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From: jbickers@templar.actrix.gen.nz (John Bickers)
Newsgroups: comp.sys.amiga.programmer
Subject: Re: Clicking on irregular shapes?
Message-ID: <1757.tnews@templar.actrix.gen.nz>
Date: 29 Mar 91 20:58:34 GMT
References: <1991Mar27.212214.6204@orfeo.radig.de> <2710@sirius.ucs.adelaide.edu.au> 
 <20181@cbmvax.commodore.com> <1991Mar29.022042.14110@leland.Stanford.EDU>
Organization: TAP, NZAmigaUG.
Lines: 22

Quoted from <1991Mar29.022042.14110@leland.Stanford.EDU> by mmaston@leland.Stanford.EDU (Michael Maston):
> object on the screen has been chosen by a mouse-click.  Now this is pretty
> straightforward for boxes, lines, circles and even ellipses, but how does
> one do this with say an object drawn with a freehand tool?  I have experimented

    One approach is to determine if the point is within a polygon or
    not. First check the point against the extent of the polygon, and
    if it's in, then count how many edges of the polygon a line from
    the point to one edge of the screen intersects.

    Odd and it's inside, even and it's outside.

> Anyway, are there good references on this type of algorithm that the great

    There's comp.graphics. I think the above approach is in the FAQ
    posting there. The FAQ also contains a list of references for various
    things.

> Michael Maston
--
*** John Bickers, TAP, NZAmigaUG.        jbickers@templar.actrix.gen.nz ***
***         "Patterns multiplying, re-direct our view" - Devo.          ***