RE: [AD] Porting Allegro to the PS2

[Shawn Hargreaves <shargreaves@xxxxxxxxxx>]

Joshua Walker writes:
> *OMG SHAWN HARGREAVES IS A PS2 DEVOPLER!*

I used to be, but then I saw the error of my ways and became 
an Xbox lover :-)

http://www.talula.demon.co.uk/motogp/index.html

> I've only had the thing for a week so If I error on the 
> architecture, it's because I've only read the EEOverview 
> manual and the GS Manual. I have the VU Manuals in 
> my palm and have yet to read them. EEcore is next after that

If they are anything like the developer manuals we got, the
EE core one is a total waste of time. You're unlikely to ever
need to write asm for that (concentrate on the VU's for all
your hand coding) plus it is such a confusingly written mess
with these huge verbose descriptions of machine code 
instructions that are almost identical, it's very hard to 
make any sense out of it (actually all the manuals suffer
from that problem). On the EE side, though, I'd just stick
to gcc or get a generic MIPS book if you ever do need to drop
down to asm.

> I stand corrected, I remeber them being very tiny. But I love 
> machine code. Anyway I have some libs sony provided for them, 
> I was just gonna use those...

We didn't have any VU code except what we wrote ourselves, and
no CPU side stuff except a bit of code for building up DMA,
VIF, and GIF tag structures that turned out to be incredibly
buggy :-) Maybe they've improved things since, though.

The VU processors are certainly fun to program in a sick and 
twisted kind of a way :-) You can do some very satisfying 
stuff with those lovely 4-vector parallel registers, but the
integer and control construct side is too limited to be 
anything other than frustrating (for instance you can't
actually build up new GS tags in VU programs because the 
integer ops are only 16 bit).

My magnus opus was a lit+envmapped bezier patch tesselator 
which ran entirely in VU1, and I did enjoy coding that, but
it made my head hurt so much that I was glad to say goodbye
to the thing and go back to more normal types of programming!

The Xbox (or PC GeForce3) vertex and pixel shaders can do
most of the same cool stuff you'd want to put in VU1, but
without anywhere near the amount of hassle. So you actually 
have a bit of time left over to decide what you want to _do_
with the graphics, rather than spending months just writing
the basic clipping and lighting code :-)

Good luck with it, anyway, and don't let my jaded/cynical
opinion put you off!


-- 
Shawn