gfx/skia/trunk/src/core/SkMaskGamma.cpp@deefc01c0e14
gfx/skia/trunk/src/core/SkMaskGamma.cpp
Thu, 15 Jan 2015 21:03:48 +0100
- author
- Michael Schloh von Bennewitz <michael@schloh.com>
- date
- Thu, 15 Jan 2015 21:03:48 +0100
- branch
- TOR_BUG_9701
- changeset 11
- deefc01c0e14
- permissions
- -rw-r--r--
Integrate friendly tips from Tor colleagues to make (or not) 4.5 alpha 3;
This includes removal of overloaded (but unused) methods, and addition of
a overlooked call to DataStruct::SetData(nsISupports, uint32_t, bool.)
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 */
8 #include "SkTypes.h"
10 #include "SkColor.h"
11 #include "SkFloatingPoint.h"
12 #include "SkMaskGamma.h"
14 class SkLinearColorSpaceLuminance : public SkColorSpaceLuminance {
15 virtual SkScalar toLuma(SkScalar SkDEBUGCODE(gamma), SkScalar luminance) const SK_OVERRIDE {
16 SkASSERT(SK_Scalar1 == gamma);
17 return luminance;
18 }
19 virtual SkScalar fromLuma(SkScalar SkDEBUGCODE(gamma), SkScalar luma) const SK_OVERRIDE {
20 SkASSERT(SK_Scalar1 == gamma);
21 return luma;
22 }
23 };
25 class SkGammaColorSpaceLuminance : public SkColorSpaceLuminance {
26 virtual SkScalar toLuma(SkScalar gamma, SkScalar luminance) const SK_OVERRIDE {
27 return SkScalarPow(luminance, gamma);
28 }
29 virtual SkScalar fromLuma(SkScalar gamma, SkScalar luma) const SK_OVERRIDE {
30 return SkScalarPow(luma, SkScalarInvert(gamma));
31 }
32 };
34 class SkSRGBColorSpaceLuminance : public SkColorSpaceLuminance {
35 virtual SkScalar toLuma(SkScalar SkDEBUGCODE(gamma), SkScalar luminance) const SK_OVERRIDE {
36 SkASSERT(0 == gamma);
37 //The magic numbers are derived from the sRGB specification.
38 //See http://www.color.org/chardata/rgb/srgb.xalter .
39 if (luminance <= 0.04045f) {
40 return luminance / 12.92f;
41 }
42 return SkScalarPow((luminance + 0.055f) / 1.055f,
43 2.4f);
44 }
45 virtual SkScalar fromLuma(SkScalar SkDEBUGCODE(gamma), SkScalar luma) const SK_OVERRIDE {
46 SkASSERT(0 == gamma);
47 //The magic numbers are derived from the sRGB specification.
48 //See http://www.color.org/chardata/rgb/srgb.xalter .
49 if (luma <= 0.0031308f) {
50 return luma * 12.92f;
51 }
52 return 1.055f * SkScalarPow(luma, SkScalarInvert(2.4f))
53 - 0.055f;
54 }
55 };
57 /*static*/ const SkColorSpaceLuminance& SkColorSpaceLuminance::Fetch(SkScalar gamma) {
58 static SkLinearColorSpaceLuminance gSkLinearColorSpaceLuminance;
59 static SkGammaColorSpaceLuminance gSkGammaColorSpaceLuminance;
60 static SkSRGBColorSpaceLuminance gSkSRGBColorSpaceLuminance;
62 if (0 == gamma) {
63 return gSkSRGBColorSpaceLuminance;
64 } else if (SK_Scalar1 == gamma) {
65 return gSkLinearColorSpaceLuminance;
66 } else {
67 return gSkGammaColorSpaceLuminance;
68 }
69 }
71 static float apply_contrast(float srca, float contrast) {
72 return srca + ((1.0f - srca) * contrast * srca);
73 }
75 void SkTMaskGamma_build_correcting_lut(uint8_t table[256], U8CPU srcI, SkScalar contrast,
76 const SkColorSpaceLuminance& srcConvert, SkScalar srcGamma,
77 const SkColorSpaceLuminance& dstConvert, SkScalar dstGamma) {
78 const float src = (float)srcI / 255.0f;
79 const float linSrc = srcConvert.toLuma(srcGamma, src);
80 //Guess at the dst. The perceptual inverse provides smaller visual
81 //discontinuities when slight changes to desaturated colors cause a channel
82 //to map to a different correcting lut with neighboring srcI.
83 //See https://code.google.com/p/chromium/issues/detail?id=141425#c59 .
84 const float dst = 1.0f - src;
85 const float linDst = dstConvert.toLuma(dstGamma, dst);
87 //Contrast value tapers off to 0 as the src luminance becomes white
88 const float adjustedContrast = SkScalarToFloat(contrast) * linDst;
90 //Remove discontinuity and instability when src is close to dst.
91 //The value 1/256 is arbitrary and appears to contain the instability.
92 if (fabs(src - dst) < (1.0f / 256.0f)) {
93 float ii = 0.0f;
94 for (int i = 0; i < 256; ++i, ii += 1.0f) {
95 float rawSrca = ii / 255.0f;
96 float srca = apply_contrast(rawSrca, adjustedContrast);
97 table[i] = SkToU8(sk_float_round2int(255.0f * srca));
98 }
99 } else {
100 // Avoid slow int to float conversion.
101 float ii = 0.0f;
102 for (int i = 0; i < 256; ++i, ii += 1.0f) {
103 // 'rawSrca += 1.0f / 255.0f' and even
104 // 'rawSrca = i * (1.0f / 255.0f)' can add up to more than 1.0f.
105 // When this happens the table[255] == 0x0 instead of 0xff.
106 // See http://code.google.com/p/chromium/issues/detail?id=146466
107 float rawSrca = ii / 255.0f;
108 float srca = apply_contrast(rawSrca, adjustedContrast);
109 SkASSERT(srca <= 1.0f);
110 float dsta = 1.0f - srca;
112 //Calculate the output we want.
113 float linOut = (linSrc * srca + dsta * linDst);
114 SkASSERT(linOut <= 1.0f);
115 float out = dstConvert.fromLuma(dstGamma, linOut);
117 //Undo what the blit blend will do.
118 float result = (out - dst) / (src - dst);
119 SkASSERT(sk_float_round2int(255.0f * result) <= 255);
121 table[i] = SkToU8(sk_float_round2int(255.0f * result));
122 }
123 }
124 }
