Android NDK: From Elementary to Expert Episode 22

According to the comment of the code, ImageBlurring Project is making a comprise between gaussian blurring and box blur. And by further study in the project, I find out another method to blurring the bitmap. It can blur the format of RGB_565:

for (x = 0; x < w; x++) {

    r[yi] = dv[rsum];
    g[yi] = dv[gsum];
    b[yi] = dv[bsum];

    rsum -= routsum;
    gsum -= goutsum;
    bsum -= boutsum;

    stackstart = stackpointer - radius + div;
    sir = stack[stackstart % div];

    routsum -= sir[0];
    goutsum -= sir[1];
    boutsum -= sir[2];

    if (y == 0) {
        vmin[x] = MIN(x + radius + 1, wm);
    }
    p = pix[yw + vmin[x]];

    sir[0] = (((p) & 0xF800) >> 11) << 3;
    sir[1] = (((p) & 0x7E0) >> 5) << 2;
    sir[2] = ((p) & 0x1F) << 3;

    rinsum += sir[0];
    ginsum += sir[1];
    binsum += sir[2];

    rsum += rinsum;
    gsum += ginsum;
    bsum += binsum;

    stackpointer = (stackpointer + 1) % div;
    sir = stack[(stackpointer) % div];

    routsum += sir[0];
    goutsum += sir[1];
    boutsum += sir[2];

    rinsum -= sir[0];
    ginsum -= sir[1];
    binsum -= sir[2];

    yi++;
}

The key code of this algorithm is

sir[0] = (((p) & 0xF800) >> 11) << 3;
sir[1] = (((p) & 0x7E0) >> 5) << 2;
sir[2] = ((p) & 0x1F) << 3;

RenderScript also provide some APIs for the blurring features:

RenderScript rs = RenderScript.create(getActivity());
Allocation overlayAlloc = Allocation.createFromBitmap(rs, bitmap);
ScriptIntrinsicBlur blur = ScriptIntrinsicBlur.create(rs, overlayAlloc.getElement());
blur.setInput(overlayAlloc);
blur.setRadius(radius);
blur.forEach(overlayAlloc);
overlayAlloc.copyTo(bitmap);
rs.destroy();

Next article, I will study for RenderScript and NDK.