# Main Command: Go
# Dust by Guy Walker
# www.logoarts.co.uk

to new
  # set default screen, pen and turtle 
  ResetAll SetScreenSize [400 400] HideTurtle 
  SetSC Black SetPC Green SetPS 1 PenUp 
end

to dust
  Home Right Random 360 Forward :Max Make "Col 0
    While [:Max < 182] [ 
      While [:Col = 0] [
      SetPC Black Dot Pos  # erase previous dot
      SetH Towards [ 0 0 ]
      Left 30 Right Random 420 Forward 1
      Make "Col Vicinity
      SetPC Yellow Dot Pos]
    Make "MaxNew 2 + Distance [ 0 0 ]
  If :MaxNew > :Max [ Make "Max :MaxNew] 
  Dust ]
end

to vicinity
  # check occupation of surrounding pixels
  # return '1' if neighbouring dust is present
  For [I -1 1] [
    For [J -1 1] [
    Make "R Item 1 FindColor List :I+X :J+Y 
    If :R = 255 [Output 1] ] ]
  Output 0
end

to go
  New SetPC Yellow
  Dot Pos  # draw a seed dust speck
  Make "Max 4
  Dust
end