p_fire = 0.00002
p_tree = 0.002
#
len f[] 102 * 102
len p[] len f[]
gbackground 100
gclear
for r = 0 to 99 : for c = 0 to 99
   i = r * 102 + c + 104
   if randomf < 0.5 : f[i] = 1
.
timer 0
#
subr show
   for r = 0 to 99 : for c = 0 to 99
      i = r * 102 + c + 104
      h = f[i]
      if h <> p[i]
         if h = 0
            gcolor 100
            gcircle c + 0.5 r + 0.5 0.6
         elif h = 1
            gcolor 151
            gcircle c + 0.5 r + 0.5 0.5
         else
            gcolor 9 * 100 + (18 - 2 * h) * 10
            gcircle c + 0.5 r + 0.5 0.5
         .
      .
   .
.
subr update
   swap f[] p[]
   for r = 0 to 99 : for c = 0 to 99
      i = r * 102 + c + 104
      if p[i] = 0
         f[i] = 0
         if randomf < p_tree : f[i] = 1
      elif p[i] = 1
         f[i] = 1
         s = p[i - 103] + p[i - 102] + p[i - 101]
         s += p[i - 1] + p[i + 1]
         s += p[i + 101] + p[i + 102] + p[i + 103]
         if s >= 9 or randomf < p_fire
            f[i] = 9
         .
      elif p[i] = 4
         f[i] = 0
      else
         f[i] = p[i] - 1
      .
   .
.
on timer
   show
   update
   timer 0.2
.