effects/SkLumaXfermode.cpp

/*
 * Copyright 2013 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#include "SkLumaXfermode.h"
#include "SkColorPriv.h"
#include "SkFlattenableBuffers.h"
#include "SkString.h"

#if SK_SUPPORT_GPU
#include "gl/GrGLEffect.h"
#include "GrContext.h"
#include "GrTBackendEffectFactory.h"
#endif

class SkLumaMaskXfermodeSrcOver : public SkLumaMaskXfermode {
public:
    SkLumaMaskXfermodeSrcOver();

    SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkLumaMaskXfermodeSrcOver)

protected:
    SkLumaMaskXfermodeSrcOver(SkFlattenableReadBuffer&);

private:
    typedef SkLumaMaskXfermode INHERITED;

    virtual SkPMColor lumaProc(const SkPMColor a, const SkPMColor b) const;
};

SkPMColor SkLumaMaskXfermode::lumaProc(const SkPMColor a, const SkPMColor b) const {
    unsigned luma = SkComputeLuminance(SkGetPackedR32(b),
                                       SkGetPackedG32(b),
                                       SkGetPackedB32(b));
    return SkAlphaMulQ(a, SkAlpha255To256(luma));
}

template <typename T>
static inline const T* lumaOpA(SkXfermode::Mode mode,
                               const T* src, const T* dst) {
    return SkXfermode::kSrcIn_Mode == mode ? src : dst;
}

template <typename T>
static inline const T* lumaOpB(SkXfermode::Mode mode,
                               const T* src, const T* dst) {
    return SkXfermode::kSrcIn_Mode == mode ? dst : src;
}

SkXfermode* SkLumaMaskXfermode::Create(SkXfermode::Mode mode) {
    if (kSrcIn_Mode == mode || kDstIn_Mode == mode) {
        return SkNEW_ARGS(SkLumaMaskXfermode, (mode));
    }
    if (kSrcOver_Mode == mode) {
        return SkNEW_ARGS(SkLumaMaskXfermodeSrcOver, ());
    }

    return NULL;
}

SkLumaMaskXfermode::SkLumaMaskXfermode(SkXfermode::Mode mode)
    : fMode(mode) {
    SkASSERT(kSrcIn_Mode == mode || kDstIn_Mode == mode || kSrcOver_Mode == mode);
}

SkLumaMaskXfermode::SkLumaMaskXfermode(SkFlattenableReadBuffer& buffer)
    : INHERITED(buffer)
    , fMode((SkXfermode::Mode)buffer.readUInt()) {
    SkASSERT(kSrcIn_Mode == fMode || kDstIn_Mode == fMode || kSrcOver_Mode == fMode);
}

void SkLumaMaskXfermode::flatten(SkFlattenableWriteBuffer& buffer) const {
    INHERITED::flatten(buffer);
    buffer.writeUInt(fMode);
}

SkPMColor SkLumaMaskXfermode::xferColor(SkPMColor src, SkPMColor dst) const {
    const SkPMColor* a = lumaOpA<SkPMColor>(fMode, &src, &dst);
    const SkPMColor* b = lumaOpB<SkPMColor>(fMode, &src, &dst);
    return this->lumaProc(*a, *b);
}

void SkLumaMaskXfermode::xfer32(SkPMColor dst[], const SkPMColor src[],
                                int count, const SkAlpha aa[]) const {
    const SkPMColor* a = lumaOpA<SkPMColor>(fMode, src, dst);
    const SkPMColor* b = lumaOpB<SkPMColor>(fMode, src, dst);

    if (aa) {
        for (int i = 0; i < count; ++i) {
            unsigned cov = aa[i];
            if (cov) {
                unsigned resC = this->lumaProc(a[i], b[i]);
                if (cov < 255) {
                    resC = SkFastFourByteInterp256(resC, dst[i],
                                                   SkAlpha255To256(cov));
                }
                dst[i] = resC;
            }
        }
    } else {
        for (int i = 0; i < count; ++i) {
            dst[i] = this->lumaProc(a[i], b[i]);
        }
    }
}

#ifdef SK_DEVELOPER
void SkLumaMaskXfermode::toString(SkString* str) const {
    str->printf("SkLumaMaskXfermode: mode: %s",
                fMode == kSrcIn_Mode ? "SRC_IN" :
                fMode == kDstIn_Mode ? "DST_IN" : "SRC_OVER");
}
#endif

SkLumaMaskXfermodeSrcOver::SkLumaMaskXfermodeSrcOver() : SkLumaMaskXfermode(kSrcOver_Mode) {}

SkLumaMaskXfermodeSrcOver::SkLumaMaskXfermodeSrcOver(SkFlattenableReadBuffer& buffer)
    : INHERITED(buffer) {
}

SkPMColor SkLumaMaskXfermodeSrcOver::lumaProc(const SkPMColor a, const SkPMColor b) const {
    unsigned luma = SkComputeLuminance(SkGetPackedR32(b),
                                       SkGetPackedG32(b),
                                       SkGetPackedB32(b));

    unsigned oldAlpha = SkGetPackedA32(b);
    unsigned newR = 0, newG = 0, newB = 0;

    if (oldAlpha > 0) {
        newR = SkGetPackedR32(b) * 255 / oldAlpha;
        newG = SkGetPackedG32(b) * 255 / oldAlpha;
        newB = SkGetPackedB32(b) * 255 / oldAlpha;
    }

