public void drawViewfinder() {
        Bitmap resultBitmap = this.resultBitmap;
        this.resultBitmap = null;
        if (resultBitmap != null) {
            resultBitmap.recycle();
        }
        invalidate();
    }
This view is overlaid on top of the camera preview. It adds the viewfinder rectangle and partial
transparency outside it, as well as the laser scanner animation and result points.

@author dswitkin@google.com (Daniel Switkin)
zxing-android-embedded/src/com/journeyapps/barcodescanner/ViewfinderView.java