Xref: utzoo comp.graphics:1977 comp.sys.ibm.pc:13143
Path: utzoo!mnetor!uunet!mcvax!unido!ecrcvax!johng
From: johng@ecrcvax.UUCP (John Gregor)
Newsgroups: comp.graphics,comp.sys.ibm.pc
Subject: Re: COMPLICATED PROBLEM; ONLY INTELLIGENT PEOPLE SHOULD READ
Message-ID: <513@ecrcvax.UUCP>
Date: 14 Mar 88 02:31:10 GMT
References: <5740@cit-vax.Caltech.Edu>
Reply-To: johng@ecrcvax.UUCP (John Gregor)
Organization: ECRC, Munich 81, West Germany
Lines: 29

In article <5740@cit-vax.Caltech.Edu> gtchen@tybalt.caltech.edu.UUCP (George T. Chen) writes:
>Does any of the previously mentioned algorithm work with overlapping
>polygons?  For example, consider the grid
>
> [ Grid deleted ]
>
>Most algorithms (including the odd-even boundary method) will consider
>the diamond region between 2 and 5 to be outside the polygon although
>it's suppose to be inside.
>
>Comments?

The non-zero winding number rule will completely fill the polygon.
Like the even-odd rule, to determine if a point is "inside" take a ray
from that point to infinity.  For each ray-edge intersection increment
the intersection count if the edge passes from left to right, and subtract
one if the edge passes from right to left.  If the count is 0, then the point
is "outside" the polygon.

See Adobe's Red Book (Postscript Reference Manual) for a couble of sample
pictures.



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John Gregor                                     johng%ecrcvax.UUCP@germany.CSNET