link graphics, randomiz
global color,nwcolor,secolor
procedure main()
   local R,r,x,y,lightcolors,darkcolors,W,H
   W:=300
   H:=300
   randomize()
   WOpen("size="||3*W||","||3*H,
   	"bg=black") |
   		stop("can't open window")

   lightcolors:=[
   	"yellow","green","cyan",
   	"white"
   	]
   midcolors:=["yellow","green","blue","magenta","red"]
   darkcolors:=[
   	"blue","black","red" ]

   Fg("black")
   
   every 1 to 40 & (x:=?W,y:=?H) do {
   	R:=5+?(W/5)
   	secolor := "very dark "||?darkcolors
   	nwcolor := "very dark "||?lightcolors
   	color := "very dark "||?midcolors #if ?0 < 0.5 then nwcolor else secolor
   	every r := 0 to R by 1 & i:=0 to 2 & j:=0 to 2 do {
   		ball(x+i*W,y+j*H,integer(sqrt(R*R-r*r)))
   	}
   	Fg("black")
   	every 1 to H/50 & DrawPoint(W+(0 to W),H+?(H+1)-1) 
   }
   every 1 to H/2 & DrawPoint(W+(0 to W),H+?(H+1)-1)
   CopyArea(W,H,W,H,0,0)
   WriteImage("balls.gif",0,0,W,H)
   WClose()
end


procedure ball(x,y,r)
   local nw,se
   static d
   initial d:=1
   #r:=r-d
   nw:= nwcolor
   se:= secolor
   Fg(nw)
   FillCircle(x-d,y-d,r)
   Fg(se)
   FillCircle(x+d,y+d,r)
   Fg( color)
   FillCircle(x,y,r)
return
end