public void makeOneStep() {
        // Do the work
        xPosition += xDelta;
        if (xPosition < 0 || xPosition >= xLimit) {
            xPosition = (xPosition < 0)? xPosition + xLimit: xPosition -xLimit;
        }
        yPosition += yDelta;
        if (yPosition < 0 || yPosition >= yLimit) {
            yPosition = (yPosition < 0)? yPosition + xLimit: yPosition -xLimit;
        }
    }