[geeks] sgi i2 opengl/glut perf question

[Joshua D Boyd]

On Thu, Dec 13, 2001 at 07:57:40AM -0800, Daniel Johannsson wrote:
> I looked at some gfx comparisons at Ian Mapleson's site, and it looked like
> an onyx re2 isn't that much faster than a high impact at doing shaded tris.
> Is the big difference when it comes to texturing?  I'm a bit concerned
> about what will happen on the high impact box when I try to use more than
> 4mb of textures.  Will it just not work, or will there be a huge perf
> hit once it has to swap out textures for every frame draw?

It won't just fail.  It will either swap on ever frame, or it will resort to
software, I don't remeber which, and I don't want to take the time now to look
it up.

> Does an re2 have a lot more tram? I noticed that it supposedly has a
> lot more framebuffer, can 160mb really be true?

I believe the re2 takes up to to 16megs of tram.  IR on the onyx goes to 64, I 
think.

And yes, the 160meg frame buffer is currect.  Think about it.  1600x1200 
display is 1.92 million pixels.  I think that RE2 goes up to 1920x1280, which 
is 2.547 million pixels.  The RE2 uses 64bit color (which is 8 bytes), so write
there, a single frame is just short of 20 megs.  The RE2 is double buffered, so
now we are up to 40megs.  Now, I think (but perhaps am wrong) that the RE2 uses
the frame buffer for off screen rendering contexts (which is used for 
reflections in 3D scenes, as well as for rendering to a video output board), 
which will eat of more memory.  Plus, does one RE2 boardset support multiple 
heads?  If so, that is even more memory gone really fast. 

In short, you don't have to be too inventive to use up a lot of frame buffer.
The IR goes up to 320megs of frame buffer, and IR2 (used in the Onyx 2 and 3)
goes up to 640megs of frame buffer.



-- 
Joshua D. Boyd