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From: paul@torch.UUCP (Paul Andrews)
Newsgroups: comp.graphics,sci.math,comp.sources.wanted
Subject: Re^2: looking for a fast ellipse algorithm
Message-ID: <236@torch.UUCP>
Date: 23 Feb 89 17:38:36 GMT
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Organization: TORCH Computers Ltd., Cambridge, England
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Just one thing about an ellipse drawing DDA: Unlike the circle DDA you get
power-of-4 terms. This means that to do this accurately for a 16bit coordinate
space you need 64 bit arithmetic. This really needs to be done in assembler.
(Of course if you use a 32 bit coordinate space you need 128 bit arithmetic).

If you are going to draw arcs of ellipses, you will have fun computing the
start and end points. You can do this with floating point trig (but then
thats slow), or you can use the CORDIC method (Someone got a reference?). And
you may find it useful to define 45 degrees as the angle between a line drawn
from the center of the ellipse to a corner of its bounding rectangle and one
of its axes. i.e. its only really 45 degrees for a circle. After that it gets
progressively squashed.

As far as I am aware, drawing ellipses with axes that are not horizontal/
vertical is somewhat harder. Do any of the references given so far address
this problem?

- Paul