Hermann Grid

by Stan Munson

Do you see dark spots at the intersections? There are none! It’s an optical illusion.

The image is a blow-up of background pattern 7 that creates the grid.

Hermann-grid.lgo

TO MAIN
	DRAW
	CT
	PRINT "|Hermann Grid: Do you see dark spots at the intersections?|
	PRINT "|There are none! It's an optical illusion! The image is a |
	PRINT "|blowup of background pattern 7 that creates the grid.|
	FOREVER [RANDOM.HERMANN.GRID WAIT 5000 DRAW]
END

TO RANDOM.HERMANN.GRID
	CLEAN SETBG PICK [0 1 2 3 4 5 6 8 9 12 13]	; Not all colors work well
	SETBGPATTERN 7
	TELL 0 HT
	MAKE "HERMANN SNAP 29 21
	TELL :HERMANN
	MAKE "SIZE 2
	ST
	REPEAT 7 [SETTS :SIZE MAKE "SIZE :SIZE + 2 WAIT 100]
END

MAIN

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Procedure	MAIN
Description	Optical illusion
Level	Intermediate
Tags	Art, Science