See also op art and patterns/textures.
Contributed by Florian Hardwig
Contributed by Marianna Mooney
Contributed by Joana Correia
Contributed by Darius Kisielius
Contributed by Anna Farkas
Contributed by Johannes Stoll
Contributed by Mucho
Contributed by Rodrigo Saiani
Contributed by Stephen Coles
Contributed by Dafi Kühne
Contributed by Lluís Serra