src/core/SkBlitter.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 SkBlitter_DEFINED
#define SkBlitter_DEFINED

#include "SkBitmapProcShader.h"
#include "SkColor.h"
#include "SkRect.h"
#include "SkRegion.h"
#include "SkShader.h"
#include "SkTypes.h"

class SkMatrix;
class SkPaint;
class SkPixmap;
struct SkMask;

/** SkBlitter and its subclasses are responsible for actually writing pixels
    into memory. Besides efficiency, they handle clipping and antialiasing.
*/
class SkBlitter {
public:
    virtual ~SkBlitter();

    /// Blit a horizontal run of one or more pixels.
    virtual void blitH(int x, int y, int width);
    /// Blit a horizontal run of antialiased pixels; runs[] is a *sparse*
    /// zero-terminated run-length encoding of spans of constant alpha values.
    virtual void blitAntiH(int x, int y, const SkAlpha antialias[],
                           const int16_t runs[]);

    /// Blit a vertical run of pixels with a constant alpha value.
    virtual void blitV(int x, int y, int height, SkAlpha alpha);
    /// Blit a solid rectangle one or more pixels wide.
    virtual void blitRect(int x, int y, int width, int height);
    /** Blit a rectangle with one alpha-blended column on the left,
        width (zero or more) opaque pixels, and one alpha-blended column
        on the right.
        The result will always be at least two pixels wide.
    */
    virtual void blitAntiRect(int x, int y, int width, int height,
                              SkAlpha leftAlpha, SkAlpha rightAlpha);
    /// Blit a pattern of pixels defined by a rectangle-clipped mask;
    /// typically used for text.
    virtual void blitMask(const SkMask&, const SkIRect& clip);

    /** If the blitter just sets a single value for each pixel, return the
        bitmap it draws into, and assign value. If not, return NULL and ignore
        the value parameter.
    */
    virtual const SkPixmap* justAnOpaqueColor(uint32_t* value);

    // (x, y), (x + 1, y)
    virtual void blitAntiH2(int x, int y, U8CPU a0, U8CPU a1) {
        int16_t runs[3];
        uint8_t aa[2];
        
        runs[0] = 1;
        runs[1] = 1;
        runs[2] = 0;
        aa[0] = SkToU8(a0);
        aa[1] = SkToU8(a1);
        this->blitAntiH(x, y, aa, runs);
    }

    // (x, y), (x, y + 1)
    virtual void blitAntiV2(int x, int y, U8CPU a0, U8CPU a1) {
        int16_t runs[2];
        uint8_t aa[1];
        
        runs[0] = 1;
        runs[1] = 0;
        aa[0] = SkToU8(a0);
        this->blitAntiH(x, y, aa, runs);
        // reset in case the clipping blitter modified runs
        runs[0] = 1;
        runs[1] = 0;
        aa[0] = SkToU8(a1);
        this->blitAntiH(x, y + 1, aa, runs);
    }
    
    /**
     *  Special method just to identify the null blitter, which is returned
     *  from Choose() if the request cannot be fulfilled. Default impl
     *  returns false.
     */
    virtual bool isNullBlitter() const;

    /**
     *  Special methods for SkShaderBlitter. On all other classes this is a no-op.
     */
    virtual bool resetShaderContext(const SkShader::ContextRec&);
    virtual SkShader::Context* getShaderContext() const;

    /**
     * Special methods for blitters that can blit more than one row at a time.
     * This function returns the number of rows that this blitter could optimally
     * process at a time. It is still required to support blitting one scanline
     * at a time.
     */
    virtual int requestRowsPreserved() const { return 1; }

    /**
     * This function allocates memory for the blitter that the blitter then owns.
     * The memory can be used by the calling function at will, but it will be
     * released when the blitter's destructor is called. This function returns
     * NULL if no persistent memory is needed by the blitter.
     */
    virtual void* allocBlitMemory(size_t sz) {
        return fBlitMemory.reset(sz, SkAutoMalloc::kReuse_OnShrink);
    }

    ///@name non-virtual helpers
    void blitMaskRegion(const SkMask& mask, const SkRegion& clip);
    void blitRectRegion(const SkIRect& rect, const SkRegion& clip);
    void blitRegion(const SkRegion& clip);
    ///@}

