Path: chuka.playstation.co.uk!news
From: Jim <jim@micronetics.com>
Newsgroups: scea.yaroze.programming.3d_graphics
Subject: Re: Messing with the primatives
Date: Wed, 20 Aug 1997 10:06:23 +0100
Organization: PlayStation Net Yaroze (SCEE)
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Tim O'Neil wrote:

> If you display these primitive values (olen, ilen) before they are
> linked via GsLinkObject4 (or whatever it is), they correspond to the
> values that you set them to, but if you go into the 'tmd' pointer of the
> GsDOBJ2 structure and grab them after they have been linked, these two
> values are changed.  It only seems to modify the very first primitive
> packet for a given tmd header.  Was just wondering what this represents,
> because it is the only thing that is keeping me from bypassing that
> routine.

Your correct, GsLinkObject4 does a few things. One of them being 
the modification of the first ilen and olen params.  For the first
primitive this value represents a count of 'like' primitives to follow
this one.  It all goes towards speeding it all up.

*((ushort *)tmdprims) = primcount;

I have something akin to this in my code and completely bypass
GsLinkObject4.


>   I suppose another thing that makes me wonder about it is that even if
> you go in later and change the data in the primitive all around (save
> the stuff that has been modified) it will still work fine, but if you
> hammer these values back to what they were it will bomb.  

Its possibly crashing when you change the values back because it could 
still be drawing the tmd.  A lot of the drawing functions are non
blocking. 
So you could modifying some data while it is being operated on.

A solution to this would be to double buffer your tmds.  Wastes space.

I just put some menial code (next frames Ai, collision detection. etc..
) 
in-between the drawing and modify code to ensure that the data is no
longer 
being used.

Just a stab in the dark mind.

-JiM