public void setMarginFraction(double marginFraction) {
        if (marginFraction >= 0.5d) {
            throw new IllegalArgumentException("The margin fraction must be less than 0.5");
        }
        this.marginFraction = marginFraction;
    }
The the fraction of the width/height of view to be used as a margin for the framing rect.
This is ignored if framingRectSize is specified.

@param marginFraction the fraction
zxing-android-embedded/src/com/journeyapps/barcodescanner/CameraPreview.java