SkShader.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 SkShader_DEFINED
#define SkShader_DEFINED

#include "SkBitmap.h"
#include "SkFlattenable.h"
#include "SkImageInfo.h"
#include "SkMask.h"
#include "SkMatrix.h"
#include "SkPaint.h"
#include "../gpu/GrColor.h"

class SkColorFilter;
class SkColorSpace;
class SkImage;
class SkPath;
class SkPicture;
class SkXfermode;
class GrContext;
class GrFragmentProcessor;

class SK_API SkShader : public SkFlattenable {
public:
    SkShader(const SkMatrix* localMatrix = NULL);
    virtual ~SkShader();

    const SkMatrix& getLocalMatrix() const { return fLocalMatrix; }

    enum TileMode {
        kClamp_TileMode,

        kRepeat_TileMode,

        kMirror_TileMode,

#if 0

        kDecal_TileMode,
#endif
    };

    enum {
        kTileModeCount = kMirror_TileMode + 1
    };

    // override these in your subclass

    enum Flags {
        kOpaqueAlpha_Flag = 1 << 0,

        kConstInY32_Flag = 1 << 1,

        kPrefers4f_Flag  = 1 << 2,
    };

    virtual bool isOpaque() const { return false; }

    struct ContextRec {
        enum DstType {
            kPMColor_DstType, // clients prefer shading into PMColor dest
            kPM4f_DstType,    // clients prefer shading into PM4f dest
        };

        ContextRec(const SkPaint& paint, const SkMatrix& matrix, const SkMatrix* localM,
                   DstType dstType)
            : fPaint(&paint)
            , fMatrix(&matrix)
            , fLocalMatrix(localM)
            , fPreferredDstType(dstType) {}

        const SkPaint*  fPaint;            // the current paint associated with the draw
        const SkMatrix* fMatrix;           // the current matrix in the canvas
        const SkMatrix* fLocalMatrix;      // optional local matrix
        const DstType   fPreferredDstType; // the "natural" client dest type
    };

    class Context : public ::SkNoncopyable {
    public:
        Context(const SkShader& shader, const ContextRec&);

        virtual ~Context();

        virtual uint32_t getFlags() const { return 0; }

        virtual void shadeSpan(int x, int y, SkPMColor[], int count) = 0;

        virtual void shadeSpan4f(int x, int y, SkPM4f[], int count);

        struct BlitState;
        typedef void (*BlitBW)(BlitState*,
                               int x, int y, const SkPixmap&, int count);
        typedef void (*BlitAA)(BlitState*,
                               int x, int y, const SkPixmap&, int count, const SkAlpha[]);

        struct BlitState {
            // inputs
            Context*    fCtx;
            SkXfermode* fXfer;

            // outputs
            enum { N = 2 };
            void*       fStorage[N];
            BlitBW      fBlitBW;
            BlitAA      fBlitAA;
        };

        // Returns true if one or more of the blitprocs are set in the BlitState
        bool chooseBlitProcs(const SkImageInfo& info, BlitState* state) {
            state->fBlitBW = nullptr;
            state->fBlitAA = nullptr;
            if (this->onChooseBlitProcs(info, state)) {
                SkASSERT(state->fBlitBW || state->fBlitAA);
                return true;
            }
            return false;
        }

        typedef void (*ShadeProc)(const void* ctx, int x, int y, SkPMColor[], int count);
        virtual ShadeProc asAShadeProc(void** ctx);

        virtual void shadeSpanAlpha(int x, int y, uint8_t alpha[], int count);

