| /* |
| * 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 { |
| |
| 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; |
| |
| /** |
| * Get dimensions for the full table set, so it can be allocated as a block. |
| */ |
| void getGammaTableDimensions(int* tableWidth, int* numTables) const { |
| *tableWidth = 256; |
| *numTables = (1 << MAX_LUM_BITS); |
| } |
| |
| /** |
| * Provides direct access to the full table set, so it can be uploaded |
| * into a texture. |
| */ |
| const uint8_t* getGammaTables() const { |
| return (const uint8_t*) fGammaTables; |
| } |
| |
| 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 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 { |
| private: |
| SkTMaskPreBlend(sk_sp<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(std::move(parent)), fR(r), fG(g), fB(b) { } |
| |
| sk_sp<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(nullptr), fG(nullptr), fB(nullptr) { } |
| |
| /** |
| * 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(that.fParent), fR(that.fR), fG(that.fG), fB(that.fB) { } |
| |
| ~SkTMaskPreBlend() { } |
| |
| /** True if this PreBlend should be applied. When false, fR, fG, and fB are nullptr. */ |
| bool isApplicable() const { return SkToBool(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>(sk_ref_sp(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 |