1 /*
2 * Copyright 2012 Google Inc.
3 *
4 * Use of this source code is governed by a BSD-style license that can be
5 * found in the LICENSE file.
6 */
7
8 #ifndef SkMaskGamma_DEFINED
9 #define SkMaskGamma_DEFINED
10
11 #include "SkColor.h"
12 #include "SkColorData.h"
13 #include "SkNoncopyable.h"
14 #include "SkRefCnt.h"
15 #include "SkTypes.h"
16
17 /**
18 * SkColorSpaceLuminance is used to convert luminances to and from linear and
19 * perceptual color spaces.
20 *
21 * Luma is used to specify a linear luminance value [0.0, 1.0].
22 * Luminance is used to specify a luminance value in an arbitrary color space [0.0, 1.0].
23 */
24 class SkColorSpaceLuminance : SkNoncopyable {
25 public:
~SkColorSpaceLuminance()26 virtual ~SkColorSpaceLuminance() { }
27
28 /** Converts a color component luminance in the color space to a linear luma. */
29 virtual SkScalar toLuma(SkScalar gamma, SkScalar luminance) const = 0;
30 /** Converts a linear luma to a color component luminance in the color space. */
31 virtual SkScalar fromLuma(SkScalar gamma, SkScalar luma) const = 0;
32
33 /** Converts a color to a luminance value. */
computeLuminance(SkScalar gamma,SkColor c)34 static U8CPU computeLuminance(SkScalar gamma, SkColor c) {
35 const SkColorSpaceLuminance& luminance = Fetch(gamma);
36 SkScalar r = luminance.toLuma(gamma, SkIntToScalar(SkColorGetR(c)) / 255);
37 SkScalar g = luminance.toLuma(gamma, SkIntToScalar(SkColorGetG(c)) / 255);
38 SkScalar b = luminance.toLuma(gamma, SkIntToScalar(SkColorGetB(c)) / 255);
39 SkScalar luma = r * SK_LUM_COEFF_R +
40 g * SK_LUM_COEFF_G +
41 b * SK_LUM_COEFF_B;
42 SkASSERT(luma <= SK_Scalar1);
43 return SkScalarRoundToInt(luminance.fromLuma(gamma, luma) * 255);
44 }
45
46 /** Retrieves the SkColorSpaceLuminance for the given gamma. */
47 static const SkColorSpaceLuminance& Fetch(SkScalar gamma);
48 };
49
50 ///@{
51 /**
52 * Scales base <= 2^N-1 to 2^8-1
53 * @param N [1, 8] the number of bits used by base.
54 * @param base the number to be scaled to [0, 255].
55 */
sk_t_scale255(U8CPU base)56 template<U8CPU N> static inline U8CPU sk_t_scale255(U8CPU base) {
57 base <<= (8 - N);
58 U8CPU lum = base;
59 for (unsigned int i = N; i < 8; i += N) {
60 lum |= base >> i;
61 }
62 return lum;
63 }
64 template<> /*static*/ inline U8CPU sk_t_scale255<1>(U8CPU base) {
65 return base * 0xFF;
66 }
67 template<> /*static*/ inline U8CPU sk_t_scale255<2>(U8CPU base) {
68 return base * 0x55;
69 }
70 template<> /*static*/ inline U8CPU sk_t_scale255<4>(U8CPU base) {
71 return base * 0x11;
72 }
73 template<> /*static*/ inline U8CPU sk_t_scale255<8>(U8CPU base) {
74 return base;
75 }
76 ///@}
77
78 template <int R_LUM_BITS, int G_LUM_BITS, int B_LUM_BITS> class SkTMaskPreBlend;
79
80 void SkTMaskGamma_build_correcting_lut(uint8_t table[256], U8CPU srcI, SkScalar contrast,
81 const SkColorSpaceLuminance& srcConvert, SkScalar srcGamma,
82 const SkColorSpaceLuminance& dstConvert, SkScalar dstGamma);
83
84 /**
85 * A regular mask contains linear alpha values. A gamma correcting mask
86 * contains non-linear alpha values in an attempt to create gamma correct blits
87 * in the presence of a gamma incorrect (linear) blend in the blitter.
