private static Tristrip gpc_strip_ToTristrip(gpc_tristrip gpc_strip)
        {
            Tristrip tristrip = new Tristrip();

            tristrip.NofStrips = gpc_strip.num_strips;
            tristrip.Strip     = new VertexList[tristrip.NofStrips];
            IntPtr ptr = gpc_strip.strip;

            for (int i = 0; i < tristrip.NofStrips; i++)
            {
                tristrip.Strip[i] = new VertexList();
                gpc_vertex_list gpc_vtx_list = (gpc_vertex_list)Marshal.PtrToStructure(ptr, typeof(gpc_vertex_list));
                tristrip.Strip[i].NofVertices = gpc_vtx_list.num_vertices;
                tristrip.Strip[i].Vertex      = new Vertex[tristrip.Strip[i].NofVertices];

                IntPtr ptr2 = gpc_vtx_list.vertex;
                for (int j = 0; j < tristrip.Strip[i].NofVertices; j++)
                {
                    gpc_vertex gpc_vtx = (gpc_vertex)Marshal.PtrToStructure(ptr2, typeof(gpc_vertex));
                    tristrip.Strip[i].Vertex[j].X = gpc_vtx.x;
                    tristrip.Strip[i].Vertex[j].Y = gpc_vtx.y;

                    ptr2 = (IntPtr)(((int)ptr2) + Marshal.SizeOf(gpc_vtx));
                }
                ptr = (IntPtr)(((int)ptr) + Marshal.SizeOf(gpc_vtx_list));
            }

            return(tristrip);
        }
        public static Tristrip PolygonToTristrip(Polygon polygon)
        {
            gpc_tristrip gpc_strip = new gpc_tristrip();
            gpc_polygon  gpc_pol   = GpcWrapper.PolygonTo_gpc_polygon(polygon);

            gpc_polygon_to_tristrip(ref gpc_pol, ref gpc_strip);
            Tristrip tristrip = GpcWrapper.gpc_strip_ToTristrip(gpc_strip);

            GpcWrapper.Free_gpc_polygon(gpc_pol);
            GpcWrapper.gpc_free_tristrip(ref gpc_strip);

            return(tristrip);
        }
        public static Tristrip ClipToTristrip(GpcOperation operation, Polygon subject_polygon, Polygon clip_polygon)
        {
            gpc_tristrip gpc_strip           = new gpc_tristrip();
            gpc_polygon  gpc_subject_polygon = GpcWrapper.PolygonTo_gpc_polygon(subject_polygon);
            gpc_polygon  gpc_clip_polygon    = GpcWrapper.PolygonTo_gpc_polygon(clip_polygon);

            gpc_tristrip_clip(operation, ref gpc_subject_polygon, ref gpc_clip_polygon, ref gpc_strip);
            Tristrip tristrip = GpcWrapper.gpc_strip_ToTristrip(gpc_strip);

            GpcWrapper.Free_gpc_polygon(gpc_subject_polygon);
            GpcWrapper.Free_gpc_polygon(gpc_clip_polygon);
            GpcWrapper.gpc_free_tristrip(ref gpc_strip);

            return(tristrip);
        }
        private static Tristrip gpc_strip_ToTristrip( gpc_tristrip gpc_strip )
        {
            Tristrip tristrip  = new Tristrip();
            tristrip.NofStrips = gpc_strip.num_strips;
            tristrip.Strip     = new VertexList[tristrip.NofStrips];
            IntPtr ptr = gpc_strip.strip;
            for ( int i=0 ; i<tristrip.NofStrips ; i++ ) {
                tristrip.Strip[i] = new VertexList();
                gpc_vertex_list gpc_vtx_list = (gpc_vertex_list)Marshal.PtrToStructure( ptr, typeof(gpc_vertex_list) );
                tristrip.Strip[i].NofVertices = gpc_vtx_list.num_vertices;
                tristrip.Strip[i].Vertex      = new Vertex[tristrip.Strip[i].NofVertices];

                IntPtr ptr2 = gpc_vtx_list.vertex;
                for ( int j=0 ; j<tristrip.Strip[i].NofVertices ; j++ ) {
                    gpc_vertex gpc_vtx = (gpc_vertex)Marshal.PtrToStructure( ptr2, typeof(gpc_vertex) );
                    tristrip.Strip[i].Vertex[j].X = gpc_vtx.x;
                    tristrip.Strip[i].Vertex[j].Y = gpc_vtx.y;

                    ptr2 = (IntPtr)( ((int)ptr2) + Marshal.SizeOf(gpc_vtx) );
                }
                ptr = (IntPtr)( ((int)ptr) + Marshal.SizeOf(gpc_vtx_list) );
            }

            return tristrip;
        }