Path: chuka.playstation.co.uk!news
From: Jake Turner <jaket@revolution.co.uk>
Newsgroups: scee.yaroze.freetalk.english
Subject: Re: Triangles, Quads???
Date: Mon, 12 Oct 1998 20:42:16 +0100
Organization: PlayStation Net Yaroze (SCEE)
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Karsten Wutzke wrote:

> What's better?
> Make the models from triangles or quads?
>
> It doesn't make a difference (to me) from an artistic point of view,
> but what about the performance? I looked at the TMD
> primitive structures ilen/olen stuff from which I derived, that
> quads are the faster the more "real" quads, e.g. no simulated
> triangles there are...
> The problem is: I'm just guessing around!
>
> If I took the TMD structs:
>
> G_3T (triangles, gouraud,textured, lights on): ilen 6 - olen 9  and
> G_4T (quad(r?)angles, gouraud,textured, lights on): ilen 8 - olen 12
>
> Now say I have one torus object each:
>
> G_3T:   (256 vertices ,) 512 primitives/polygons/triangles
> G_4T:   (256 vertices ,) 256 primitives/polygons/quads
>
> Can I calculate or approximate the possible work to be done as
> follows...
>
> (no. of prims) * (ilen) + (no. of prims) * (olen) =  X
>
> G_3T:   512 prims * 6 + 512 prims * 9 =  7680
> G_4T:   256 prims * 8 + 256 prims * 12 =  5120
>
> 7680 / 5120 = 1.5  -> triangle model ~50% slower???
>
> Hmmm... maybe I should just check the frame rate...
> Anyway what do you think?
> What's the playstation doing? Does it convert triangles to quads or
> quads
> to triangles ? Does it matter?

The PlayStation is more native to quads than triangles, so quads are
nearly same speed as triangles (on PlayStation).

However, quads are a bad approximation to a curved surface or 3D models
(except planar surfaces) in general.  Also, most art packages do not
output quads e.g. 3D Studio MAX is almost exlusively triangle based.

Also, note with quads it is easy to get an illegal polygon e.g. not a
flat plane, whereas this is impossible with triangles (excluding zero
area objects).

So I would go for triangles, but try and use quads where possible.  On
the PlayStation you will have to subdivide large polygons to overcome
its inaccuracies, so not much of gain there either

Hope this helps

Jake Turner