1 files changed, 125 insertions, 0 deletions
diff --git a/gfx/skia/skia/src/core/SkMaskGamma.cpp b/gfx/skia/skia/src/core/SkMaskGamma.cpp
new file mode 100644
index 0000000000..5c82c5e7a8
--- /dev/null
+++ b/gfx/skia/skia/src/core/SkMaskGamma.cpp
@@ -0,0 +1,125 @@
+/*
+ * 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 "src/core/SkMaskGamma.h"
+
+#include "include/core/SkColor.h"
+#include "include/core/SkTypes.h"
+#include "include/private/base/SkFloatingPoint.h"
+#include "include/private/base/SkTo.h"
+
+class SkLinearColorSpaceLuminance : public SkColorSpaceLuminance {
+    SkScalar toLuma(SkScalar SkDEBUGCODE(gamma), SkScalar luminance) const override {
+        SkASSERT(SK_Scalar1 == gamma);
+        return luminance;
+    }
+    SkScalar fromLuma(SkScalar SkDEBUGCODE(gamma), SkScalar luma) const override {
+        SkASSERT(SK_Scalar1 == gamma);
+        return luma;
+    }
+};
+
+class SkGammaColorSpaceLuminance : public SkColorSpaceLuminance {
+    SkScalar toLuma(SkScalar gamma, SkScalar luminance) const override {
+        return SkScalarPow(luminance, gamma);
+    }
+    SkScalar fromLuma(SkScalar gamma, SkScalar luma) const override {
+        return SkScalarPow(luma, SkScalarInvert(gamma));
+    }
+};
+
+class SkSRGBColorSpaceLuminance : public SkColorSpaceLuminance {
+    SkScalar toLuma(SkScalar SkDEBUGCODE(gamma), SkScalar luminance) const 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,
+                        2.4f);
+    }
+    SkScalar fromLuma(SkScalar SkDEBUGCODE(gamma), SkScalar luma) const 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));
+        }
+    }
+}