Sutherland-Hodgman algorithm For a polygon consisting of P1, P2, ... Pn, in general it is correct. But still there are some subtle situations we need to handle. Take a look at the following picture. In the algorithm, we only calculate the intersections of the polygon edges and the viewport, i.e., the portions of line segments of edges that should be inside the viewport. However, we have not discussed which portion of the polygon that should be inside of the viewport.