link graphics
global part,size
procedure main()
   size:=400
   knee:=[0.30, 0.22]
   part:=[
   	[knee,[[ 0.20,-0.25],[ 0.25, 0.20]]],
   	[knee,[[-0.25, 0.20],[ 0.20, 0.25]]],
   	[knee,[[ 0.70, 0.10],[-0.10, 0.70]]]
   	]
   part:=[
   	[knee,[[ 0.70, 0.10],[-0.10, 0.70]]],
   	[knee,[[ 0.20,-0.25],[ 0.25, 0.20]]],
   	[knee,[[-0.25, 0.20],[ 0.20, 0.25]]]
   	]
   WOpen("size=" || size || "," || size,"bg=very light gray") |
   	stop("can't open window")
   Fg("light weak green")
   drawRecursively([[0.0,0.0],knee])
   WriteImage("lightfern.gif",0,0,size,size)
   WClose()
end

procedure mpyvm(v,m)
return [v[1]*m[1,1]+v[2]*m[2,1],v[1]*m[1,2]+v[2]*m[2,2]]
end

procedure addv(u,v)
return [u[1]+v[1],u[2]+v[2]]
end

procedure drawRecursively(l)
local r
if integer(l[1][1]*size)=integer(l[2][1]*size) & 
   integer(l[1][2]*size)=integer(l[2][2]*size) then {
	DrawPoint(l[1][1]*size,l[1][2]*size)
} else {
     every r:=!part do 
     	drawRecursively ([
		addv(r[1], mpyvm(l[1],r[2])),
		addv(r[1], mpyvm(l[2],r[2]))
	])
     DrawLine(l[1][1]*size,l[1][2]*size,
	l[2][1]*size,l[2][2]*size)
}
return
end