RE: [Algorithms] VIPM on a machine with DMA :)

[Tom F. <to...@mu...>]

> From: Jamie Fowlston [mailto:j.f...@re...]
> 
> 
> Still have to DMA the vertex data, which is larger for VIPMed 
> models (am I
> right? I've not implemented VIPM, but think I've understood 
> the general idea).

No, the vertex data is precisely as big as your most-detailed model - that
is, the most detailed model you want to draw that frame (or that instance or
whatever). There is zero bloating of vertex data.

The index data is indexed lists, so that's very slightly bloated from
indexed strips in some cases, but probably not so you'd notice - indices are
tiny compared to the vertices anyway. And the collapse/expand info is
moderately big thinking about it (12 bytes per collapse on average I think -
I can't remember), so it may not be a win to do the collapse/expand on the
"non-CPU unit" - who can tell? It's pretty quick on both to be honest.

> So total transfer is larger than it would be for non-VIPMed 
> model. We're
> expecting to be DMA speed constrained rather than draw speed 
> constrained.

Indeed, that's what I woudl expect too - the DMA seems to be the hardest
thing to get right about the machine. But fortunately there is no bloat. Go
and read Charles Bloom's excellent VIPM tutorial (one day I'll get around to
doing my own - actually, there's not much point - it'll be identical to
Charles'). (http://208.55.130.3/3d/ - sixth link down).

> Have you actually implemented VIPM on... that machine? :) Some sort of
> algorithms-style section in the support newsgroup would be 
> nice, and I could
> stop waffling and talk specifics.... :) Talk about LoD would 
> be useful. I'll
> post something....

No, I haven't actually played with that machine yet, except in my head from
the specs (and I'm not on the newsgroup or anything). Busy enough playing
with the Dreamcast!

I have implemented it on the PC, using similar sorts of semantics -
Optimised VBs. There, DMA speed (well, AGP bus speed) is king as well.

> I know some stuff about other consoles... but AFAIK, I can't 
> say which or how
> much. Aren't NDAs fun? :)

Grrrr. :-)

> Jamie

Tom Forsyth - Muckyfoot bloke.
Whizzing and pasting and pooting through the day.