include/core/SkComposeShader.h

/*
 * Copyright 2006 The Android Open Source Project
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */


#ifndef SkComposeShader_DEFINED
#define SkComposeShader_DEFINED

#include "SkShader.h"

class SkXfermode;

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

/** \class SkComposeShader
    This subclass of shader returns the composition of two other shaders, combined by
    a xfermode.
*/
class SK_API SkComposeShader : public SkShader {
public:
    /** Create a new compose shader, given shaders A, B, and a combining xfermode mode.
        When the xfermode is called, it will be given the result from shader A as its
        "dst", and the result from shader B as its "src".
        mode->xfer32(sA_result, sB_result, ...)
        @param shaderA  The colors from this shader are seen as the "dst" by the xfermode
        @param shaderB  The colors from this shader are seen as the "src" by the xfermode
        @param mode     The xfermode that combines the colors from the two shaders. If mode
                        is null, then SRC_OVER is assumed.
    */
    SkComposeShader(SkShader* sA, SkShader* sB, SkXfermode* mode = NULL);
    virtual ~SkComposeShader();

    virtual bool validContext(const SkBitmap&, const SkPaint&,
                              const SkMatrix&, SkMatrix* totalInverse = NULL) const SK_OVERRIDE;
    virtual SkShader::Context* createContext(const SkBitmap&, const SkPaint&,
                                             const SkMatrix&, void*) const SK_OVERRIDE;
    virtual size_t contextSize() const SK_OVERRIDE;

    class ComposeShaderContext : public SkShader::Context {
    public:
        // When this object gets destroyed, it will call contextA and contextB's destructor
        // but it will NOT free the memory.
        ComposeShaderContext(const SkComposeShader&, const SkBitmap&,
                             const SkPaint&, const SkMatrix&,
                             SkShader::Context* contextA, SkShader::Context* contextB);

        SkShader::Context* getShaderContextA() const { return fShaderContextA; }
        SkShader::Context* getShaderContextB() const { return fShaderContextB; }

        virtual ~ComposeShaderContext();

        virtual void shadeSpan(int x, int y, SkPMColor[], int count) SK_OVERRIDE;

    private:
        SkShader::Context* fShaderContextA;
        SkShader::Context* fShaderContextB;

        typedef SkShader::Context INHERITED;
    };

#ifdef SK_DEBUG
    SkShader* getShaderA() { return fShaderA; }
    SkShader* getShaderB() { return fShaderB; }
#endif

    SK_TO_STRING_OVERRIDE()
    SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkComposeShader)

protected:
    SkComposeShader(SkReadBuffer& );
    virtual void flatten(SkWriteBuffer&) const SK_OVERRIDE;

private:
    SkShader*   fShaderA;
    SkShader*   fShaderB;
    SkXfermode* fMode;

    typedef SkShader INHERITED;
};

#endif