From: Martin DeMello <martindemello@...>
Date: 2005-05-06T18:54:25+09:00
Subject: Re: Ruby-tk question

Logan Capaldo <logancapaldo@gmail.com> wrote:
 
> One last note, this function is gonna rotate like it was on a
> cartesian plane (origin in the middle), if Tk's Canvas is like every
> other computer coordinate system i've come across, the coordinates are
> gonna be only in quadrant IV with the y-value negated, so you may have
> to keep that in mind before just  pasting this code in.

Usual idiom is to translate the coordinates so that the point you want
to rotate around becomes (0,0), rotate, then translate back.

m.