to fractal_tiling
 ct cs ht setpensize 0.3
 updategraph 
 setFillTolerance 0.3
; disableLineSmooth 
 ;setfc rgb 1 1 0
 setpc rgb 0 0 0
 backc=rgb 1 1 1 
 let[[size 200]
     [f (sqrt (4-2*sqrt 2))/2]
	   [n0 10]]
 pu bk :size/2
 localmake "k0 1
 tile n0  :size (list (list pos Heading))
 make "k0 -1
 home  pu bk :size/2
 tile n0  :size (list (list pos Heading))
end
 
to tile :n :size :list1 [:k :k0][:list2 []]
 if :n==0 [stop]
 setfc rgb 1 n/n0*0.95  0
 if empty? :list1[(tile :n-1 :size/sqrt 2  :list2 0-:k [] ) stop]
 ;(show "list1 :list1)
 local [posn posn1] make "posn first :list1
 pu setpos first :posn seth last :posn
 ;comment[ 
 make "posn1 list pos heading
   rt :k*22.5 fd :size*:f
   if or not pixel == rgb 1 1 1 (signum xcor) == 0-:k0
   [setpos first :posn1 seth last :posn1
  (tile :n :size bf :list1 :k :list2 ) stop]
 setpos first :posn1 seth last :posn1
  ;]
; Tesselation
; [ 
   pd fd :size rt :k*135
   make "list2  fput list pos heading :list2
   fd :size/sqrt 2 rt :k*90
   make "list2  fput list pos heading :list2
   fd :size/sqrt 2 rt :k*135
; ]
 pu
 rt :k*22.5 fd :size*:f  
; setfc HSB 360*:n/10 1 1
; setpc backc
; fill
; (fill FILL_SURFACE) 
; (fill FILL_SMALL)
; (fill FILL_SMALL_SURFACE)
 (fill FILL_SMALL_TOLERANT) 
; (fill FILL_SMALL_SURFACE_TOLERANT)
 ;setpc 0 
; updategraph 
 (tile :n :size bf :list1 :k :list2 )
end