- tiled grid
The horizontal lines are parallel but appear tilted. This apparently simple illusion was invented by Johann Zollner in 1860.
To New
# set default screen, pen and turtle values
ResetAll SetScreenSize [400 400] HideTurtle
SetSC Black SetPC Green SetPS 1 PenUp
End
To GridSq :Order :Side
# draw tile at each column x row position
LocalMake "Offset (1+:Order)/2
For (List "Col 1 :Order) [
For (List "Row 1 :Order) [
SetXY :Side*(:Col-:Offset) :Side*(:Row-:Offset)
Tile :Col :Row :Side] ]
End
To Tile :Col :Row :Side
SetH 90+180 *(Mod :Row 2)-90*(Mod :Col 2)
Back :Side/2 Right 90 Back :Side/2
PenDown Repeat 4 [Forward :Side Left 90]
ForEach "P [1 -1] [
Repeat 2 [
Left :P*22.5 Forward 0.46*:Side Back 0.46*:Side
Right :P*22.5 Forward 0.4*:Side
Left :P*22.5 Forward 0.46*:Side Back 0.46*:Side
Right :P*22.5 Forward 0.6*:Side Left :P*90]
Right :P*90 Back :Side Right :P*90 Back :Side Left :P*90] PenUp
End
To Go :Order
New
GridSq :Order 384/:Order
End