Path: chuka.playstation.co.uk!news
From: Andreas Schrattenecker <"Andreas Schrattenecker">
Newsgroups: scee.yaroze.programming.3d_graphics
Subject: Re: HELP:small planar quads
Date: Thu, 15 Jan 1998 01:31:55 +0100
Organization: PlayStation Net Yaroze (SCEE)
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References: <69ilnb$c4e1@emeka.playstation.co.uk> <34BCEC93.4581@jk.uni-linz.ac.at> <01bd212d$f848afc0$77e16dc0@ulthar.han.de>
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Roland Boettcher wrote:
> 
> I made a tmd from the '.ply' you supplied and watched it using tmdview.
> Both quads display fine as long as you look at them at a "reasonable"
> angle. But when the angle gets such that the quad far away is just a line
> due to perspective it disappears sometimes.  It flashes when you are moving
> to it. Is that what you mean?
yes
> If so, I guess this is because of inaccuracies of integer calculation.
> 
> Roland

Yes, it seems so.
But i wondered why this doesnt happen with triangles.

I tested following: 

@PLY940102      
#
6     1       2
#
0       0       1280
0       0       1536
256     0       1536
0       0       5120
0       0       5376
256     0       5376
#
0       -1.0    0       
#
0       4       5       3       0       0       0       0       0
0       1       2       0       0       0       0       0       0

Displaying only the triangles (first 3 vertices), which are
taken for "visible-detection" (no backface culling)
in quads -> same errors (i was a bit surprised)

But this seems to have no effect in triangle-meshes( at least 
i never had one missing triangle in my meshes), so its better
i think(less triangles to display).

But it shouldnt happen in planar quad-meshes, and you lose
a lot of performance correcting this outside the libraries.


Andreas Schrattenecker