| From: | Joseph Fenton |
| Date: | 18 Aug 2000 at 17:49:48 |
| Subject: | Re: G3 & CGFX |
Alan Buxey wrote:
>
> hi,
>
> > You've gotta be kiddin... That's the framerate I reach on my ATI Rage128 in
> > 640*480*32. No, we're talking much bigger here... Something around 40 or 50 :)
>
> with a 21Mb/s bandwidth - as has been suggested for Mediator - then the most
> you can get through at 640x480x16bit is 35 fps
Only if you have to update the whole screen by hand every frame.
This is not the case... usually, you have already precached the
most commonly used textures for the level on the card, and you only
have a very small status bar to update by hand... the rest of the
scene is generated on the card by the 3D processor from the
vertex an lighting info sent. So the only real data trnasferred
is the triangle info and the odd texture not already cached.
21MB/s can therefore do 3D MUCH faster than 35 FPS as long as
the on-card 3D processor is fast and most all the textures are
cached. The bandwidth at this point limits how many triangles
per scene you can update per frame; lower bandwidth means fewer
triangles - a blockier scene, but still fast and looking good;
more triangles means more refined models, which can actually
make it run slower if you send more triangles than the 3D processor
can handle in a frame.
The Nintendo 64 sort of falls in this area... ever notice that
nearly all N64 games are blocky? The N64 cannot process as many
triangles per frame as the Playstation (the original, not the new
one); it cannot process as many, but they look better. This
means that N64 programmers have to decide how best to use the
triangles so that it looks as good as possible; one way is the
almost ever present "fog" in N64 games... don't render triangles
in the distance, just put some fog back there to obscure where
they'd have been, then use those triangles to make the foreground
look better. Turak is a great example of this. The Playstation
has more triangles per frame to work with, they just don't look
as good; so a Playstation game will have less fog and try for
more detailed characters than you see in N64 games. Compare
The Tekkan characters to the Mario 64 characters... BIG
difference... the Tekkan characters are very smooth from lots
of polygons, while the Mario 64 characters often appear to be
at most 3 triangles.
So, to make a long story longer :^}, you can make a Zorro 2
version of the latest GeForce card that can only transfer
3 MB/s and make GREAT looking and playing games as long as
you program around the limit in the number of triangles
per frame you will be able to change. Having On-card transform
and lighting engines makes even that less a problem now. You
tell the card only how groups of triangles change (rotate, etc),
and it'll do all that for you. This makes the bandwidth you
need even smaller.