DECLARE SUB Box(x1!,y1!,x2!,y2!)
CLEAR,,16384
RANDOMIZE TIMER
SCREEN 1
DIM SHARED Rf
Rf=2
PSET(0,0),1'INT(RND*3+1)
PSET(0,199),1'INT(RND*3+1)
PSET(319,199),1'INT(RND*3+1)
PSET(319,0),1'INT(RND*3+1)
Box 0,0,319,199
SUB Box(x1,y1,x2,y2)
IF x2-x1<1 THEN EXIT SUB
IF INKEY$="" THEN SYSTEM
x3=(x1+x2)*.5:y3=(y1+y2)*.5
p1=POINT(x1,y1)
p2=POINT(x2,y1)
p3=POINT(x2,y2)
p4=POINT(x1,y2)
IF POINT(x3,y1)=0 THEN PSET(x3,y1),(p1+p2+Rf*(RND*4))/(2+Rf)
IF POINT(x2,y3)=0 THEN PSET(x2,y3),(p2+p3+Rf*(RND*4))/(2+Rf)
IF POINT(x3,y2)=0 THEN PSET(x3,y2),(p3+p4+Rf*(RND*4))/(2+Rf)
IF POINT(x1,y3)=0 THEN PSET(x1,y3),(p4+p1+Rf*(RND*4))/(2+Rf)
IF POINT(x3,y3)=0 THEN PSET(x3,y3),(p1+p2+p3+p4+Rf*(RND*4))/(4+Rf)
Rf=Rf*.5
Box x1,y1,x3,y3'1
Box x3,y1,x2,y3'2
Box x3,y3,x2,y2'3
Box x1,y3,x3,y2'4
Rf=Rf*2
END SUB