src/core/SkBlitter.cpp

/* libs/graphics/sgl/SkBlitter.cpp
**
** Copyright 2006, The Android Open Source Project
**
** 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.
*/

#include "SkBlitter.h"
#include "SkAntiRun.h"
#include "SkColor.h"
#include "SkColorFilter.h"
#include "SkMask.h"
#include "SkMaskFilter.h"
#include "SkTemplatesPriv.h"
#include "SkUtils.h"
#include "SkXfermode.h"

SkBlitter::~SkBlitter() {}

const SkBitmap* SkBlitter::justAnOpaqueColor(uint32_t* value)
{
    return NULL;
}

void SkBlitter::blitH(int x, int y, int width)
{
    SkASSERT(!"unimplemented");
}

void SkBlitter::blitAntiH(int x, int y, const SkAlpha antialias[], const int16_t runs[])
{
    SkASSERT(!"unimplemented");
}

void SkBlitter::blitV(int x, int y, int height, SkAlpha alpha)
{
    if (alpha == 255)
        this->blitRect(x, y, 1, height);
    else
    {
        int16_t runs[2];
        runs[0] = 1;
        runs[1] = 0;

        while (--height >= 0)
            this->blitAntiH(x, y++, &alpha, runs);
    }
}

void SkBlitter::blitRect(int x, int y, int width, int height)
{
    while (--height >= 0)
        this->blitH(x, y++, width);
}

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

static inline void bits_to_runs(SkBlitter* blitter, int x, int y, const uint8_t bits[],
                                U8CPU left_mask, int rowBytes, U8CPU right_mask)
{
    int inFill = 0;
    int pos = 0;

    while (--rowBytes >= 0)
    {
        unsigned b = *bits++ & left_mask;
        if (rowBytes == 0)
            b &= right_mask;

        for (unsigned test = 0x80; test != 0; test >>= 1)
        {
            if (b & test)
            {
                if (!inFill)
                {
                    pos = x;
                    inFill = true;
                }
            }
            else
            {
                if (inFill)
                {
                    blitter->blitH(pos, y, x - pos);
                    inFill = false;
                }
            }
            x += 1;
        }
        left_mask = 0xFF;
    }

    // final cleanup
    if (inFill)
        blitter->blitH(pos, y, x - pos);
}

void SkBlitter::blitMask(const SkMask& mask, const SkIRect& clip)
{
    SkASSERT(mask.fBounds.contains(clip));

    if (mask.fFormat == SkMask::kBW_Format)
    {
        int cx = clip.fLeft;
        int cy = clip.fTop;
        int maskLeft = mask.fBounds.fLeft;
        int mask_rowBytes = mask.fRowBytes;
        int height = clip.height();

        const uint8_t* bits = mask.getAddr1(cx, cy);

        if (cx == maskLeft && clip.fRight == mask.fBounds.fRight)
        {
            while (--height >= 0)
            {
                bits_to_runs(this, cx, cy, bits, 0xFF, mask_rowBytes, 0xFF);
                bits += mask_rowBytes;
                cy += 1;
            }
        }
        else
        {
            int left_edge = cx - maskLeft;
            SkASSERT(left_edge >= 0);
            int rite_edge = clip.fRight - maskLeft;
            SkASSERT(rite_edge > left_edge);

            int left_mask = 0xFF >> (left_edge & 7);
            int rite_mask = 0xFF << (8 - (rite_edge & 7));
            int full_runs = (rite_edge >> 3) - ((left_edge + 7) >> 3);

            // check for empty right mask, so we don't read off the end (or go slower than we need to)
            if (rite_mask == 0)
            {
                SkASSERT(full_runs >= 0);
                full_runs -= 1;
                rite_mask = 0xFF;
            }
            if (left_mask == 0xFF)
                full_runs -= 1;

