Visible Surface Algorithms - Computer Graphics and Geometric Modeling - page 281

procedure UpdateActiveEdgeList ()
begin
edgedata E;

for E in activeEdges do
if E.dy = 0
then Delete E from activeEdges
else

begin
E.dy := E.dy - 1;
E.x := E.x + E.dx;
end ;

end ;

Procedure UpdateActivePolygonList ()
begin
polydata P;

for P in activePolys do
if P.dy = 0 then Delete P from activePolys
else P.dy := P.dy - 1;

end ;

Algorithm 7.8.1. Continued

Figure 7.9. A Watkins scan line algorithm example.