# Main Command: Go 7
# Negative Circles 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 init :order
  # global values
  Make "Size 378
  Make "CellSize :Size/:Order
  Make "OffSet :CellSize/2 - :Size/2
  Make "Side :CellSize/1.4
end

to gridd :m :n
  # return X Y screen position
  Make "X (:M*:CellSize) + :OffSet
  Make "Y (:N*:CellSize) + :OffSet
  Output List :X :Y
end

to drawgrid :order
  # draw M x N array of squares
  For (List "N 0 :Order-1) [
    For (List "M 0 :Order-1) [
    SetPos Gridd :M :N
    Cross :Side] ]
end

to go :order
  # draw grid of squares
  New Init :Order
  DrawGrid :Order
end

to cross :side
  # square (side x side) drawn from centre (tp)
  Repeat 4 [
    PenUp Forward 0.25*:Side PenDown Forward 0.75*:Side 
    PenUp Back :Side Left 90]
end