            // back up manually so we can keep in sync with our byte-aligned src
            // have cx reflect our actual starting x-coord
            cx -= left_edge & 7;

            if (full_runs < 0)
            {
                SkASSERT((left_mask & rite_mask) != 0);
                while (--height >= 0)
                {
                    bits_to_runs(this, cx, cy, bits, left_mask, 1, rite_mask);
                    bits += mask_rowBytes;
                    cy += 1;
                }
            }
            else
            {
                while (--height >= 0)
                {
                    bits_to_runs(this, cx, cy, bits, left_mask, full_runs + 2, rite_mask);
                    bits += mask_rowBytes;
                    cy += 1;
                }
            }
        }
    }
    else
    {
        int                         width = clip.width();
        SkAutoSTMalloc<64, int16_t> runStorage(width + 1);
        int16_t*                    runs = runStorage.get();
        const uint8_t*              aa = mask.getAddr(clip.fLeft, clip.fTop);

        sk_memset16((uint16_t*)runs, 1, width);
        runs[width] = 0;

        int height = clip.height();
        int y = clip.fTop;
        while (--height >= 0)
        {
            this->blitAntiH(clip.fLeft, y, aa, runs);
            aa += mask.fRowBytes;
            y += 1;
        }
    }
}

/////////////////////// these guys are not virtual, just a helpers

void SkBlitter::blitMaskRegion(const SkMask& mask, const SkRegion& clip) {
    if (clip.quickReject(mask.fBounds)) {
        return;
    }
    
    SkRegion::Cliperator clipper(clip, mask.fBounds);
    
    while (!clipper.done()) {
        const SkIRect& cr = clipper.rect();
        this->blitMask(mask, cr);
        clipper.next();
    }
}

void SkBlitter::blitRectRegion(const SkIRect& rect, const SkRegion& clip) {
    SkRegion::Cliperator clipper(clip, rect);
    
    while (!clipper.done()) {
        const SkIRect& cr = clipper.rect();
        this->blitRect(cr.fLeft, cr.fTop, cr.width(), cr.height());
        clipper.next();
    }
}

void SkBlitter::blitRegion(const SkRegion& clip) {
    SkRegion::Iterator iter(clip);
    
    while (!iter.done()) {
        const SkIRect& cr = iter.rect();
        this->blitRect(cr.fLeft, cr.fTop, cr.width(), cr.height());
        iter.next();
    }
}

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

void SkNullBlitter::blitH(int x, int y, int width)
{
}

void SkNullBlitter::blitAntiH(int x, int y, const SkAlpha antialias[], const int16_t runs[])
{
}

void SkNullBlitter::blitV(int x, int y, int height, SkAlpha alpha)
{
}

void SkNullBlitter::blitRect(int x, int y, int width, int height)
{
}

void SkNullBlitter::blitMask(const SkMask& mask, const SkIRect& clip)
{
}

const SkBitmap* SkNullBlitter::justAnOpaqueColor(uint32_t* value)
{
    return NULL;
}

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

static int compute_anti_width(const int16_t runs[])
{
    int width = 0;
    
    for (;;)
    {
        int count = runs[0];
        
        SkASSERT(count >= 0);
        if (count == 0)
            break;
        width += count;
        runs += count;
        
        SkASSERT(width < 20000);
    }
    return width;
}

static inline bool y_in_rect(int y, const SkIRect& rect)
{
    return (unsigned)(y - rect.fTop) < (unsigned)rect.height();
}

static inline bool x_in_rect(int x, const SkIRect& rect)
{
    return (unsigned)(x - rect.fLeft) < (unsigned)rect.width();
}

void SkRectClipBlitter::blitH(int left, int y, int width)
{
    SkASSERT(width > 0);

    if (!y_in_rect(y, fClipRect))
        return;

    int right = left + width;

    if (left < fClipRect.fLeft)
        left = fClipRect.fLeft;
    if (right > fClipRect.fRight)
        right = fClipRect.fRight;

    width = right - left;
    if (width > 0)
        fBlitter->blitH(left, y, width);
}

void SkRectClipBlitter::blitAntiH(int left, int y, const SkAlpha aa[], const int16_t runs[])
{
    if (!y_in_rect(y, fClipRect) || left >= fClipRect.fRight)
        return;

    int x0 = left;
    int x1 = left + compute_anti_width(runs);

    if (x1 <= fClipRect.fLeft)
        return;

    SkASSERT(x0 < x1);
    if (x0 < fClipRect.fLeft)
    {
        int dx = fClipRect.fLeft - x0;
        SkAlphaRuns::BreakAt((int16_t*)runs, (uint8_t*)aa, dx);
        runs += dx;
        aa += dx;
        x0 = fClipRect.fLeft;
    }

