[A89] Re: filling ellipses

To: assembly-89@lists.ticalc.org
Subject: [A89] Re: filling ellipses
From: Olle Hedman <oh@hem.passagen.se>
Date: Mon, 09 Jul 2001 04:07:07 +0200
Reply-To: assembly-89@lists.ticalc.org

At 02:31 2001-07-09, you wrote:
>Now, IF you were to get the Bresenham ellipse algorithm that Olle pointed
>out to work -- you'd have to find another implementation, since the one Olle
>pointed out seems to have not worked when you tested it -- and IF you
>changed it to use lines, as was suggested, it STILL would not work with XOR!
>That's because, as long as you could have two horizontally or vertically
>adjacent pixels, then you're bound to have overlapping lines.  Once again,
>XOR does not like overlap.

You could change the bresenham ellipse, just sligthlty, to only draw the 
lines when it changes in y. (if you use horizontal lines)
then it would work with xor, since it would never overlap. not very 
advanced to modify it too (if only one would find a working bastard, 
couldn't find where this was wrong, and I'm leaving home now for two weeks)
have to move the draws, to draw in the if-statements right before where y 
and x or only y, changes.  and no draw when only x changes.
and much much faster and much much much much more memory efficiant, then 
your double buffer sollution.

///Olle

Follow-Ups:

[A89] Re: filling ellipses

From: Olle Hedman <oh@hem.passagen.se>