        // Notification from blitter::blitMask in case we need to see the non-alpha channels
        virtual void set3DMask(const SkMask*) {}

    protected:
        // Reference to shader, so we don't have to dupe information.
        const SkShader& fShader;

        enum MatrixClass {
            kLinear_MatrixClass,            // no perspective
            kFixedStepInX_MatrixClass,      // fast perspective, need to call fixedStepInX() each
                                            // scanline
            kPerspective_MatrixClass        // slow perspective, need to mappoints each pixel
        };
        static MatrixClass ComputeMatrixClass(const SkMatrix&);

        uint8_t         getPaintAlpha() const { return fPaintAlpha; }
        const SkMatrix& getTotalInverse() const { return fTotalInverse; }
        MatrixClass     getInverseClass() const { return (MatrixClass)fTotalInverseClass; }
        const SkMatrix& getCTM() const { return fCTM; }

        virtual bool onChooseBlitProcs(const SkImageInfo&, BlitState*) { return false; }

    private:
        SkMatrix    fCTM;
        SkMatrix    fTotalInverse;
        uint8_t     fPaintAlpha;
        uint8_t     fTotalInverseClass;

        typedef SkNoncopyable INHERITED;
    };

    Context* createContext(const ContextRec&, void* storage) const;

    size_t contextSize(const ContextRec&) const;

    bool isABitmap(SkBitmap* outTexture, SkMatrix* outMatrix, TileMode xy[2]) const {
        return this->onIsABitmap(outTexture, outMatrix, xy);
    }

    bool isABitmap() const {
        return this->isABitmap(nullptr, nullptr, nullptr);
    }

    SkImage* isAImage(SkMatrix* localMatrix, TileMode xy[2]) const {
        return this->onIsAImage(localMatrix, xy);
    }

    bool isAImage() const {
        return this->isAImage(nullptr, nullptr) != nullptr;
    }

    enum GradientType {
        kNone_GradientType,
        kColor_GradientType,
        kLinear_GradientType,
        kRadial_GradientType,
        kSweep_GradientType,
        kConical_GradientType,
        kLast_GradientType = kConical_GradientType
    };

    struct GradientInfo {
        int         fColorCount;    
                                    //   of fColors/fColorOffsets on input, and
                                    //   actual number of colors/offsets on
                                    //   output.
        SkColor*    fColors;        
        SkScalar*   fColorOffsets;  
        SkPoint     fPoint[2];      
        SkScalar    fRadius[2];     
        TileMode    fTileMode;      
        uint32_t    fGradientFlags; 
    };

    virtual GradientType asAGradient(GradientInfo* info) const;

    struct ComposeRec {
        const SkShader*     fShaderA;
        const SkShader*     fShaderB;
        const SkXfermode*   fMode;
    };

    virtual bool asACompose(ComposeRec*) const { return false; }

#if SK_SUPPORT_GPU
    struct AsFPArgs {
        AsFPArgs(GrContext* context,
                 const SkMatrix* viewMatrix,
                 const SkMatrix* localMatrix,
                 SkFilterQuality filterQuality,
                 SkColorSpace* dstColorSpace,
                 SkSourceGammaTreatment gammaTreatment)
            : fContext(context)
            , fViewMatrix(viewMatrix)
            , fLocalMatrix(localMatrix)
            , fFilterQuality(filterQuality)
            , fDstColorSpace(dstColorSpace)
            , fGammaTreatment(gammaTreatment) {}

        GrContext*             fContext;
        const SkMatrix*        fViewMatrix;
        const SkMatrix*        fLocalMatrix;
        SkFilterQuality        fFilterQuality;
        SkColorSpace*          fDstColorSpace;
        SkSourceGammaTreatment fGammaTreatment;
    };

    virtual sk_sp<GrFragmentProcessor> asFragmentProcessor(const AsFPArgs&) const;
#endif

    bool asLuminanceColor(SkColor*) const;

#ifdef SK_BUILD_FOR_ANDROID_FRAMEWORK

    virtual bool asACustomShader(void** /* customData */) const { return false; }
#endif

    //  Methods to create combinations or variants of shaders

    sk_sp<SkShader> makeWithLocalMatrix(const SkMatrix&) const;

    sk_sp<SkShader> makeWithColorFilter(sk_sp<SkColorFilter>) const;

