xm=xpixels(); ym=ypixels()
Do k=1,10000
   x=random(xm)
   y=random(ym)
   dx=random(51)-25
   dy=random(51)-25
   line color (random(15)+1)
   line (x,y,x+dx,y+dy)
Loop

open screen (1)
bitblt screen (0)
open screen (2)
x=100; y=75
dx=4; dy=4
Do
   select screen (2)
   bitblt screen (1)
   bitblt screen (1, x, y, 100, 100, 0, 0)
   select screen (0)
   bitblt screen (2, x-10, y-19, x+110, y+110)
   x=x+dx; y=y+dy
   If (x<0 Or x>xm-101) dx=-dx
   If (y<0 Or y>ym-101) dy=-dy
   key=readkey()
   If !key Continue
   If (key=27) quit
   key=wait key()
   If (key=27) quit
Loop