : skstd::bool_constant<kSC_GrBlendCoeff == Coeff ||
kISC_GrBlendCoeff == Coeff ||
kSA_GrBlendCoeff == Coeff ||
kISA_GrBlendCoeff == Coeff> {};
#define GR_BLEND_COEFF_REFS_SRC(COEFF) \
GrTBlendCoeffRefsSrc<COEFF>::value
inline bool GrBlendCoeffRefsSrc(GrBlendCoeff coeff) {
switch (coeff) {
case kSC_GrBlendCoeff:
case kISC_GrBlendCoeff:
case kSA_GrBlendCoeff:
case kISA_GrBlendCoeff:
return true;
default:
return false;
}
}
template<GrBlendCoeff Coeff>
struct GrTBlendCoeffRefsDst : skstd::bool_constant<kDC_GrBlendCoeff == Coeff ||
kIDC_GrBlendCoeff == Coeff ||
kDA_GrBlendCoeff == Coeff ||
kIDA_GrBlendCoeff == Coeff> {};
#define GR_BLEND_COEFF_REFS_DST(COEFF) \
GrTBlendCoeffRefsDst<COEFF>::value
inline bool GrBlendCoeffRefsDst(GrBlendCoeff coeff) {
switch (coeff) {
case kDC_GrBlendCoeff:
case kIDC_GrBlendCoeff:
case kDA_GrBlendCoeff:
case kIDA_GrBlendCoeff:
return true;
default:
return false;
}
}
template<GrBlendCoeff Coeff>
struct GrTBlendCoeffRefsSrc2 : skstd::bool_constant<kS2C_GrBlendCoeff == Coeff ||
kIS2C_GrBlendCoeff == Coeff ||
kS2A_GrBlendCoeff == Coeff ||
kIS2A_GrBlendCoeff == Coeff> {};
#define GR_BLEND_COEFF_REFS_SRC2(COEFF) \
GrTBlendCoeffRefsSrc2<COEFF>::value
inline bool GrBlendCoeffRefsSrc2(GrBlendCoeff coeff) {
switch (coeff) {
case kS2C_GrBlendCoeff:
case kIS2C_GrBlendCoeff:
case kS2A_GrBlendCoeff:
case kIS2A_GrBlendCoeff:
return true;
default:
return false;
}
}
template<GrBlendCoeff SrcCoeff, GrBlendCoeff DstCoeff>
struct GrTBlendCoeffsUseSrcColor : skstd::bool_constant<kZero_GrBlendCoeff != SrcCoeff ||
GR_BLEND_COEFF_REFS_SRC(DstCoeff)> {};
#define GR_BLEND_COEFFS_USE_SRC_COLOR(SRC_COEFF, DST_COEFF) \
GrTBlendCoeffsUseSrcColor<SRC_COEFF, DST_COEFF>::value
template<GrBlendCoeff SrcCoeff, GrBlendCoeff DstCoeff>
struct GrTBlendCoeffsUseDstColor : skstd::bool_constant<GR_BLEND_COEFF_REFS_DST(SrcCoeff) ||
kZero_GrBlendCoeff != DstCoeff> {};
#define GR_BLEND_COEFFS_USE_DST_COLOR(SRC_COEFF, DST_COEFF) \
GrTBlendCoeffsUseDstColor<SRC_COEFF, DST_COEFF>::value
template<GrBlendEquation Equation>
struct GrTBlendEquationIsAdvanced : skstd::bool_constant<Equation >= kFirstAdvancedGrBlendEquation> {};
#define GR_BLEND_EQUATION_IS_ADVANCED(EQUATION) \
GrTBlendEquationIsAdvanced<EQUATION>::value
inline bool GrBlendEquationIsAdvanced(GrBlendEquation equation) {
return equation >= kFirstAdvancedGrBlendEquation;
}
template<GrBlendEquation BlendEquation, GrBlendCoeff SrcCoeff, GrBlendCoeff DstCoeff>
struct GrTBlendModifiesDst : skstd::bool_constant<
(kAdd_GrBlendEquation != BlendEquation && kReverseSubtract_GrBlendEquation != BlendEquation) ||
kZero_GrBlendCoeff != SrcCoeff ||
kOne_GrBlendCoeff != DstCoeff> {};
#define GR_BLEND_MODIFIES_DST(EQUATION, SRC_COEFF, DST_COEFF) \
GrTBlendModifiesDst<EQUATION, SRC_COEFF, DST_COEFF>::value
/**
* 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.
*/
template<GrBlendEquation Equation, GrBlendCoeff SrcCoeff, GrBlendCoeff DstCoeff>
struct GrTBlendCanTweakAlphaForCoverage : skstd::bool_constant<
GR_BLEND_EQUATION_IS_ADVANCED(Equation) ||
((kAdd_GrBlendEquation == Equation || kReverseSubtract_GrBlendEquation == Equation) &&
!GR_BLEND_COEFF_REFS_SRC(SrcCoeff) &&
(kOne_GrBlendCoeff == DstCoeff ||
kISC_GrBlendCoeff == DstCoeff ||
kISA_GrBlendCoeff == DstCoeff))> {};
#define GR_BLEND_CAN_TWEAK_ALPHA_FOR_COVERAGE(EQUATION, SRC_COEFF, DST_COEFF) \
GrTBlendCanTweakAlphaForCoverage<EQUATION, SRC_COEFF, DST_COEFF>::value
#endif
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