1. A method of clipping a polygon against a window in a two-dimensional plane in which imaginary boundary lines correspond to window borders, extensions of the imaginary boundary lines divide the two-dimensional plane into regions, sides of the boundary lines on which the window lie are defined as the visible sides, and the other sides of the boundary lines are defined as the invisible sides, said method comprising the steps of: a. dividing vertices of the polygon into groups of consecutive vertices with respect to the window; b. identifying each group as a visible group or an invisible group; and c. processing the groups of consecutive vertices together, said visible groups being processed by comparing each vertex with the window borders and clipping the edge of the polygon between consecutive vertices of adjacent groups using a line clipping algorithm, and said invisible groups being processed by initially determining the location of the first vertices in the invisible group and designating that region as the designated invisible side (DIS), comparing the next vertex with the DIS to determine if that vertex is in the DIS and continuing until a vertex is found which is not in the DIS, and clipping the edge of the polygon between consecutive vertices which are in the DIS and not in the DIS respectively to determine whether there are intersection points between the edge and the window boundary.