Method cropBitmap

third-part/skia/src/images/SkImageDecoder.cpp:191–236

}

bool SkImageDecoder::cropBitmap(SkBitmap *dst, SkBitmap *src, int sampleSize,
                                int dstX, int dstY, int width, int height,
                                int srcX, int srcY) {
    int w = width / sampleSize;
    int h = height / sampleSize;
    if (src->colorType() == kIndex_8_SkColorType) {
        // kIndex8 does not allow drawing via an SkCanvas, as is done below.
        // Instead, use extractSubset. Note that this shares the SkPixelRef and
        // SkColorTable.
        // FIXME: Since src is discarded in practice, this holds on to more
        // pixels than is strictly necessary. Switch to a copy if memory
        // savings are more important than speed here. This also means
        // that the pixels in dst can not be reused (though there is no
        // allocation, which was already done on src).
        int x = (dstX - srcX) / sampleSize;
        int y = (dstY - srcY) / sampleSize;
        SkIRect subset = SkIRect::MakeXYWH(x, y, w, h);
        return src->extractSubset(dst, subset);
    }
    // if the destination has no pixels then we must allocate them.
    if (dst->isNull()) {
        dst->setInfo(src->info().makeWH(w, h));

        if (!this->allocPixelRef(dst, NULL)) {
            SkDEBUGF(("failed to allocate pixels needed to crop the bitmap"));
            return false;
        }
    }
    // check to see if the destination is large enough to decode the desired
    // region. If this assert fails we will just draw as much of the source
    // into the destination that we can.
    if (dst->width() < w || dst->height() < h) {
        SkDEBUGF(("SkImageDecoder::cropBitmap does not have a large enough bitmap.\n"));
    }

    // Set the Src_Mode for the paint to prevent transparency issue in the
    // dest in the event that the dest was being re-used.
    SkPaint paint;
    paint.setXfermodeMode(SkXfermode::kSrc_Mode);

    SkCanvas canvas(*dst);
    canvas.drawSprite(*src, (srcX - dstX) / sampleSize,
                            (srcY - dstY) / sampleSize,
                            &paint);
    return true;
}

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