The Tor Browser: comparison gfx/skia/trunk/src/core/SkMaskGamma.h

--1:000000000000
+:77b11c2b6b84
+/*
+* Copyright 2012 Google Inc.
+*
+* Use of this source code is governed by a BSD-style license that can be
+* found in the LICENSE file.
+*/
+#ifndef SkMaskGamma_DEFINED
+#define SkMaskGamma_DEFINED
+#include "SkTypes.h"
+#include "SkColor.h"
+#include "SkColorPriv.h"
+#include "SkRefCnt.h"
+/**
+* SkColorSpaceLuminance is used to convert luminances to and from linear and
+* perceptual color spaces.
+*
+* Luma is used to specify a linear luminance value [0.0, 1.0].
+* Luminance is used to specify a luminance value in an arbitrary color space [0.0, 1.0].
+*/
+class SkColorSpaceLuminance : SkNoncopyable {
+public:
+virtual ~SkColorSpaceLuminance() { }
+/** Converts a color component luminance in the color space to a linear luma. */
+virtual SkScalar toLuma(SkScalar gamma, SkScalar luminance) const = 0;
+/** Converts a linear luma to a color component luminance in the color space. */
+virtual SkScalar fromLuma(SkScalar gamma, SkScalar luma) const = 0;
+/** Converts a color to a luminance value. */
+static U8CPU computeLuminance(SkScalar gamma, SkColor c) {
+const SkColorSpaceLuminance& luminance = Fetch(gamma);
+SkScalar r = luminance.toLuma(gamma, SkIntToScalar(SkColorGetR(c)) / 255);
+SkScalar g = luminance.toLuma(gamma, SkIntToScalar(SkColorGetG(c)) / 255);
+SkScalar b = luminance.toLuma(gamma, SkIntToScalar(SkColorGetB(c)) / 255);
+SkScalar luma = r * SK_LUM_COEFF_R +
+g * SK_LUM_COEFF_G +
+b * SK_LUM_COEFF_B;
+SkASSERT(luma <= SK_Scalar1);
+return SkScalarRoundToInt(luminance.fromLuma(gamma, luma) * 255);
+}
+/** Retrieves the SkColorSpaceLuminance for the given gamma. */
+static const SkColorSpaceLuminance& Fetch(SkScalar gamma);
+};
+///@{
+/**
+* Scales base <= 2^N-1 to 2^8-1
+* @param N [1, 8] the number of bits used by base.
+* @param base the number to be scaled to [0, 255].
+*/
+template<U8CPU N> static inline U8CPU sk_t_scale255(U8CPU base) {
+base <<= (8 - N);
+U8CPU lum = base;
+for (unsigned int i = N; i < 8; i += N) {
+lum |= base >> i;
+}
+return lum;
+}
+template<> /*static*/ inline U8CPU sk_t_scale255<1>(U8CPU base) {
+return base * 0xFF;
+}
+template<> /*static*/ inline U8CPU sk_t_scale255<2>(U8CPU base) {
+return base * 0x55;
+}
+template<> /*static*/ inline U8CPU sk_t_scale255<4>(U8CPU base) {
+return base * 0x11;
+}
+template<> /*static*/ inline U8CPU sk_t_scale255<8>(U8CPU base) {
+return base;
+}
+///@}
+template <int R_LUM_BITS, int G_LUM_BITS, int B_LUM_BITS> class SkTMaskPreBlend;
+void SkTMaskGamma_build_correcting_lut(uint8_t table[256], U8CPU srcI, SkScalar contrast,
+const SkColorSpaceLuminance& srcConvert, SkScalar srcGamma,
+const SkColorSpaceLuminance& dstConvert, SkScalar dstGamma);
+/**
+* A regular mask contains linear alpha values. A gamma correcting mask
+* contains non-linear alpha values in an attempt to create gamma correct blits
+* in the presence of a gamma incorrect (linear) blend in the blitter.
+*
+* SkMaskGamma creates and maintains tables which convert linear alpha values
+* to gamma correcting alpha values.
+* @param R The number of luminance bits to use [1, 8] from the red channel.
+* @param G The number of luminance bits to use [1, 8] from the green channel.
+* @param B The number of luminance bits to use [1, 8] from the blue channel.
+*/
+template <int R_LUM_BITS, int G_LUM_BITS, int B_LUM_BITS> class SkTMaskGamma : public SkRefCnt {
+SK_DECLARE_INST_COUNT(SkTMaskGamma)
+public:
+/** Creates a linear SkTMaskGamma. */
+SkTMaskGamma() : fIsLinear(true) { }
+/**
+* Creates tables to convert linear alpha values to gamma correcting alpha
+* values.
+*
+* @param contrast A value in the range [0.0, 1.0] which indicates the
+*                 amount of artificial contrast to add.
+* @param paint The color space in which the paint color was chosen.
+* @param device The color space of the target device.
+*/
+SkTMaskGamma(SkScalar contrast, SkScalar paintGamma, SkScalar deviceGamma) : fIsLinear(false) {
+const SkColorSpaceLuminance& paintConvert = SkColorSpaceLuminance::Fetch(paintGamma);
