Path: chuka.playstation.co.uk!news
From: alex@teeth.demon.co.uk (Alex Amsel)
Newsgroups: scee.yaroze.programming.3d_graphics
Subject: Re: OT's - how do they work?
Date: Sun, 19 Oct 1997 17:17:42 GMT
Organization: Into Beyond
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On Fri, 17 Oct 1997 16:33:49 +1300, James Russell <jruss@ibm.net> did
quoth at me:

>I'm writing up a 2D graphics tutorial and although I've used OT's to get
>my stuff working, it was all straight from the examples. Closer
>inspection revealed that an OT is just an array of OT_TAGS, which are
>just 32 bit wide bit fields:
>
>unsigned p:24;
>unsigned num:8;
>
>So what I want to know is:
>
>What is p? What is num?

p is a 24 bit pointer to the next OT_TAG. num is a primitive code from
which the ps-x knows what data immediately follows the OT_TAG.
e.g. POLY_FT4, POLY_GT3 and similar

>How do they specify which GPU packets get sent, and in what order? How
>is the linked list maintained?

Presuming you know how the basic OT works, within each 'slot', the
last polygon placed in each slot is the first polygon drawn of that
slot. This can be useful to know (especially when inserting OTs into
existing OTs).

>How are they affected by 2D graphics?

No different AFAIK, except you effectively declare the sprite priority
as you no longer deal with polygons.


Regards, 

Alex Amsel

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