Properly set the center of the circular mask.

        }

        double cx = (maskWidth - 1.0) / 2.0;

        double cy = (maskHeight - 1.0) / 2.0;

        double cy = (maskHeight - 1.0 + mScreenOffset) / 2.0;

        double radius = maskWidth / 2.0;

        int[] pixels = new int[maskWidth * maskHeight];