    SkPMColor colorB = SkPremultiplyARGBInline(luma, newR, newG, newB);

    return SkPMSrcOver(colorB, a);
}

SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_START(SkLumaMaskXfermode)
    SK_DEFINE_FLATTENABLE_REGISTRAR_ENTRY(SkLumaMaskXfermode)
    SK_DEFINE_FLATTENABLE_REGISTRAR_ENTRY(SkLumaMaskXfermodeSrcOver)
SK_DEFINE_FLATTENABLE_REGISTRAR_GROUP_END

#if SK_SUPPORT_GPU
//////////////////////////////////////////////////////////////////////////////

class GrGLLumaMaskEffect : public GrGLEffect {
public:
    GrGLLumaMaskEffect(const GrBackendEffectFactory&, const GrDrawEffect&);
    virtual ~GrGLLumaMaskEffect();

    virtual void emitCode(GrGLShaderBuilder*,
                          const GrDrawEffect&,
                          EffectKey,
                          const char* outputColor,
                          const char* inputColor,
                          const TransformedCoordsArray&,
                          const TextureSamplerArray&) SK_OVERRIDE;

    static inline EffectKey GenKey(const GrDrawEffect&, const GrGLCaps&);

private:
    typedef GrGLEffect INHERITED;
};

class GrLumaMaskEffect : public GrEffect {
public:
    static GrEffectRef* Create(SkXfermode::Mode mode) {
        AutoEffectUnref effect(SkNEW_ARGS(GrLumaMaskEffect, (mode)));
        return CreateEffectRef(effect);
    }

    virtual ~GrLumaMaskEffect();

    typedef GrGLLumaMaskEffect GLEffect;
    static const char* Name() { return "LumaMask"; }

    virtual const GrBackendEffectFactory& getFactory() const SK_OVERRIDE;
    virtual void getConstantColorComponents(GrColor*, uint32_t*) const SK_OVERRIDE;

    SkXfermode::Mode getMode() const { return fMode; }

private:
    GrLumaMaskEffect(SkXfermode::Mode);

    virtual bool onIsEqual(const GrEffect&) const SK_OVERRIDE;

    const SkXfermode::Mode fMode;
};

//////////////////////////////////////////////////////////////////////////////

GrGLLumaMaskEffect::GrGLLumaMaskEffect(const GrBackendEffectFactory& factory,
                                       const GrDrawEffect&)
   : INHERITED(factory) {
}

GrGLLumaMaskEffect::~GrGLLumaMaskEffect() {
}

void GrGLLumaMaskEffect::emitCode(GrGLShaderBuilder* builder,
                                  const GrDrawEffect& effect,
                                  EffectKey key,
                                  const char* outputColor,
                                  const char* inputColor,
                                  const TransformedCoordsArray&,
                                  const TextureSamplerArray& samplers) {

    const GrLumaMaskEffect& lumaEffect = effect.castEffect<GrLumaMaskEffect>();
    const char* dstColor = builder->dstColor();
    SkASSERT(NULL != dstColor);
    if (NULL == inputColor) {
        inputColor = GrGLSLOnesVecf(4);
    }

    const char *opA = lumaOpA<char>(lumaEffect.getMode(), inputColor, dstColor);
    const char *opB = lumaOpB<char>(lumaEffect.getMode(), inputColor, dstColor);

    builder->fsCodeAppendf("\t\tfloat luma = dot(vec3(%f, %f, %f), %s.rgb); \n",
                           SK_ITU_BT709_LUM_COEFF_R,
                           SK_ITU_BT709_LUM_COEFF_G,
                           SK_ITU_BT709_LUM_COEFF_B,
                           opB);
    if (SkXfermode::kSrcOver_Mode == lumaEffect.getMode()) {
        builder->fsCodeAppendf("\t\tvec4 newB = %s;\n\t\tif (newB.a > 0.0) { newB *= luma / newB.a; }\n\t\tnewB.a = luma;\n", opB);
        builder->fsCodeAppendf("\t\t%s = newB + %s * (1.0 - luma); \n", outputColor, opA);
    } else {
        builder->fsCodeAppendf("\t\t%s = %s * luma;\n", outputColor, opA);
    }
}

GrGLEffect::EffectKey GrGLLumaMaskEffect::GenKey(const GrDrawEffect& drawEffect,
                                                 const GrGLCaps&) {
    const GrLumaMaskEffect& effect = drawEffect.castEffect<GrLumaMaskEffect>();
    return (EffectKey)effect.getMode();
}

//////////////////////////////////////////////////////////////////////////////

GrLumaMaskEffect::GrLumaMaskEffect(SkXfermode::Mode mode)
    : fMode(mode) {
    this->setWillReadDstColor();
}

GrLumaMaskEffect::~GrLumaMaskEffect() {
}

const GrBackendEffectFactory& GrLumaMaskEffect::getFactory() const {
    return GrTBackendEffectFactory<GrLumaMaskEffect>::getInstance();
}

void GrLumaMaskEffect::getConstantColorComponents(GrColor*, uint32_t *validFlags) const {
    *validFlags = 0;
}

bool GrLumaMaskEffect::onIsEqual(const GrEffect& sBase) const {
    return fMode == CastEffect<GrLumaMaskEffect>(sBase).fMode;
}

//////////////////////////////////////////////////////////////////////////////

bool SkLumaMaskXfermode::asNewEffectOrCoeff(GrContext*, GrEffectRef** effect,
                                            Coeff*, Coeff*,
                                            GrTexture* background) const {
    // No background texture support.
    if (effect && !background) {
        *effect = GrLumaMaskEffect::Create(fMode);
        return true;
    }

    return false;
}

#endif // SK_SUPPORT_GPU