Path: utzoo!attcan!utgpu!watmath!watcgl!ksbooth
From: ksbooth@watcgl.waterloo.edu (Kelly Booth)
Newsgroups: comp.graphics
Subject: Re: clipping polygons to a viewport
Keywords: polygons,clipping
Message-ID: <11755@watcgl.waterloo.edu>
Date: 4 Oct 89 00:46:43 GMT
References: <120@csinc.UUCP>
Reply-To: ksbooth@watcgl.waterloo.edu (Kelly Booth)
Organization: U. of Waterloo, Ontario
Lines: 17

In article <120@csinc.UUCP> shal@csinc.UUCP (Shal Jain x848) writes:
>Am looking for a very robust algorithm/code for clipping polygons to a 
>rectangular viewport.

Foley and Van Dam's text also discusses this problem.  The classic paper
is

	Ivan E. Sutherland & Gary W. Hodgman
	Reentrant Polygon Clipping
	Communications of the ACM
	Vol 7 No 1 (January 1974) pp. 32-42

Beware:  There is one error in a diagram (a flowchart, I think) in the paper.
The appendix to the paper discusses the particular problem you pose (a concave
polygone which, after clipping, results in two or more disconnected polygonal
regions).  The solution requires sorting the points of intersection along each
edge of the clipping window/viewport to discover the various pieces.