include/graphics/SkPorterDuff.h

/* include/graphics/SkPorterDuff.h
**
** Copyright 2006, Google Inc.
**
** Licensed under the Apache License, Version 2.0 (the "License"); 
** you may not use this file except in compliance with the License. 
** You may obtain a copy of the License at 
**
**     http://www.apache.org/licenses/LICENSE-2.0 
**
** Unless required by applicable law or agreed to in writing, software 
** distributed under the License is distributed on an "AS IS" BASIS, 
** WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 
** See the License for the specific language governing permissions and 
** limitations under the License.
*/

#ifndef SkPorterDuff_DEFINED
#define SkPorterDuff_DEFINED

#include "SkColor.h"

class SkXfermode;

class SkPorterDuff {
public:
    /** List of predefined xfermodes. In general, the algebra for the modes
        uses the following symbols:
        Sa, Sc  - source alpha and color
        Da, Dc - destination alpha and color (before compositing)
        [a, c] - Resulting (alpha, color) values
        For these equations, the colors are in premultiplied state.
        If no xfermode is specified, kSrcOver is assumed.
    */
    enum Mode {
        kClear_Mode,    //!< [0, 0]
        kSrc_Mode,      //!< [Sa, Sc]
        kDst_Mode,      //!< [Da, Dc]
        kSrcOver_Mode,  //!< [Sa + (1 - Sa)*Da, Rc = Sc + (1 - Sa)*Dc] this is the default mode
        kDstOver_Mode,  //!< [Sa + (1 - Sa)*Da, Rc = Dc + (1 - Da)*Sc]
        kSrcIn_Mode,    //!< [Sa * Da, Sc * Da]
        kDstIn_Mode,    //!< [Sa * Da, Sa * Dc]
        kSrcOut_Mode,   //!< [Sa * (1 - Da), Sc * (1 - Da)]
        kDstOut_Mode,   //!< [Da * (1 - Sa), Dc * (1 - Sa)]
        kSrcATop_Mode,  //!< [Da, Sc * Da + (1 - Sa) * Dc]
        kDstATop_Mode,  //!< [Sa, Sa * Dc + Sc * (1 - Da)]
        kXor_Mode,      //!< [Sa + Da - 2 * Sa * Da, Sc * (1 - Da) + (1 - Sa) * Dc]
        kDarken_Mode,   //!< [Sa + Da - Sa\u00B7Da, Sc\u00B7(1 - Da) + Dc\u00B7(1 - Sa) + min(Sc, Dc)]
        kLighten_Mode,  //!< [Sa + Da - Sa\u00B7Da, Sc\u00B7(1 - Da) + Dc\u00B7(1 - Sa) + max(Sc, Dc)]

        kModeCount
    };
    /** Return an SkXfermode object for the specified mode.
    */
    static SkXfermode* CreateXfermode(Mode mode);
    
    /** Return a function pointer to a routine that applies the specified porter-duff
        transfer mode.
    */
    static SkXfermodeProc GetXfermodeProc(Mode mode);
};

#endif