Re: [cc65] TGI pixel aspect ratio

From: Groepaz <groepaz1gmx.net>
Date: 2009-10-29 17:14:33
On Donnerstag 29 Oktober 2009, Ullrich von Bassewitz wrote:
> On Thu, Oct 29, 2009 at 03:10:12PM +0100, Oliver Schmidt wrote:
> > However I disagree with your statement that the 'pixel aspect ratio'
> > is unrelated (not even talking about 'completely unrelated') to the
> > resolution, size or aspect ratio of the display.
>
> No need to duel each other:-)

=P

> The idea to have the driver publish an aspect ratio is a good idea. For
> TGI, we will use a 16 bit fixed point number (8 bits before and after the
> decimal point) that tells how to make circles on the standard display,
> taking the resolution and the side ratio of the CRT into account.
>
> The sine/cosine routines will return the same fixed point format.

mmmh i am not sure if 16bit isnt a bit overkill... i think its worth to test 
wether an 8bit 2.6 format isnt enough... that would be quite a bit faster, 
and allow to use simple lookup tables instead of trig. functions for sin/cos

oh and to be pedantic again, the correct values also depends on the output 
format (pal vs ntsc) =) 
http://codebase64.org/doku.php?id=base:pixel_aspect_ratio gives some basic 
info on how to calculate them properly (and also how to calculate an 
estimate, which still works for most practical purposes)

-- 

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Received on Thu Oct 29 17:13:11 2009

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