    //  Factory methods for stock shaders
    
    static sk_sp<SkShader> MakeEmptyShader();

    static sk_sp<SkShader> MakeColorShader(SkColor);

    static sk_sp<SkShader> MakeColorShader(const SkColor4f&, sk_sp<SkColorSpace>);

    static sk_sp<SkShader> MakeComposeShader(sk_sp<SkShader> dst, sk_sp<SkShader> src,
                                             SkXfermode::Mode);

#ifdef SK_SUPPORT_LEGACY_CREATESHADER_PTR
    static SkShader* CreateEmptyShader() { return MakeEmptyShader().release(); }
    static SkShader* CreateColorShader(SkColor c) { return MakeColorShader(c).release(); }
    static SkShader* CreateBitmapShader(const SkBitmap& src, TileMode tmx, TileMode tmy,
                                        const SkMatrix* localMatrix = nullptr) {
        return MakeBitmapShader(src, tmx, tmy, localMatrix).release();
    }
    static SkShader* CreateComposeShader(SkShader* dst, SkShader* src, SkXfermode::Mode mode);
    static SkShader* CreateComposeShader(SkShader* dst, SkShader* src, SkXfermode* xfer);
    static SkShader* CreatePictureShader(const SkPicture* src, TileMode tmx, TileMode tmy,
                                         const SkMatrix* localMatrix, const SkRect* tile);

    SkShader* newWithLocalMatrix(const SkMatrix& matrix) const {
        return this->makeWithLocalMatrix(matrix).release();
    }
    SkShader* newWithColorFilter(SkColorFilter* filter) const;
#endif

    static sk_sp<SkShader> MakeComposeShader(sk_sp<SkShader> dst, sk_sp<SkShader> src,
                                             sk_sp<SkXfermode> xfer);
#ifdef SK_SUPPORT_LEGACY_XFERMODE_PTR
    static sk_sp<SkShader> MakeComposeShader(sk_sp<SkShader> dst, sk_sp<SkShader> src,
                                             SkXfermode* xfer);
#endif

    static sk_sp<SkShader> MakeBitmapShader(const SkBitmap& src, TileMode tmx, TileMode tmy,
                                            const SkMatrix* localMatrix = nullptr);

    // NOTE: You can create an SkImage Shader with SkImage::newShader().

    static sk_sp<SkShader> MakePictureShader(sk_sp<SkPicture> src, TileMode tmx, TileMode tmy,
                                             const SkMatrix* localMatrix, const SkRect* tile);

    virtual SkShader* refAsALocalMatrixShader(SkMatrix* localMatrix) const;

    SK_TO_STRING_VIRT()
    SK_DEFINE_FLATTENABLE_TYPE(SkShader)
    SK_DECLARE_FLATTENABLE_REGISTRAR_GROUP()

protected:
    void flatten(SkWriteBuffer&) const override;

    bool computeTotalInverse(const ContextRec&, SkMatrix* totalInverse) const;

    virtual Context* onCreateContext(const ContextRec&, void* storage) const;

    virtual size_t onContextSize(const ContextRec&) const;

    virtual bool onAsLuminanceColor(SkColor*) const {
        return false;
    }

    virtual bool onIsABitmap(SkBitmap*, SkMatrix*, TileMode[2]) const {
        return false;
    }

    virtual SkImage* onIsAImage(SkMatrix*, TileMode[2]) const {
        return nullptr;
    }

private:
    // This is essentially const, but not officially so it can be modified in
    // constructors.
    SkMatrix fLocalMatrix;

    // So the SkLocalMatrixShader can whack fLocalMatrix in its SkReadBuffer constructor.
    friend class SkLocalMatrixShader;
    friend class SkBitmapProcLegacyShader;    // for computeTotalInverse()

    typedef SkFlattenable INHERITED;
};

#endif