    SkASSERT(x0 < x1 && runs[x1 - x0] == 0);
    if (x1 > fClipRect.fRight)
    {
        x1 = fClipRect.fRight;
        SkAlphaRuns::BreakAt((int16_t*)runs, (uint8_t*)aa, x1 - x0);
        ((int16_t*)runs)[x1 - x0] = 0;
    }

    SkASSERT(x0 < x1 && runs[x1 - x0] == 0);
    SkASSERT(compute_anti_width(runs) == x1 - x0);

    fBlitter->blitAntiH(x0, y, aa, runs);
}

void SkRectClipBlitter::blitV(int x, int y, int height, SkAlpha alpha)
{
    SkASSERT(height > 0);

    if (!x_in_rect(x, fClipRect))
        return;

    int y0 = y;
    int y1 = y + height;

    if (y0 < fClipRect.fTop)
        y0 = fClipRect.fTop;
    if (y1 > fClipRect.fBottom)
        y1 = fClipRect.fBottom;

    if (y0 < y1)
        fBlitter->blitV(x, y0, y1 - y0, alpha);
}

void SkRectClipBlitter::blitRect(int left, int y, int width, int height)
{
    SkIRect    r;

    r.set(left, y, left + width, y + height);
    if (r.intersect(fClipRect))
        fBlitter->blitRect(r.fLeft, r.fTop, r.width(), r.height());
}

void SkRectClipBlitter::blitMask(const SkMask& mask, const SkIRect& clip)
{
    SkASSERT(mask.fBounds.contains(clip));

    SkIRect    r = clip;

    if (r.intersect(fClipRect))
        fBlitter->blitMask(mask, r);
}

const SkBitmap* SkRectClipBlitter::justAnOpaqueColor(uint32_t* value)
{
    return fBlitter->justAnOpaqueColor(value);
}

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

void SkRgnClipBlitter::blitH(int x, int y, int width)
{
    SkRegion::Spanerator span(*fRgn, y, x, x + width);
    int left, right;

    while (span.next(&left, &right))
    {
        SkASSERT(left < right);
        fBlitter->blitH(left, y, right - left);
    }
}

void SkRgnClipBlitter::blitAntiH(int x, int y, const SkAlpha aa[], const int16_t runs[])
{
    int width = compute_anti_width(runs);
    SkRegion::Spanerator span(*fRgn, y, x, x + width);
    int left, right;
    SkDEBUGCODE(const SkIRect& bounds = fRgn->getBounds();)
        
    int prevRite = x;
    while (span.next(&left, &right))
    {
        SkASSERT(x <= left);
        SkASSERT(left < right);
        SkASSERT(left >= bounds.fLeft && right <= bounds.fRight);
        
        SkAlphaRuns::Break((int16_t*)runs, (uint8_t*)aa, left - x, right - left);

        // now zero before left
        if (left > prevRite)
        {
            int index = prevRite - x;
            ((uint8_t*)aa)[index] = 0;   // skip runs after right
            ((int16_t*)runs)[index] = SkToS16(left - prevRite);
        }
        
        prevRite = right;
    }
    
    if (prevRite > x)
    {
        ((int16_t*)runs)[prevRite - x] = 0;
        
        if (x < 0) {
            int skip = runs[0];
            SkASSERT(skip >= -x);
            aa += skip;
            runs += skip;
            x += skip;
        }
        fBlitter->blitAntiH(x, y, aa, runs);
    }
}

void SkRgnClipBlitter::blitV(int x, int y, int height, SkAlpha alpha)
{
    SkIRect    bounds;
    bounds.set(x, y, x + 1, y + height);

    SkRegion::Cliperator    iter(*fRgn, bounds);

    while (!iter.done())
    {
        const SkIRect& r = iter.rect();
        SkASSERT(bounds.contains(r));

        fBlitter->blitV(x, r.fTop, r.height(), alpha);
        iter.next();
    }
}

void SkRgnClipBlitter::blitRect(int x, int y, int width, int height)
{
    SkIRect    bounds;
    bounds.set(x, y, x + width, y + height);

