1
2 /*
3 * Copyright 2013 Google Inc.
4 *
5 * Use of this source code is governed by a BSD-style license that can be
6 * found in the LICENSE file.
7 */
8
9 #ifndef GrBlend_DEFINED
10 #define GrBlend_DEFINED
11
12 #include "GrColor.h"
13 #include "../private/SkTLogic.h"
14
15 /**
16 * Equations for alpha-blending.
17 */
18 enum GrBlendEquation {
19 // Basic blend equations.
20 kAdd_GrBlendEquation, //<! Cs*S + Cd*D
21 kSubtract_GrBlendEquation, //<! Cs*S - Cd*D
22 kReverseSubtract_GrBlendEquation, //<! Cd*D - Cs*S
23
24 // Advanced blend equations. These are described in the SVG and PDF specs.
25 kScreen_GrBlendEquation,
26 kOverlay_GrBlendEquation,
27 kDarken_GrBlendEquation,
28 kLighten_GrBlendEquation,
29 kColorDodge_GrBlendEquation,
30 kColorBurn_GrBlendEquation,
31 kHardLight_GrBlendEquation,
32 kSoftLight_GrBlendEquation,
33 kDifference_GrBlendEquation,
34 kExclusion_GrBlendEquation,
35 kMultiply_GrBlendEquation,
36 kHSLHue_GrBlendEquation,
37 kHSLSaturation_GrBlendEquation,
38 kHSLColor_GrBlendEquation,
39 kHSLLuminosity_GrBlendEquation,
40
41 kFirstAdvancedGrBlendEquation = kScreen_GrBlendEquation,
42 kLast_GrBlendEquation = kHSLLuminosity_GrBlendEquation
43 };
44
45 static const int kGrBlendEquationCnt = kLast_GrBlendEquation + 1;
46
47
48 /**
49 * Coefficients for alpha-blending.
50 */
51 enum GrBlendCoeff {
52 kZero_GrBlendCoeff, //<! 0
53 kOne_GrBlendCoeff, //<! 1
54 kSC_GrBlendCoeff, //<! src color
55 kISC_GrBlendCoeff, //<! one minus src color
56 kDC_GrBlendCoeff, //<! dst color
57 kIDC_GrBlendCoeff, //<! one minus dst color
58 kSA_GrBlendCoeff, //<! src alpha
59 kISA_GrBlendCoeff, //<! one minus src alpha
60 kDA_GrBlendCoeff, //<! dst alpha
61 kIDA_GrBlendCoeff, //<! one minus dst alpha
62 kConstC_GrBlendCoeff, //<! constant color
63 kIConstC_GrBlendCoeff, //<! one minus constant color
64 kConstA_GrBlendCoeff, //<! constant color alpha
65 kIConstA_GrBlendCoeff, //<! one minus constant color alpha
66 kS2C_GrBlendCoeff,
67 kIS2C_GrBlendCoeff,
68 kS2A_GrBlendCoeff,
69 kIS2A_GrBlendCoeff,
70
71 kLast_GrBlendCoeff = kIS2A_GrBlendCoeff
72 };
73
74 static const int kGrBlendCoeffCnt = kLast_GrBlendCoeff + 1;
75
76 /**
77 * Given a known blend equation in the form of srcCoeff * srcColor + dstCoeff * dstColor where
78 * there may be partial knowledge of the srcColor and dstColor component values, determine what
79 * components of the blended output color are known. Coeffs must not refer to the constant or
80 * secondary src color.
81 */
82 void GrGetCoeffBlendKnownComponents(GrBlendCoeff srcCoeff, GrBlendCoeff dstCoeff,
83 GrColor srcColor,
84 GrColorComponentFlags srcColorFlags,
85 GrColor dstColor,
86 GrColorComponentFlags dstColorFlags,
87 GrColor* outColor,
88 GrColorComponentFlags* outFlags);
89
90 template<GrBlendCoeff Coeff>
91 struct GrTBlendCoeffRefsSrc : skstd::bool_constant<kSC_GrBlendCoeff == Coeff ||
92 kISC_GrBlendCoeff == Coeff ||
93 kSA_GrBlendCoeff == Coeff ||
94 kISA_GrBlendCoeff == Coeff> {};
95
96 #define GR_BLEND_COEFF_REFS_SRC(COEFF) \
97 GrTBlendCoeffRefsSrc<COEFF>::value
98
GrBlendCoeffRefsSrc(GrBlendCoeff coeff)99 inline bool GrBlendCoeffRefsSrc(GrBlendCoeff coeff) {
100 switch (coeff) {
101 case kSC_GrBlendCoeff:
102 case kISC_GrBlendCoeff:
103 case kSA_GrBlendCoeff:
104 case kISA_GrBlendCoeff:
105 return true;
106 default:
107 return false;
108 }
109 }
110
111 template<GrBlendCoeff Coeff>
112 struct GrTBlendCoeffRefsDst : skstd::bool_constant<kDC_GrBlendCoeff == Coeff ||
113 kIDC_GrBlendCoeff == Coeff ||
114 kDA_GrBlendCoeff == Coeff ||
115 kIDA_GrBlendCoeff == Coeff> {};
116
117 #define GR_BLEND_COEFF_REFS_DST(COEFF) \
118 GrTBlendCoeffRefsDst<COEFF>::value
119
GrBlendCoeffRefsDst(GrBlendCoeff coeff)120 inline bool GrBlendCoeffRefsDst(GrBlendCoeff coeff) {
121 switch (coeff) {
122 case kDC_GrBlendCoeff:
123 case kIDC_GrBlendCoeff:
124 case kDA_GrBlendCoeff:
125 case kIDA_GrBlendCoeff:
126 return true;
127 default:
