Clipping a point/line is quite easy in a way, in the case of an abscissa in a general shape also. First of all, we test its end points, and if they belong to the display box so also the whole abscissa lies inside the display box. If the abscissa lies outside, we test the abscissa's penetration through its display box. If the abscissa crosses the display box, we clip it, and for this it is necessary to find the conjunction points.