    SkRegion::Cliperator    iter(*fRgn, bounds);

    while (!iter.done())
    {
        const SkIRect& r = iter.rect();
        SkASSERT(bounds.contains(r));

        fBlitter->blitRect(r.fLeft, r.fTop, r.width(), r.height());
        iter.next();
    }
}

void SkRgnClipBlitter::blitMask(const SkMask& mask, const SkIRect& clip)
{
    SkASSERT(mask.fBounds.contains(clip));

    SkRegion::Cliperator iter(*fRgn, clip);
    const SkIRect&       r = iter.rect();
    SkBlitter*           blitter = fBlitter;

    while (!iter.done())
    {
        blitter->blitMask(mask, r);
        iter.next();
    }
}

const SkBitmap* SkRgnClipBlitter::justAnOpaqueColor(uint32_t* value)
{
    return fBlitter->justAnOpaqueColor(value);
}

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

SkBlitter* SkBlitterClipper::apply(SkBlitter* blitter, const SkRegion* clip, const SkIRect* ir)
{
    if (clip)
    {
        const SkIRect& clipR = clip->getBounds();

        if (clip->isEmpty() || (ir && !SkIRect::Intersects(clipR, *ir)))
            blitter = &fNullBlitter;
        else if (clip->isRect())
        {
            if (ir == NULL || !clipR.contains(*ir))
            {
                fRectBlitter.init(blitter, clipR);
                blitter = &fRectBlitter;
            }
        }
        else
        {
            fRgnBlitter.init(blitter, clip);
            blitter = &fRgnBlitter;
        }
    }
    return blitter;
}

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

#include "SkColorShader.h"
#include "SkColorPriv.h"

class Sk3DShader : public SkShader {
public:
    Sk3DShader(SkShader* proxy) : fProxy(proxy)
    {
        proxy->safeRef();
        fMask = NULL;
    }
    virtual ~Sk3DShader()
    {
        fProxy->safeUnref();
    }
    void setMask(const SkMask* mask) { fMask = mask; }

    virtual bool setContext(const SkBitmap& device, const SkPaint& paint, const SkMatrix& matrix)
    {
        if (fProxy)
            return fProxy->setContext(device, paint, matrix);
        else
        {
            fPMColor = SkPreMultiplyColor(paint.getColor());
            return this->INHERITED::setContext(device, paint, matrix);
        }
    }
    virtual void shadeSpan(int x, int y, SkPMColor span[], int count)
    {
        if (fProxy)
            fProxy->shadeSpan(x, y, span, count);

        if (fMask == NULL)
        {
            if (fProxy == NULL)
                sk_memset32(span, fPMColor, count);
            return;
        }

        SkASSERT(fMask->fBounds.contains(x, y));
        SkASSERT(fMask->fBounds.contains(x + count - 1, y));

        size_t          size = fMask->computeImageSize();
        const uint8_t*  alpha = fMask->getAddr(x, y);
        const uint8_t*  mulp = alpha + size;
        const uint8_t*  addp = mulp + size;

        if (fProxy)
        {
            for (int i = 0; i < count; i++)
            {
                if (alpha[i])
                {
                    SkPMColor c = span[i];
                    if (c)
                    {
                        unsigned a = SkGetPackedA32(c);
                        unsigned r = SkGetPackedR32(c);
                        unsigned g = SkGetPackedG32(c);
                        unsigned b = SkGetPackedB32(c);

                        unsigned mul = SkAlpha255To256(mulp[i]);
                        unsigned add = addp[i];

                        r = SkFastMin32(SkAlphaMul(r, mul) + add, a);
                        g = SkFastMin32(SkAlphaMul(g, mul) + add, a);
                        b = SkFastMin32(SkAlphaMul(b, mul) + add, a);

