``````{
From: SEAN PALMER
Subj: Bresenham's Line

You need a plot(x,y) procedure and a global color variable to use these as
posted. }

{bresenham's line}
procedure line(x,y,x2,y2:integer);var d,dx,dy,ai,bi,xi,yi:integer;begin
if(x<x2)then begin xi:=1;dx:=x2-x;end else begin xi:=-1;dx:=x-x2;end;
if(y<y2)then begin yi:=1;dy:=y2-y;end else begin yi:=-1;dy:=y-y2;end;
plot(x,y);
if dx>dy then begin ai:=(dy-dx)*2;bi:=dy*2; d:=bi-dx;
repeat
if(d>=0)then begin inc(y,yi);inc(d,ai);end else inc(d,bi);
inc(x,xi);plot(x,y);
until(x=x2);
end
else begin ai:=(dx-dy)*2;bi:=dx*2; d:=bi-dy;
repeat
if(d>=0)then begin inc(x,xi);inc(d,ai);end else inc(d,bi);
inc(y,yi);plot(x,y);
until(y=y2);
end;
end;

{filled ellipse}
procedure disk(xc,yc,a,b:integer);
var x,y:integer; aa,aa2,bb,bb2,d,dx,dy:longint; begin
x:=0;y:=b;
aa:=longint(a)*a; aa2:=2*aa;
bb:=longint(b)*b; bb2:=2*bb;
d:=bb-aa*b+aa div 4;
dx:=0;dy:=aa2*b;
vLin(xc,yc-y,yc+y);
while(dx<dy)do begin
if(d>0)then begin dec(y); dec(dy,aa2); dec(d,dy); end;
inc(x); inc(dx,bb2); inc(d,bb+dx);
vLin(xc-x,yc-y,yc+y);vLin(xc+x,yc-y,yc+y);
end;
inc(d,(3*(aa-bb)div 2-(dx+dy))div 2);
while(y>=0)do begin
if(d<0)then begin
inc(x); inc(dx,bb2); inc(d,bb+dx);
vLin(xc-x,yc-y,yc+y);vLin(xc+x,yc-y,yc+y);
end;
dec(y); dec(dy,aa2); inc(d,aa-dy);
end;
end;

``````