And here is the fantastic algorithm behind the DLA fractal :)

[code]DIM screen|(320,200)
DIM precalc&(4000,1)
th=90
' Fill array screen with initial values
FOR i=0 TO 179 STEP 0.5
 x1=160+COSQ(th+i)*10
 y1=100+SINQ(th+i)*10
 x2=160-COSQ(th+i)*10
 y2=y1
 FOR j=x1 TO x2
   screen|(j,y1)=1
 NEXT j
NEXT i
counter=1
screen_address%=XBIOS(2)
' Load image
DIM buffer|(32066-1)
buf_address%=V:buffer|(0)
BLOAD "stot8.pi1",buf_address%
~XBIOS(6,L:buf_address%+2)
RC_COPY buf_address%+34,0,0,320,200 TO screen_address%,0,0
feed
fractal
saving
PROCEDURE feed
 ' place a particle in a random position on  the periphery of a circle
 ' of radius r
 fi=RAND(360)
 r=15+INT((counter/3.14)^0.63)
 x=INT(160+r*COSQ(fi))
 y=INT(100+r*SINQ(fi))
 IF screen|(x,y)=1 THEN
   GOSUB feed
 ENDIF
 IF screen|(x-1,y-1)=1 OR screen|(x-1,y)=1 OR screen|(x-1,y+1)=1 OR screen|(x,y-1)=1 OR screen|(x,y+1)=1 OR screen|(x+1,y-1)=1 OR screen|(x+1,y)=1 OR screen|(x+1,y+1)=1 THEN
   screen|(x,y)=1
   GOSUB feed
 ENDIF
RETURN
PROCEDURE fractal
 ' This is the DLA algorithm. Particle follows brownian motion. In each step
 ' a check is being performed for the existance of a neigbouring particle.
 ' If such a particle exists then the particle sticks and a new one is being
 ' released
 DO
   REM  theta=RAND(360)
   n%=RANDOM(3)-1
   x=x+n%
   IF x<160-r THEN
     x=165-r
   ENDIF
   IF x>160+r THEN
     x=155+r
   ENDIF
   IF screen|(x,y)=1 THEN
     GOSUB fractal
   ENDIF
   IF screen|(x-1,y-1)=1 OR screen|(x-1,y)=1 OR screen|(x-1,y+1)=1 OR screen|(x,y-1)=1 OR screen|(x,y+1)=1 OR screen|(x+1,y-1)=1 OR screen|(x+1,y)=1 OR screen|(x+1,y+1)=1 THEN
     screen|(x,y)=1
     PLOT x,y
     insert=1
     IF insert=1 THEN
       counter=counter+1
       precalc&(counter,0)=x
       precalc&(counter,1)=y
       GOSUB feed
     ENDIF
   ENDIF
   REM theta=RAND(360)
   m%=RANDOM(3)-1
   y=y+m%
   IF y<100-r THEN
     y=105-r
   ENDIF
   IF y>100+r THEN
     y=95+r
   ENDIF
   IF screen|(x-1,y-1)=1 OR screen|(x-1,y)=1 OR screen|(x-1,y+1)=1 OR screen|(x,y-1)=1 OR screen|(x,y+1)=1 OR screen|(x+1,y-1)=1 OR screen|(x+1,y)=1 OR screen|(x+1,y+1)=1 THEN
     screen|(x,y)=1
     PLOT x,y
     insert=1
     IF insert=1 THEN
       counter=counter+1
       precalc&(counter,0)=x
       precalc&(counter,1)=y
     ENDIF
   ENDIF
   ' PRINT AT(1,1);x,y,counter,r
   COLOR y/10
   IF counter>3500
     GOSUB saving
   ENDIF
 LOOP
RETURN
PROCEDURE saving
 BSAVE "precalc.chr",V:precalc&(0,0),4000*2*2
 END
RETURN
[/code]