                        span[i] = SkPackARGB32(a, r, g, b);
                    }
                }
                else
                    span[i] = 0;
            }
        }
        else    // color
        {
            unsigned a = SkGetPackedA32(fPMColor);
            unsigned r = SkGetPackedR32(fPMColor);
            unsigned g = SkGetPackedG32(fPMColor);
            unsigned b = SkGetPackedB32(fPMColor);
            for (int i = 0; i < count; i++)
            {
                if (alpha[i])
                {
                    unsigned mul = SkAlpha255To256(mulp[i]);
                    unsigned add = addp[i];

                    span[i] = SkPackARGB32( a,
                                            SkFastMin32(SkAlphaMul(r, mul) + add, a),
                                            SkFastMin32(SkAlphaMul(g, mul) + add, a),
                                            SkFastMin32(SkAlphaMul(b, mul) + add, a));
                }
                else
                    span[i] = 0;
            }
        }
    }
    
    virtual void beginSession()
    {
        this->INHERITED::beginSession();
        if (fProxy)
            fProxy->beginSession();
    }
    
    virtual void endSession()
    {
        if (fProxy)
            fProxy->endSession();
        this->INHERITED::endSession();
    }

protected:
    Sk3DShader(SkFlattenableReadBuffer& buffer) :
        INHERITED(buffer)
    {
        fProxy = static_cast<SkShader*>(buffer.readFlattenable());
        fPMColor = buffer.readU32();
        fMask = NULL;
    }
    
    virtual void flatten(SkFlattenableWriteBuffer& buffer) 
    {
        this->INHERITED::flatten(buffer);
        buffer.writeFlattenable(fProxy);
        buffer.write32(fPMColor);
    }
    
    virtual Factory getFactory() 
    { 
        return CreateProc;
    }

private:
    static SkFlattenable* CreateProc(SkFlattenableReadBuffer& buffer) 
    {
        return SkNEW_ARGS(Sk3DShader, (buffer));
    }

    SkShader*       fProxy;
    SkPMColor       fPMColor;
    const SkMask*   fMask;

    typedef SkShader INHERITED;
};

class Sk3DBlitter : public SkBlitter {
public:
    Sk3DBlitter(SkBlitter* proxy, Sk3DShader* shader, void (*killProc)(void*))
        : fProxy(proxy), f3DShader(shader), fKillProc(killProc)
    {
        shader->ref();
    }
    virtual ~Sk3DBlitter()
    {
        f3DShader->unref();
        fKillProc(fProxy);
    }

    virtual void blitH(int x, int y, int width)
    {
        fProxy->blitH(x, y, width);
    }
    virtual void blitAntiH(int x, int y, const SkAlpha antialias[], const int16_t runs[])
    {
        fProxy->blitAntiH(x, y, antialias, runs);
    }
    virtual void blitV(int x, int y, int height, SkAlpha alpha)
    {
        fProxy->blitV(x, y, height, alpha);
    }
    virtual void blitRect(int x, int y, int width, int height)
    {
        fProxy->blitRect(x, y, width, height);
    }
    virtual void blitMask(const SkMask& mask, const SkIRect& clip)
    {
        if (mask.fFormat == SkMask::k3D_Format)
        {
            f3DShader->setMask(&mask);

            ((SkMask*)&mask)->fFormat = SkMask::kA8_Format;
            fProxy->blitMask(mask, clip);
            ((SkMask*)&mask)->fFormat = SkMask::k3D_Format;

            f3DShader->setMask(NULL);
        }
        else
            fProxy->blitMask(mask, clip);
    }
private:
    SkBlitter*  fProxy;
    Sk3DShader* f3DShader;
    void        (*fKillProc)(void*);
};

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

#include "SkCoreBlitters.h"

class SkAutoRestoreShader {
public:
    SkAutoRestoreShader(const SkPaint& p) : fPaint((SkPaint*)&p)
    {
        fShader = fPaint->getShader();
        fShader->safeRef();
    }
    ~SkAutoRestoreShader()
    {
        fPaint->setShader(fShader);
        fShader->safeUnref();
    }
private:
    SkPaint*    fPaint;
    SkShader*   fShader;
};

class SkAutoCallProc {
public:
    typedef void (*Proc)(void*);
    SkAutoCallProc(void* obj, Proc proc)
        : fObj(obj), fProc(proc)
    {
    }
    ~SkAutoCallProc()
    {
        if (fObj && fProc)
            fProc(fObj);
    }
    void* get() const { return fObj; }
    void* detach()
    {
        void* obj = fObj;
        fObj = NULL;
        return obj;
    }
private:
    void*   fObj;
    Proc    fProc;
};

static void destroy_blitter(void* blitter)
{
    ((SkBlitter*)blitter)->~SkBlitter();
}

static void delete_blitter(void* blitter)
{
    SkDELETE((SkBlitter*)blitter);
}

static bool just_solid_color(const SkPaint& paint) {
    if (paint.getAlpha() == 0xFF && paint.getColorFilter() == NULL) {
        SkShader* shader = paint.getShader();
        if (NULL == shader ||
            (shader->getFlags() & SkShader::kOpaqueAlpha_Flag)) {
            return true;
        }
    }
    return false;
}
    