    /** @name Factories
        Return the correct blitter to use given the specified context.
     */
    static SkBlitter* Choose(const SkPixmap& dst,
                             const SkMatrix& matrix,
                             const SkPaint& paint,
                             SkTBlitterAllocator*,
                             bool drawCoverage = false);

    static SkBlitter* ChooseSprite(const SkPixmap& dst,
                                   const SkPaint&,
                                   const SkPixmap& src,
                                   int left, int top,
                                   SkTBlitterAllocator*);
    ///@}

protected:
    SkAutoMalloc fBlitMemory;
};

/** This blitter silently never draws anything.
*/
class SkNullBlitter : public SkBlitter {
public:
    void blitH(int x, int y, int width) override;
    void blitAntiH(int x, int y, const SkAlpha[], const int16_t runs[]) override;
    void blitV(int x, int y, int height, SkAlpha alpha) override;
    void blitRect(int x, int y, int width, int height) override;
    void blitMask(const SkMask&, const SkIRect& clip) override;
    const SkPixmap* justAnOpaqueColor(uint32_t* value) override;
    bool isNullBlitter() const override;
};

/** Wraps another (real) blitter, and ensures that the real blitter is only
    called with coordinates that have been clipped by the specified clipRect.
    This means the caller need not perform the clipping ahead of time.
*/
class SkRectClipBlitter : public SkBlitter {
public:
    void init(SkBlitter* blitter, const SkIRect& clipRect) {
        SkASSERT(!clipRect.isEmpty());
        fBlitter = blitter;
        fClipRect = clipRect;
    }

    void blitH(int x, int y, int width) override;
    void blitAntiH(int x, int y, const SkAlpha[], const int16_t runs[]) override;
    void blitV(int x, int y, int height, SkAlpha alpha) override;
    void blitRect(int x, int y, int width, int height) override;
    virtual void blitAntiRect(int x, int y, int width, int height,
                     SkAlpha leftAlpha, SkAlpha rightAlpha) override;
    void blitMask(const SkMask&, const SkIRect& clip) override;
    const SkPixmap* justAnOpaqueColor(uint32_t* value) override;

    int requestRowsPreserved() const override {
        return fBlitter->requestRowsPreserved();
    }

    void* allocBlitMemory(size_t sz) override {
        return fBlitter->allocBlitMemory(sz);
    }

private:
    SkBlitter*  fBlitter;
    SkIRect     fClipRect;
};

/** Wraps another (real) blitter, and ensures that the real blitter is only
    called with coordinates that have been clipped by the specified clipRgn.
    This means the caller need not perform the clipping ahead of time.
*/
class SkRgnClipBlitter : public SkBlitter {
public:
    void init(SkBlitter* blitter, const SkRegion* clipRgn) {
        SkASSERT(clipRgn && !clipRgn->isEmpty());
        fBlitter = blitter;
        fRgn = clipRgn;
    }

    void blitH(int x, int y, int width) override;
    void blitAntiH(int x, int y, const SkAlpha[], const int16_t runs[]) override;
    void blitV(int x, int y, int height, SkAlpha alpha) override;
    void blitRect(int x, int y, int width, int height) override;
    void blitAntiRect(int x, int y, int width, int height,
                      SkAlpha leftAlpha, SkAlpha rightAlpha) override;
    void blitMask(const SkMask&, const SkIRect& clip) override;
    const SkPixmap* justAnOpaqueColor(uint32_t* value) override;

    int requestRowsPreserved() const override {
        return fBlitter->requestRowsPreserved();
    }

    void* allocBlitMemory(size_t sz) override {
        return fBlitter->allocBlitMemory(sz);
    }

private:
    SkBlitter*      fBlitter;
    const SkRegion* fRgn;
};

/** Factory to set up the appropriate most-efficient wrapper blitter
    to apply a clip. Returns a pointer to a member, so lifetime must
    be managed carefully.
*/
class SkBlitterClipper {
public:
    SkBlitter*  apply(SkBlitter* blitter, const SkRegion* clip,
                      const SkIRect* bounds = NULL);

private:
    SkNullBlitter       fNullBlitter;
    SkRectClipBlitter   fRectBlitter;
    SkRgnClipBlitter    fRgnBlitter;
};

#endif