Android bitmap erase(透過)

graphics/java/android/graphics/Bitmap.java
public void eraseColor(int c)
↓
graphics/java/android/graphics/Bitmap.java
nativeErase(mNativeBitmap, c)
↓
android/platform_frameworks_base/core/jni/android/graphics/Bitmap.cpp
nativeErase=>Bitmap_erase =>bitmap->eraseColor(color)
↓

android/platform_external_skia/include/core/SkBitmap.h
eraseColor()
void eraseColor(SkColor c) const {
this->eraseARGB(SkColorGetA(c), SkColorGetR(c), SkColorGetG(c),
SkColorGetB(c));
}

android/platform_external_skia/src/core/SkBitmap.cpp

void SkBitmap::eraseARGB(U8CPU a, U8CPU r, U8CPU g, U8CPU b) const {
    SkDEBUGCODE(this->validate();)

    if (0 == fWidth || 0 == fHeight ||
            kNo_Config == fConfig || kIndex8_Config == fConfig) {
        return;
    }

    SkAutoLockPixels alp(*this);
    // perform this check after the lock call
    if (!this->readyToDraw()) {
        return;
    }

    int height = fHeight;
    const int width = fWidth;
    const int rowBytes = fRowBytes;

    // make rgb premultiplied
    if (255 != a) {
        r = SkAlphaMul(r, a);
        g = SkAlphaMul(g, a);
        b = SkAlphaMul(b, a);
    }

    switch (fConfig) {
　　　　　（略）
        case kARGB_8888_Config: {
            uint32_t* p = (uint32_t*)fPixels;
            uint32_t v = SkPackARGB32(a, r, g, b);

            while (--height >= 0) {
                sk_memset32(p, v, width);
                p = (uint32_t*)((char*)p + rowBytes);
            }
            break;
        }
    }

    this->notifyPixelsChanged();
}

android/platform_external_skia/src/core/SkCanvas.cpp

void SkCanvas::drawBitmap(const SkBitmap& bitmap, SkScalar x, SkScalar y,
                          const SkPaint* paint) {
    SkDEBUGCODE(bitmap.validate();)

    if (NULL == paint || (paint->getMaskFilter() == NULL)) {
        SkRect fastBounds;
        fastBounds.set(x, y,
                       x + SkIntToScalar(bitmap.width()),
                       y + SkIntToScalar(bitmap.height()));
        if (this->quickReject(fastBounds, paint2EdgeType(paint))) {
            return;
        }
    }

    SkMatrix matrix;
    matrix.setTranslate(x, y);
    this->internalDrawBitmap(bitmap, NULL, matrix, paint);
}

void SkCanvas::internalDrawBitmap(const SkBitmap& bitmap, const SkIRect* srcRect,
                                const SkMatrix& matrix, const SkPaint* paint) {
    if (reject_bitmap(bitmap)) {
        return;
    }

    SkLazyPaint lazy;
    if (NULL == paint) {
        paint = lazy.init();
    }
    this->commonDrawBitmap(bitmap, srcRect, matrix, *paint);
}

void SkCanvas::commonDrawBitmap(const SkBitmap& bitmap, const SkIRect* srcRect,
                                const SkMatrix& matrix, const SkPaint& paint) {
    SkDEBUGCODE(bitmap.validate();)

    LOOPER_BEGIN(paint, SkDrawFilter::kBitmap_Type)

    while (iter.next()) {
        iter.fDevice->drawBitmap(iter, bitmap, srcRect, matrix, looper.paint());
    }