/** By analyzing the paint (with an xfermode), we may decide we can take
    special action. This enum lists our possible actions
 */
enum XferInterp {
    kNormal_XferInterp,         // no special interpretation, draw normally
    kSrcOver_XferInterp,        // draw as if in srcover mode
    kSkipDrawing_XferInterp     // draw nothing
};

static XferInterp interpret_xfermode(const SkPaint& paint, SkXfermode* xfer,
                                     SkBitmap::Config deviceConfig) {
    SkXfermode::Mode  mode;
    
    if (SkXfermode::IsMode(xfer, &mode)) {
        switch (mode) {
            case SkXfermode::kSrc_Mode:
                if (just_solid_color(paint)) {
                    return kSrcOver_XferInterp;
                }
                break;
            case SkXfermode::kDst_Mode:
                return kSkipDrawing_XferInterp;
            case SkXfermode::kSrcOver_Mode:
                return kSrcOver_XferInterp;
            case SkXfermode::kDstOver_Mode:
                if (SkBitmap::kRGB_565_Config == deviceConfig) {
                    return kSkipDrawing_XferInterp;
                }
                break;
            case SkXfermode::kSrcIn_Mode:
                if (SkBitmap::kRGB_565_Config == deviceConfig &&
                    just_solid_color(paint)) {
                    return kSrcOver_XferInterp;
                }
                break;
            case SkXfermode::kDstIn_Mode:
                if (just_solid_color(paint)) {
                    return kSkipDrawing_XferInterp;
                }
                break;
            default:
                break;
        }
    }
    return kNormal_XferInterp;
}

SkBlitter* SkBlitter::Choose(const SkBitmap& device,
                             const SkMatrix& matrix,
                             const SkPaint& paint,
                             void* storage, size_t storageSize)
{
    SkASSERT(storageSize == 0 || storage != NULL);

    SkBlitter*  blitter = NULL;

    // which check, in case we're being called by a client with a dummy device
    // (e.g. they have a bounder that always aborts the draw)
    if (SkBitmap::kNo_Config == device.getConfig())
    {
        SK_PLACEMENT_NEW(blitter, SkNullBlitter, storage, storageSize);
        return blitter;
    }

    SkAutoRestoreShader restore(paint);
    SkShader* shader = paint.getShader();

    Sk3DShader* shader3D = NULL;
    if (paint.getMaskFilter() != NULL && paint.getMaskFilter()->getFormat() == SkMask::k3D_Format)
    {
        shader3D = SkNEW_ARGS(Sk3DShader, (shader));
        ((SkPaint*)&paint)->setShader(shader3D)->unref();
        shader = shader3D;
    }

    SkXfermode* mode = paint.getXfermode();
    if (NULL != mode) {
        switch (interpret_xfermode(paint, mode, device.config())) {
            case kSrcOver_XferInterp:
                mode = NULL;
                break;
            case kSkipDrawing_XferInterp:
                SK_PLACEMENT_NEW(blitter, SkNullBlitter, storage, storageSize);
                return blitter;
            default:
                break;
        }
    }

    if (NULL == shader && (NULL != mode || paint.getColorFilter() != NULL))
    {
        // xfermodes require shaders for our current set of blitters
        shader = SkNEW(SkColorShader);
        ((SkPaint*)&paint)->setShader(shader)->unref();
    }
    
    if (paint.getColorFilter() != NULL)
    {
        SkASSERT(shader);
        shader = SkNEW_ARGS(SkFilterShader, (shader, paint.getColorFilter()));
        ((SkPaint*)&paint)->setShader(shader)->unref();
    }
    
    bool doDither = paint.isDither();

    if (shader)
    {
        if (!shader->setContext(device, paint, matrix))
            return SkNEW(SkNullBlitter);
        
