Excellent site; the figure library is especially inspiring.
Making irregular canvasses (that is, not rectangular) started
with one for Penrose's triangle and eventually led to my failing
a college painting class... the professor said they were novel,
but had no artistic merit. I said that's fine, some people just
can't wrap their heads around them: the whole class laughed and
the humiliation was never forgiven...
It didn't stop me from pursuing them, though!