Path: utzoo!attcan!uunet!dg!mpogue
From: mpogue@dg.dg.com (Mike Pogue)
Newsgroups: comp.graphics
Subject: Re: How does pr_vector() work ?
Message-ID: <343@dg.dg.com>
Date: 13 Mar 90 15:13:51 GMT
References: <1990Feb25.222157.26389@allgfx.agi.oz> <38280@cornell.UUCP>
Reply-To: uunet!dg!mpogue (Mike Pogue)
Organization: Data General, Westboro, MA.
Lines: 22

In article <38280@cornell.UUCP> klassen@gvax.cs.cornell.edu (R. Victor Klassen) writes:
>In article <1990Feb25.222157.26389@allgfx.agi.oz> shn@allgfx.agi.oz (Si-Hanh NGUYEN) writes:
>>
>>Does anybody know the detailed algorithm used in pr_vector() of Sun Pixrect ?
>>The manual says that "pr_vector draws balanced vectors. (The technique used
>>is to balance the Breshenham error term)".
>>
>

  Note that a very simple way to "balance" the error term involves reversing the end
points before feeding them to Bresenham's algorithm, when the vector is in one of 4 octants
(it doesn't matter which 4).

  This will guarantee that (A,B) = (B,A), and avoids writing code for 8 octants (and the
associated balancing required).  The disadvantage is that the line is drawn "backwards"
in those 4 octants.  Is this a problem?  In my experience, since only one line is drawn at a time,
no.

Mike Pogue
Data General

Speaking for myself, not my company....