program julia_col; {creates a Julia set in colour. This is almost exactly the
               same as the 'mset' program, except for some essential
               alterations in the mathematics. See the sections "The
               Mandelbort Set" and "The Julia Sets" for more detail.}

uses crt, graph;

var     xcorner, y2corner, x2corner, ycorner: real;
        xsize, ysize, k, i, xgap, ygap, max: integer;
        ca, cb, za2, za1, za, zb: real;
        gd, gm: integer;
        count: word;



procedure iterate;
begin
count := 0;
za2 := za;
while 1=1 do
begin
za1 := za2;
za2 := (za1 * za1 - zb * zb) + ca;
zb := za1 * zb * 2 + cb;
IF za2 * za2 + zb * zb > 4 THEN EXIT;
count := count + 1;
IF count > max THEN EXIT
end;
END;



procedure main;
begin
gd := Detect;
InitGraph(gd, gm, 'd:\tp\bgi');
xcorner := -1.5;
y2corner := 1.5;
x2corner := 1.5;
ycorner := -1.5;
max := 50;
xsize := 400;
ysize := 400;
xgap := 10;
ygap := 10;
{CLS}
FOR k := ysize downTO 1 do
FOR i := 1 TO xsize do
begin
za := (i / xsize) * (x2corner - xcorner) + xcorner;
zb := (k / ysize) * (y2corner - ycorner) + ycorner;
ca := 0.360284; {Enter the co-ords for the Julia set here.}
cb := 0.100376;
iterate;
if count > max then count := 0;
setcolor(count);
LINE (xgap + i, ygap +ysize- k, xgap+i, ygap +ysize- k)
end;
end;



begin
main;
end.