>> Yeah, I'm reading about it now. (Hmm, I guess I'm not the only person 
>> who still thinks 512 MB RAM is a lot. ;-)
> 
> For a games console it's probably enough.

Well, judging by the number of PS3 games... ;-)

> What do you hold in RAM 
> during a game?  All the 3D meshes and textures are on the GPU video 
> memory only*. Probably only the code, collision meshes, map data?  And 
> the PS3 OS is vastly simpler than Windows, so I doubt that uses up much 
> RAM.

That's rather perverse though. Are you telling it you need "at least 2 
GB RAM" to run M$ Office smoothly, but 1/8 of that is just fine for 
running extremely intensive game software?

> * When you write a game under Windows, you must keep all the GPU data 
> mirrored in normal RAM, because if the user Alt-Tabs to a different 3D 
> game, you need to refill the GPU memory quickly (and not go through some 
> long load-from-disk process) when the user comes back to your app.  On a 
> games console you don't need to do this, because (at least on the PS3) 
> you have to quit one game before you can go into another.

Now that you mention it, if I Alt-Tab out of TF2, my PC locks up for 
about 30 seconds. (As in, I get a black screen for 30 seconds.) Then 
Windows comes up - possibly in the wrong resolution. Switching back to 
TF2 is similarly slow. Go figure...

> There was a nice paper I read in a book a while back (one of the GPU 
> gems series I think), where some algorithm was explained for doing 
> correct multi-level reflections on the GPU.  It was quite complex, 
> involving generating lots of cube-maps with depth and texture 
> information and some ray-tracing steps in a pixel shader.  In the end 
> they compared the output with a real raytracer, and the results looked 
> identical, but the GPU version ran at about 10fps IIRC with something 
> like 4 levels of reflection.  The real raytracer (Maya I think) was 
> measured in minutes.

As I understand it, technologies like CUDA allow you to run arbitrary 
code on a GPU. So no need for convoluted trickery to convince the GPU 
that your proplem is just like texture mapping, just feed it the actual 
calculations you want it to do. (Of course, it runs arbitrary code, that 
doesn't necessarily mean it runs it *fast*.)

Of course, CUDA is *only* for nVidia GPUs. (Wouldn't surprise me if ATi 
had developed something similar.) I wonder if this will be like the old 
3Dfx API where eventually everything gravitates towards a single API 
that works for any GPU?

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

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