Clipping - Computer Graphics and Geometric Modeling - page 74

begin { Clip against bottom bdry }
x := x0 + (x1 - x0)*(ymin - y0)/(y1 - y0);
y := ymin;

end
else if (TOPBDRY and c) π 0
then
begin { Clip against top bdry }
x := x0 + (x1 - x0)*(ymax - y0)/(y1 - y0);
y := ymax;
end ;

{ Next update the clipped endpoint and its code }
if c = c0
then
begin
x0 := x; y0 := y;
c0 := RegionCode (x0,y0);

end

else

begin
x1 := x; y1 := y;
c1 := RegionCode (x1,y1);

end
end ; { while }

return ( true );
end ;

byte function RegionCode ( real x,y);
{ Return the 4-bit code for the point (x,y) }
begin
byte c;

c := 0;
if x < xmin
then c := c + LEFTBDRY
else if x > xmax
then c := c + RIGHTBDRY;

if y < ymin
then c := c + BOTTOMBDRY
else if y > ymax
then c := c + TOPBDRY;
return (c);
end ;

{ RegionCode }

Algorithm 3.2.1.1. Continued