chromium/third_party/skia/src/core/SkMaskGamma.h

/*
 * 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 "include/core/SkColor.h"
#include "include/core/SkRefCnt.h"
#include "include/core/SkScalar.h"
#include "include/core/SkTypes.h"
#include "include/private/SkColorData.h"
#include "include/private/base/SkCPUTypes.h"
#include "include/private/base/SkNoncopyable.h"
#include "include/private/base/SkTo.h"

#include <algorithm>
#include <cstddef>
#include <cstdint>
#include <memory>

/**
 * 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 { … };

///@{
/**
 * 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) { … }
template<> /*static*/ inline U8CPU sk_t_scale255<1>(U8CPU base) { … }
template<> /*static*/ inline U8CPU sk_t_scale255<2>(U8CPU base) { … }
template<> /*static*/ inline U8CPU sk_t_scale255<4>(U8CPU base) { … }
template<> /*static*/ inline U8CPU sk_t_scale255<8>(U8CPU base) { … }
///@}

template <int R_LUM_BITS, int G_LUM_BITS, int B_LUM_BITS> class SkTMaskPreBlend;

void SkTMaskGamma_build_correcting_lut(uint8_t* table, U8CPU srcI, SkScalar contrast,
                                       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 { … };

/**
 * 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 nullptr, 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 { … };

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 { … }

///@{
/**
 *  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*) { … }
template<> /*static*/ inline U8CPU sk_apply_lut_if<true>(U8CPU component, const uint8_t* lut) { … }
///@}

#endif