+const SkColorSpaceLuminance& deviceConvert = SkColorSpaceLuminance::Fetch(deviceGamma);
+for (U8CPU i = 0; i < (1 << MAX_LUM_BITS); ++i) {
+U8CPU lum = sk_t_scale255<MAX_LUM_BITS>(i);
+SkTMaskGamma_build_correcting_lut(fGammaTables[i], lum, contrast,
+paintConvert, paintGamma,
+deviceConvert, deviceGamma);
+}
+}
+/** Given a color, returns the closest canonical color. */
+static SkColor CanonicalColor(SkColor color) {
+return SkColorSetRGB(
+sk_t_scale255<R_LUM_BITS>(SkColorGetR(color) >> (8 - R_LUM_BITS)),
+sk_t_scale255<G_LUM_BITS>(SkColorGetG(color) >> (8 - G_LUM_BITS)),
+sk_t_scale255<B_LUM_BITS>(SkColorGetB(color) >> (8 - B_LUM_BITS)));
+}
+/** The type of the mask pre-blend which will be returned from preBlend(SkColor). */
+typedef SkTMaskPreBlend<R_LUM_BITS, G_LUM_BITS, B_LUM_BITS> PreBlend;
+/**
+* Provides access to the tables appropriate for converting linear alpha
+* values into gamma correcting alpha values when drawing the given color
+* through the mask. The destination color will be approximated.
+*/
+PreBlend preBlend(SkColor color) const;
+private:
+static const int MAX_LUM_BITS =
+B_LUM_BITS > (R_LUM_BITS > G_LUM_BITS ? R_LUM_BITS : G_LUM_BITS)
+? B_LUM_BITS : (R_LUM_BITS > G_LUM_BITS ? R_LUM_BITS : G_LUM_BITS);
+uint8_t fGammaTables[1 << MAX_LUM_BITS][256];
+bool fIsLinear;
+typedef SkRefCnt INHERITED;
+};
+/**
+* SkTMaskPreBlend is a tear-off of SkTMaskGamma. It provides the tables to
+* convert a linear alpha value for a given channel to a gamma correcting alpha
+* value for that channel. This class is immutable.
+*
+* If fR, fG, or fB is NULL, all of them will be. This indicates that no mask
+* pre blend should be applied. SkTMaskPreBlend::isApplicable() is provided as
+* a convenience function to test for the absence of this case.
+*/
+template <int R_LUM_BITS, int G_LUM_BITS, int B_LUM_BITS> class SkTMaskPreBlend {
+private:
+SkTMaskPreBlend(const SkTMaskGamma<R_LUM_BITS, G_LUM_BITS, B_LUM_BITS>* parent,
+const uint8_t* r, const uint8_t* g, const uint8_t* b)
+: fParent(SkSafeRef(parent)), fR(r), fG(g), fB(b) { }
+SkAutoTUnref<const SkTMaskGamma<R_LUM_BITS, G_LUM_BITS, B_LUM_BITS> > fParent;
+friend class SkTMaskGamma<R_LUM_BITS, G_LUM_BITS, B_LUM_BITS>;
+public:
+/** Creates a non applicable SkTMaskPreBlend. */
+SkTMaskPreBlend() : fParent(), fR(NULL), fG(NULL), fB(NULL) { }
+/**
+* This copy contructor exists for correctness, but should never be called
+* when return value optimization is enabled.
+*/
+SkTMaskPreBlend(const SkTMaskPreBlend<R_LUM_BITS, G_LUM_BITS, B_LUM_BITS>& that)
+: fParent(SkSafeRef(that.fParent.get())), fR(that.fR), fG(that.fG), fB(that.fB) { }
+~SkTMaskPreBlend() { }
+/** True if this PreBlend should be applied. When false, fR, fG, and fB are NULL. */
+bool isApplicable() const {
+return NULL != this->fG;
+}
+const uint8_t* fR;
+const uint8_t* fG;
+const uint8_t* fB;
+};
+template <int R_LUM_BITS, int G_LUM_BITS, int B_LUM_BITS>
+SkTMaskPreBlend<R_LUM_BITS, G_LUM_BITS, B_LUM_BITS>
+SkTMaskGamma<R_LUM_BITS, G_LUM_BITS, B_LUM_BITS>::preBlend(SkColor color) const {
+return fIsLinear ? SkTMaskPreBlend<R_LUM_BITS, G_LUM_BITS, B_LUM_BITS>()
+: SkTMaskPreBlend<R_LUM_BITS, G_LUM_BITS, B_LUM_BITS>(this,
+fGammaTables[SkColorGetR(color) >> (8 - MAX_LUM_BITS)],
+fGammaTables[SkColorGetG(color) >> (8 - MAX_LUM_BITS)],
+fGammaTables[SkColorGetB(color) >> (8 - MAX_LUM_BITS)]);
+}
+///@{
+/**
+*  If APPLY_LUT is false, returns component unchanged.
+*  If APPLY_LUT is true, returns lut[component].
+*  @param APPLY_LUT whether or not the look-up table should be applied to component.
+*  @component the initial component.
+*  @lut a look-up table which transforms the component.
+*/
+template<bool APPLY_LUT> static inline U8CPU sk_apply_lut_if(U8CPU component, const uint8_t*) {
+return component;
+}
+template<> /*static*/ inline U8CPU sk_apply_lut_if<true>(U8CPU component, const uint8_t* lut) {
+return lut[component];
+}
+///@}
+#endif

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comparison: gfx/skia/trunk/src/core/SkMaskGamma.h

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