        // disable dither if our shader is natively 16bit (no need to upsample)
        if (shader->getFlags() & SkShader::kIntrinsicly16_Flag)
            doDither = false;
    }

    switch (device.getConfig()) {
    case SkBitmap::kA1_Config:
        SK_PLACEMENT_NEW_ARGS(blitter, SkA1_Blitter, storage, storageSize, (device, paint));
        break;

    case SkBitmap::kA8_Config:
        if (shader)
            SK_PLACEMENT_NEW_ARGS(blitter, SkA8_Shader_Blitter, storage, storageSize, (device, paint));
        else
            SK_PLACEMENT_NEW_ARGS(blitter, SkA8_Blitter, storage, storageSize, (device, paint));
        break;
        
    case SkBitmap::kARGB_4444_Config:
        blitter = SkBlitter_ChooseD4444(device, paint, storage, storageSize);
        break;

    case SkBitmap::kRGB_565_Config:
        if (shader)
        {
            if (mode)
                SK_PLACEMENT_NEW_ARGS(blitter, SkRGB16_Shader_Xfermode_Blitter, storage, storageSize, (device, paint));
            else if (SkShader::CanCallShadeSpan16(shader->getFlags()) && !doDither)
                SK_PLACEMENT_NEW_ARGS(blitter, SkRGB16_Shader16_Blitter, storage, storageSize, (device, paint));
            else
                SK_PLACEMENT_NEW_ARGS(blitter, SkRGB16_Shader_Blitter, storage, storageSize, (device, paint));
        } else {
            SkColor color = paint.getColor();
            if (0 == SkColorGetA(color)) {
                SK_PLACEMENT_NEW(blitter, SkNullBlitter, storage, storageSize);
            } else if (SK_ColorBLACK == color) {
                SK_PLACEMENT_NEW_ARGS(blitter, SkRGB16_Black_Blitter, storage,
                                      storageSize, (device, paint));
            } else if (0xFF == SkColorGetA(color)) {
                SK_PLACEMENT_NEW_ARGS(blitter, SkRGB16_Opaque_Blitter, storage,
                                      storageSize, (device, paint));
            } else {
                SK_PLACEMENT_NEW_ARGS(blitter, SkRGB16_Blitter, storage,
                                      storageSize, (device, paint));
            }
        }
        break;

    case SkBitmap::kARGB_8888_Config:
        if (shader)
            SK_PLACEMENT_NEW_ARGS(blitter, SkARGB32_Shader_Blitter, storage, storageSize, (device, paint));
        else if (paint.getColor() == SK_ColorBLACK)
            SK_PLACEMENT_NEW_ARGS(blitter, SkARGB32_Black_Blitter, storage, storageSize, (device, paint));
        else if (paint.getAlpha() == 0xFF)
            SK_PLACEMENT_NEW_ARGS(blitter, SkARGB32_Opaque_Blitter, storage, storageSize, (device, paint));
        else
            SK_PLACEMENT_NEW_ARGS(blitter, SkARGB32_Blitter, storage, storageSize, (device, paint));
        break;

    default:
        SkASSERT(!"unsupported device config");
        SK_PLACEMENT_NEW(blitter, SkNullBlitter, storage, storageSize);
    }

    if (shader3D)
    {
        void (*proc)(void*) = ((void*)storage == (void*)blitter) ? destroy_blitter : delete_blitter;
        SkAutoCallProc  tmp(blitter, proc);

        blitter = SkNEW_ARGS(Sk3DBlitter, (blitter, shader3D, proc));
        (void)tmp.detach();
    }
    return blitter;
}

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

const uint16_t gMask_0F0F = 0xF0F;
const uint32_t gMask_00FF00FF = 0xFF00FF;

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

SkShaderBlitter::SkShaderBlitter(const SkBitmap& device, const SkPaint& paint)
        : INHERITED(device) {
    fShader = paint.getShader();
    SkASSERT(fShader);

    fShader->ref();
    fShader->beginSession();
    fShaderFlags = fShader->getFlags();
}

SkShaderBlitter::~SkShaderBlitter() {
    fShader->endSession();
    fShader->unref();
}