88 *
89 * SkMaskGamma creates and maintains tables which convert linear alpha values
90 * to gamma correcting alpha values.
91 * @param R The number of luminance bits to use [1, 8] from the red channel.
92 * @param G The number of luminance bits to use [1, 8] from the green channel.
93 * @param B The number of luminance bits to use [1, 8] from the blue channel.
94 */
95 template <int R_LUM_BITS, int G_LUM_BITS, int B_LUM_BITS> class SkTMaskGamma : public SkRefCnt {
96
97 public:
98
99 /** Creates a linear SkTMaskGamma. */
SkTMaskGamma()100 SkTMaskGamma() : fIsLinear(true) { }
101
102 /**
103 * Creates tables to convert linear alpha values to gamma correcting alpha
104 * values.
105 *
106 * @param contrast A value in the range [0.0, 1.0] which indicates the
107 * amount of artificial contrast to add.
108 * @param paint The color space in which the paint color was chosen.
109 * @param device The color space of the target device.
110 */
SkTMaskGamma(SkScalar contrast,SkScalar paintGamma,SkScalar deviceGamma)111 SkTMaskGamma(SkScalar contrast, SkScalar paintGamma, SkScalar deviceGamma) : fIsLinear(false) {
112 const SkColorSpaceLuminance& paintConvert = SkColorSpaceLuminance::Fetch(paintGamma);
113 const SkColorSpaceLuminance& deviceConvert = SkColorSpaceLuminance::Fetch(deviceGamma);
114 for (U8CPU i = 0; i < (1 << MAX_LUM_BITS); ++i) {
115 U8CPU lum = sk_t_scale255<MAX_LUM_BITS>(i);
116 SkTMaskGamma_build_correcting_lut(fGammaTables[i], lum, contrast,
117 paintConvert, paintGamma,
118 deviceConvert, deviceGamma);
119 }
120 }
121
122 /** Given a color, returns the closest canonical color. */
CanonicalColor(SkColor color)123 static SkColor CanonicalColor(SkColor color) {
124 return SkColorSetRGB(
125 sk_t_scale255<R_LUM_BITS>(SkColorGetR(color) >> (8 - R_LUM_BITS)),
126 sk_t_scale255<G_LUM_BITS>(SkColorGetG(color) >> (8 - G_LUM_BITS)),
127 sk_t_scale255<B_LUM_BITS>(SkColorGetB(color) >> (8 - B_LUM_BITS)));
128 }
129
130 /** The type of the mask pre-blend which will be returned from preBlend(SkColor). */
131 typedef SkTMaskPreBlend<R_LUM_BITS, G_LUM_BITS, B_LUM_BITS> PreBlend;
132
133 /**
134 * Provides access to the tables appropriate for converting linear alpha
135 * values into gamma correcting alpha values when drawing the given color
136 * through the mask. The destination color will be approximated.
137 */
138 PreBlend preBlend(SkColor color) const;
139
140 /**
141 * Get dimensions for the full table set, so it can be allocated as a block.
142 */
getGammaTableDimensions(int * tableWidth,int * numTables)143 void getGammaTableDimensions(int* tableWidth, int* numTables) const {
144 *tableWidth = 256;
145 *numTables = (1 << MAX_LUM_BITS);
146 }
147
148 /**
149 * Provides direct access to the full table set, so it can be uploaded
150 * into a texture or analyzed in other ways.
151 * Returns nullptr if fGammaTables hasn't been initialized.
152 */
getGammaTables()153 const uint8_t* getGammaTables() const {
154 return fIsLinear ? nullptr : (const uint8_t*) fGammaTables;
155 }
156
157 private:
158 static const int MAX_LUM_BITS =
159 B_LUM_BITS > (R_LUM_BITS > G_LUM_BITS ? R_LUM_BITS : G_LUM_BITS)
160 ? B_LUM_BITS : (R_LUM_BITS > G_LUM_BITS ? R_LUM_BITS : G_LUM_BITS);
161 uint8_t fGammaTables[1 << MAX_LUM_BITS][256];
162 bool fIsLinear;
163
164 typedef SkRefCnt INHERITED;
165 };
166
167
168 /**
169 * SkTMaskPreBlend is a tear-off of SkTMaskGamma. It provides the tables to
170 * convert a linear alpha value for a given channel to a gamma correcting alpha
171 * value for that channel. This class is immutable.
