Posted-Date: Sun, 2 Feb 1997 20:25:31 -0600 (CST)
Message-Id: <199702030225.UAA22378@mail.texoma.net>
From: "Mark S. Teel" <mteel AT texoma DOT net>
To: "Benjamin D Chambers" <chambersb AT juno DOT com>
Cc: "DJGPP" <djgpp AT delorie DOT com>
Subject: Re: ellipses at an angle
Date: Sun, 2 Feb 1997 20:28:15 -0600
MIME-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit

>that: picture an ellipse leaning against a wall, what algorithm would 
>I
>use to draw that?
>
>Shawn Betts
>
:Well, you could use the original definition of an ellipse (that is, from
:any point on the ellipse, the sum of the distances from that point to the
:two foci equals 1).  The math gets a little messy though.

No!  This is not even the definition of an ellipse parallel to a coordinate
axis!
The general equation for an ellipse is:

Ax^2 + Bxy + Cy^2 + Dx + Ey + F = 0, B^2 - 4*A*C < 0.

If B == 0, then this reduces to an ellipse parallel to a coordinate axis.

MST