128 return false;
129 }
130 }
131
132
133 template<GrBlendCoeff Coeff>
134 struct GrTBlendCoeffRefsSrc2 : skstd::bool_constant<kS2C_GrBlendCoeff == Coeff ||
135 kIS2C_GrBlendCoeff == Coeff ||
136 kS2A_GrBlendCoeff == Coeff ||
137 kIS2A_GrBlendCoeff == Coeff> {};
138
139 #define GR_BLEND_COEFF_REFS_SRC2(COEFF) \
140 GrTBlendCoeffRefsSrc2<COEFF>::value
141
GrBlendCoeffRefsSrc2(GrBlendCoeff coeff)142 inline bool GrBlendCoeffRefsSrc2(GrBlendCoeff coeff) {
143 switch (coeff) {
144 case kS2C_GrBlendCoeff:
145 case kIS2C_GrBlendCoeff:
146 case kS2A_GrBlendCoeff:
147 case kIS2A_GrBlendCoeff:
148 return true;
149 default:
150 return false;
151 }
152 }
153
154
155 template<GrBlendCoeff SrcCoeff, GrBlendCoeff DstCoeff>
156 struct GrTBlendCoeffsUseSrcColor : skstd::bool_constant<kZero_GrBlendCoeff != SrcCoeff ||
157 GR_BLEND_COEFF_REFS_SRC(DstCoeff)> {};
158
159 #define GR_BLEND_COEFFS_USE_SRC_COLOR(SRC_COEFF, DST_COEFF) \
160 GrTBlendCoeffsUseSrcColor<SRC_COEFF, DST_COEFF>::value
161
162
163 template<GrBlendCoeff SrcCoeff, GrBlendCoeff DstCoeff>
164 struct GrTBlendCoeffsUseDstColor : skstd::bool_constant<GR_BLEND_COEFF_REFS_DST(SrcCoeff) ||
165 kZero_GrBlendCoeff != DstCoeff> {};
166
167 #define GR_BLEND_COEFFS_USE_DST_COLOR(SRC_COEFF, DST_COEFF) \
168 GrTBlendCoeffsUseDstColor<SRC_COEFF, DST_COEFF>::value
169
170
171 template<GrBlendEquation Equation>
172 struct GrTBlendEquationIsAdvanced : skstd::bool_constant<Equation >= kFirstAdvancedGrBlendEquation> {};
173
174 #define GR_BLEND_EQUATION_IS_ADVANCED(EQUATION) \
175 GrTBlendEquationIsAdvanced<EQUATION>::value
176
GrBlendEquationIsAdvanced(GrBlendEquation equation)177 inline bool GrBlendEquationIsAdvanced(GrBlendEquation equation) {
178 return equation >= kFirstAdvancedGrBlendEquation;
179 }
180
181
182 template<GrBlendEquation BlendEquation, GrBlendCoeff SrcCoeff, GrBlendCoeff DstCoeff>
183 struct GrTBlendModifiesDst : skstd::bool_constant<
184 (kAdd_GrBlendEquation != BlendEquation && kReverseSubtract_GrBlendEquation != BlendEquation) ||
185 kZero_GrBlendCoeff != SrcCoeff ||
186 kOne_GrBlendCoeff != DstCoeff> {};
187
188 #define GR_BLEND_MODIFIES_DST(EQUATION, SRC_COEFF, DST_COEFF) \
189 GrTBlendModifiesDst<EQUATION, SRC_COEFF, DST_COEFF>::value
190
191
192 /**
193 * Advanced blend equations can always tweak alpha for coverage. (See GrCustomXfermode.cpp)
194 *
195 * For "add" and "reverse subtract" the blend equation with f=coverage is:
196 *
197 * D' = f * (S * srcCoeff + D * dstCoeff) + (1-f) * D
198 * = f * S * srcCoeff + D * (f * dstCoeff + (1 - f))
199 *
200 * (Let srcCoeff be negative for reverse subtract.) We can tweak alpha for coverage when the
201 * following relationship holds:
202 *
203 * (f*S) * srcCoeff' + D * dstCoeff' == f * S * srcCoeff + D * (f * dstCoeff + (1 - f))
204 *
205 * (Where srcCoeff' and dstCoeff' have any reference to S pre-multiplied by f.)
206 *
207 * It's easy to see this works for the src term as long as srcCoeff' == srcCoeff (meaning srcCoeff
208 * does not reference S). For the dst term, this will work as long as the following is true:
209 *|
210 * dstCoeff' == f * dstCoeff + (1 - f)
211 * dstCoeff' == 1 - f * (1 - dstCoeff)
212 *
213 * By inspection we can see this will work as long as dstCoeff has a 1, and any other term in
214 * dstCoeff references S.
215 */
216 template<GrBlendEquation Equation, GrBlendCoeff SrcCoeff, GrBlendCoeff DstCoeff>
217 struct GrTBlendCanTweakAlphaForCoverage : skstd::bool_constant<
218 GR_BLEND_EQUATION_IS_ADVANCED(Equation) ||
219 ((kAdd_GrBlendEquation == Equation || kReverseSubtract_GrBlendEquation == Equation) &&
220 !GR_BLEND_COEFF_REFS_SRC(SrcCoeff) &&
221 (kOne_GrBlendCoeff == DstCoeff ||
222 kISC_GrBlendCoeff == DstCoeff ||
223 kISA_GrBlendCoeff == DstCoeff))> {};
224
225 #define GR_BLEND_CAN_TWEAK_ALPHA_FOR_COVERAGE(EQUATION, SRC_COEFF, DST_COEFF) \
226 GrTBlendCanTweakAlphaForCoverage<EQUATION, SRC_COEFF, DST_COEFF>::value
227
228 #endif
229