172 *
173 * If fR, fG, or fB is nullptr, all of them will be. This indicates that no mask
174 * pre blend should be applied. SkTMaskPreBlend::isApplicable() is provided as
175 * a convenience function to test for the absence of this case.
176 */
177 template <int R_LUM_BITS, int G_LUM_BITS, int B_LUM_BITS> class SkTMaskPreBlend {
178 private:
SkTMaskPreBlend(sk_sp<const SkTMaskGamma<R_LUM_BITS,G_LUM_BITS,B_LUM_BITS>> parent,const uint8_t * r,const uint8_t * g,const uint8_t * b)179 SkTMaskPreBlend(sk_sp<const SkTMaskGamma<R_LUM_BITS, G_LUM_BITS, B_LUM_BITS>> parent,
180 const uint8_t* r, const uint8_t* g, const uint8_t* b)
181 : fParent(std::move(parent)), fR(r), fG(g), fB(b) { }
182
183 sk_sp<const SkTMaskGamma<R_LUM_BITS, G_LUM_BITS, B_LUM_BITS>> fParent;
184 friend class SkTMaskGamma<R_LUM_BITS, G_LUM_BITS, B_LUM_BITS>;
185 public:
186 /** Creates a non applicable SkTMaskPreBlend. */
SkTMaskPreBlend()187 SkTMaskPreBlend() : fParent(), fR(nullptr), fG(nullptr), fB(nullptr) { }
188
189 /**
190 * This copy contructor exists for correctness, but should never be called
191 * when return value optimization is enabled.
192 */
SkTMaskPreBlend(const SkTMaskPreBlend<R_LUM_BITS,G_LUM_BITS,B_LUM_BITS> & that)193 SkTMaskPreBlend(const SkTMaskPreBlend<R_LUM_BITS, G_LUM_BITS, B_LUM_BITS>& that)
194 : fParent(that.fParent), fR(that.fR), fG(that.fG), fB(that.fB) { }
195
~SkTMaskPreBlend()196 ~SkTMaskPreBlend() { }
197
198 /** True if this PreBlend should be applied. When false, fR, fG, and fB are nullptr. */
isApplicable()199 bool isApplicable() const { return SkToBool(this->fG); }
200
201 const uint8_t* fR;
202 const uint8_t* fG;
203 const uint8_t* fB;
204 };
205
206 template <int R_LUM_BITS, int G_LUM_BITS, int B_LUM_BITS>
207 SkTMaskPreBlend<R_LUM_BITS, G_LUM_BITS, B_LUM_BITS>
preBlend(SkColor color)208 SkTMaskGamma<R_LUM_BITS, G_LUM_BITS, B_LUM_BITS>::preBlend(SkColor color) const {
209 return fIsLinear ? SkTMaskPreBlend<R_LUM_BITS, G_LUM_BITS, B_LUM_BITS>()
210 : SkTMaskPreBlend<R_LUM_BITS, G_LUM_BITS, B_LUM_BITS>(sk_ref_sp(this),
211 fGammaTables[SkColorGetR(color) >> (8 - MAX_LUM_BITS)],
212 fGammaTables[SkColorGetG(color) >> (8 - MAX_LUM_BITS)],
213 fGammaTables[SkColorGetB(color) >> (8 - MAX_LUM_BITS)]);
214 }
215
216 ///@{
217 /**
218 * If APPLY_LUT is false, returns component unchanged.
219 * If APPLY_LUT is true, returns lut[component].
220 * @param APPLY_LUT whether or not the look-up table should be applied to component.
221 * @component the initial component.
222 * @lut a look-up table which transforms the component.
223 */
sk_apply_lut_if(U8CPU component,const uint8_t *)224 template<bool APPLY_LUT> static inline U8CPU sk_apply_lut_if(U8CPU component, const uint8_t*) {
225 return component;
226 }
227 template<> /*static*/ inline U8CPU sk_apply_lut_if<true>(U8CPU component, const uint8_t* lut) {
228 return lut[component];
229 }
230 ///@}
231
232 #endif
233