The Tor Browser: gfx/skia/trunk/src/core/SkMaskGamma.cpp@6474c204b198 (annotated)

gfx/skia/trunk/src/core/SkMaskGamma.cpp@6474c204b198 (annotated)

gfx/skia/trunk/src/core/SkMaskGamma.cpp

Wed, 31 Dec 2014 06:09:35 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Wed, 31 Dec 2014 06:09:35 +0100
changeset 0: 6474c204b198
permissions: -rw-r--r--

Cloned upstream origin tor-browser at tor-browser-31.3.0esr-4.5-1-build1
revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #include "SkTypes.h"
 #include "SkColor.h"
 #include "SkFloatingPoint.h"
 #include "SkMaskGamma.h"
 class SkLinearColorSpaceLuminance : public SkColorSpaceLuminance {
     virtual SkScalar toLuma(SkScalar SkDEBUGCODE(gamma), SkScalar luminance) const SK_OVERRIDE {
         SkASSERT(SK_Scalar1 == gamma);
         return luminance;
     }
     virtual SkScalar fromLuma(SkScalar SkDEBUGCODE(gamma), SkScalar luma) const SK_OVERRIDE {
         SkASSERT(SK_Scalar1 == gamma);
         return luma;
     }
 };
 class SkGammaColorSpaceLuminance : public SkColorSpaceLuminance {
     virtual SkScalar toLuma(SkScalar gamma, SkScalar luminance) const SK_OVERRIDE {
         return SkScalarPow(luminance, gamma);
     }
     virtual SkScalar fromLuma(SkScalar gamma, SkScalar luma) const SK_OVERRIDE {
         return SkScalarPow(luma, SkScalarInvert(gamma));
     }
 };
 class SkSRGBColorSpaceLuminance : public SkColorSpaceLuminance {
     virtual SkScalar toLuma(SkScalar SkDEBUGCODE(gamma), SkScalar luminance) const SK_OVERRIDE {
         SkASSERT(0 == gamma);
         //The magic numbers are derived from the sRGB specification.
         //See http://www.color.org/chardata/rgb/srgb.xalter .
         if (luminance <= 0.04045f) {
             return luminance / 12.92f;
         }
         return SkScalarPow((luminance + 0.055f) / 1.055f,
 .4f);
     }
     virtual SkScalar fromLuma(SkScalar SkDEBUGCODE(gamma), SkScalar luma) const SK_OVERRIDE {
         SkASSERT(0 == gamma);
         //The magic numbers are derived from the sRGB specification.
         //See http://www.color.org/chardata/rgb/srgb.xalter .
         if (luma <= 0.0031308f) {
             return luma * 12.92f;
         }
         return 1.055f * SkScalarPow(luma, SkScalarInvert(2.4f))
                - 0.055f;
     }
 };
 /*static*/ const SkColorSpaceLuminance& SkColorSpaceLuminance::Fetch(SkScalar gamma) {
     static SkLinearColorSpaceLuminance gSkLinearColorSpaceLuminance;
     static SkGammaColorSpaceLuminance gSkGammaColorSpaceLuminance;
     static SkSRGBColorSpaceLuminance gSkSRGBColorSpaceLuminance;
     if (0 == gamma) {
         return gSkSRGBColorSpaceLuminance;
     } else if (SK_Scalar1 == gamma) {
         return gSkLinearColorSpaceLuminance;
     } else {
         return gSkGammaColorSpaceLuminance;
     }
 }
 static float apply_contrast(float srca, float contrast) {
     return srca + ((1.0f - srca) * contrast * srca);
 }
 void SkTMaskGamma_build_correcting_lut(uint8_t table[256], U8CPU srcI, SkScalar contrast,
                                        const SkColorSpaceLuminance& srcConvert, SkScalar srcGamma,
                                        const SkColorSpaceLuminance& dstConvert, SkScalar dstGamma) {
     const float src = (float)srcI / 255.0f;
     const float linSrc = srcConvert.toLuma(srcGamma, src);
     //Guess at the dst. The perceptual inverse provides smaller visual
     //discontinuities when slight changes to desaturated colors cause a channel
     //to map to a different correcting lut with neighboring srcI.
     //See https://code.google.com/p/chromium/issues/detail?id=141425#c59 .
     const float dst = 1.0f - src;
     const float linDst = dstConvert.toLuma(dstGamma, dst);
     //Contrast value tapers off to 0 as the src luminance becomes white
     const float adjustedContrast = SkScalarToFloat(contrast) * linDst;
     //Remove discontinuity and instability when src is close to dst.
     //The value 1/256 is arbitrary and appears to contain the instability.
     if (fabs(src - dst) < (1.0f / 256.0f)) {
         float ii = 0.0f;
         for (int i = 0; i < 256; ++i, ii += 1.0f) {
             float rawSrca = ii / 255.0f;
             float srca = apply_contrast(rawSrca, adjustedContrast);
             table[i] = SkToU8(sk_float_round2int(255.0f * srca));
         }
     } else {
         // Avoid slow int to float conversion.
         float ii = 0.0f;
         for (int i = 0; i < 256; ++i, ii += 1.0f) {
             // 'rawSrca += 1.0f / 255.0f' and even
             // 'rawSrca = i * (1.0f / 255.0f)' can add up to more than 1.0f.
             // When this happens the table[255] == 0x0 instead of 0xff.
             // See http://code.google.com/p/chromium/issues/detail?id=146466
             float rawSrca = ii / 255.0f;
             float srca = apply_contrast(rawSrca, adjustedContrast);
             SkASSERT(srca <= 1.0f);
             float dsta = 1.0f - srca;
             //Calculate the output we want.
             float linOut = (linSrc * srca + dsta * linDst);
             SkASSERT(linOut <= 1.0f);
             float out = dstConvert.fromLuma(dstGamma, linOut);
             //Undo what the blit blend will do.
             float result = (out - dst) / (src - dst);
             SkASSERT(sk_float_round2int(255.0f * result) <= 255);
             table[i] = SkToU8(sk_float_round2int(255.0f * result));
         }
     }
 }

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gfx/skia/trunk/src/core/SkMaskGamma.cpp@6474c204b198 (annotated)

gfx/skia/trunk/src/core/SkMaskGamma.cpp