src/gpu/effects/GrConfigConversionEffect.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 GrConfigConversionEffect_DEFINED
#define GrConfigConversionEffect_DEFINED

#include "GrSingleTextureEffect.h"

class GrGLConfigConversionEffect;

/**
 * This class is used to perform config conversions. Clients may want to read/write data that is
 * unpremultiplied. Also on some systems reading/writing BGRA or RGBA is faster. In those cases we
 * read/write using the faster path and perform an R/B swap in the shader if the client data is in
 * the slower config.
 */
class GrConfigConversionEffect : public GrSingleTextureEffect {
public:
    /**
     * The PM->UPM or UPM->PM conversions to apply.
     */
    enum PMConversion {
        kNone_PMConversion = 0,
        kMulByAlpha_RoundUp_PMConversion,
        kMulByAlpha_RoundDown_PMConversion,
        kDivByAlpha_RoundUp_PMConversion,
        kDivByAlpha_RoundDown_PMConversion,

        kPMConversionCnt
    };

    // This will fail if the config is not 8888 and a PM conversion is requested.
    static GrCustomStage* Create(GrTexture*,
                                 bool swapRedAndBlue,
                                 PMConversion pmConversion = kNone_PMConversion);

    static const char* Name() { return "Config Conversion"; }
    typedef GrGLConfigConversionEffect GLProgramStage;

    virtual const GrProgramStageFactory& getFactory() const SK_OVERRIDE;
    virtual bool isEqual(const GrCustomStage&) const SK_OVERRIDE;

    bool swapsRedAndBlue() const { return fSwapRedAndBlue; }
    PMConversion  pmConversion() const { return fPMConversion; }

    // This function determines whether it is possible to choose PM->UPM and UPM->PM conversions
    // for which in any PM->UPM->PM->UPM sequence the two UPM values are the same. This means that
    // if pixels are read back to a UPM buffer, written back to PM to the GPU, and read back again
    // both reads will produce the same result. This test is quite expensive and should not be run
    // multiple times for a given context.
    static void TestForPreservingPMConversions(GrContext* context,
                                               PMConversion* PMToUPMRule,
                                               PMConversion* UPMToPMRule);

private:
    GrConfigConversionEffect(GrTexture*,
                            bool swapRedAndBlue,
                            PMConversion pmConversion);

    bool            fSwapRedAndBlue;
    PMConversion    fPMConversion;

    GR_DECLARE_CUSTOM_STAGE_TEST;

    typedef GrSingleTextureEffect INHERITED;
};

#endif