Animated PostScript

anim.ps

%!PS
%%BoundingBox: 0 0 320 240

% gv -infoSilent anim.ps

/Courier findfont 12 scalefont setfont

/sleep { 100000 mul {} repeat } def

/x 100 def
/y 50 def
/r 15 def
/x_ 2 def
/y_ 1 def
/f 0 def

{	
	% x bounce
	x r sub 0 lt x r add 320 gt or {
		/x_ x_ -1 mul def
	} if

	% y bounce
	y r sub 0 lt y r add 240 gt or {
		/y_ y_ -1 mul def
	} if
	
	% move circle
	/x x x_ add def
	/y y y_ add def
	
	% clear page
	1 setgray
	0 0 320 240 rectfill

	% draw circle
	newpath
	x y r 0 360 arc
	1 0 1 setrgbcolor
	fill

	10 10 moveto
	0 setgray
	(frame            ) dup 6 f 10 string cvs putinterval show
	
    flushpage

	10 sleep
	
	/f f 1 add def
} loop