    LOOPER_END
}

android/platform_external_skia/src/core/SkDevice.cpp

void SkDevice::drawBitmap(const SkDraw& draw, const SkBitmap& bitmap,
                          const SkIRect* srcRect,
                          const SkMatrix& matrix, const SkPaint& paint) {
    SkBitmap tmp; // storage if we need a subset of bitmap
    const SkBitmap* bitmapPtr = &bitmap;

    if (srcRect) {
        if (!bitmap.extractSubset(&tmp, *srcRect)) {
            return; // extraction failed
        }
        bitmapPtr = &tmp;
    }
    draw.drawBitmap(*bitmapPtr, matrix, paint);
}

android/platform_external_skia/src/core/SkDraw.cpp

void SkDraw::drawBitmap(const SkBitmap& bitmap, const SkMatrix& prematrix,
                        const SkPaint& paint) const {
    SkDEBUGCODE(this->validate();)

    // nothing to draw
    if (fClip->isEmpty() ||
            bitmap.width() == 0 || bitmap.height() == 0 ||
            bitmap.getConfig() == SkBitmap::kNo_Config ||
            (paint.getAlpha() == 0 && paint.getXfermode() == NULL)) {
        return;
    }

#ifndef SK_ALLOW_OVER_32K_BITMAPS
    // run away on too-big bitmaps for now (exceed 16.16)
    if (bitmap.width() > 32767 || bitmap.height() > 32767) {
        return;
    }
#endif

    SkAutoPaintStyleRestore restore(paint, SkPaint::kFill_Style);

    SkMatrix matrix;
    if (!matrix.setConcat(*fMatrix, prematrix)) {
        return;
    }

    if (clipped_out(matrix, *fClip, bitmap.width(), bitmap.height())) {
        return;
    }

    if (fBounder && just_translate(matrix, bitmap)) {
        SkIRect ir;
        int32_t ix = SkScalarRound(matrix.getTranslateX());
        int32_t iy = SkScalarRound(matrix.getTranslateY());
        ir.set(ix, iy, ix + bitmap.width(), iy + bitmap.height());
        if (!fBounder->doIRect(ir)) {
            return;
        }
    }

    // only lock the pixels if we passed the clip and bounder tests
    SkAutoLockPixels alp(bitmap);
    // after the lock, check if we are valid
    if (!bitmap.readyToDraw()) {
        return;
    }

    if (bitmap.getConfig() != SkBitmap::kA8_Config &&
            just_translate(matrix, bitmap)) {
        int ix = SkScalarRound(matrix.getTranslateX());
        int iy = SkScalarRound(matrix.getTranslateY());
        uint32_t storage[kBlitterStorageLongCount];
        SkBlitter* blitter = SkBlitter::ChooseSprite(*fBitmap, paint, bitmap,
                                            ix, iy, storage, sizeof(storage));
        if (blitter) {
            SkAutoTPlacementDelete<SkBlitter> ad(blitter, storage);

            SkIRect ir;
            ir.set(ix, iy, ix + bitmap.width(), iy + bitmap.height());

            SkRegion::Cliperator iter(*fClip, ir);
            const SkIRect& cr = iter.rect();

            for (; !iter.done(); iter.next()) {
                SkASSERT(!cr.isEmpty());
                blitter->blitRect(cr.fLeft, cr.fTop, cr.width(), cr.height());
            }
            return;
        }
#if 0
SkDebugf("---- MISSING sprite case: config=%d [%d %d], device=%d, xfer=%p, alpha=0x%X colorFilter=%p\n",
bitmap.config(), bitmap.width(), bitmap.height(), fBitmap->config(),
paint.getXfermode(), paint.getAlpha(), paint.getColorFilter());
#endif
    }

    // now make a temp draw on the stack, and use it
    //
    SkDraw draw(*this);
    draw.fMatrix = &matrix;

    if (bitmap.getConfig() == SkBitmap::kA8_Config) {
        draw.drawBitmapAsMask(bitmap, paint);
    } else {
        SkAutoBitmapShaderInstall install(bitmap, &paint);

        SkRect r;
        r.set(0, 0, SkIntToScalar(bitmap.width()),
              SkIntToScalar(bitmap.height()));
        // is this ok if paint has a rasterizer?
        draw.drawRect(r, paint);
    }
}