[rescue] SGI Indy for $25?

[Joshua D Boyd]

On Thu, Dec 13, 2001 at 07:56:46PM +0100, Carl-Johan Schenstrom wrote:
> On Thu, 13 Dec 2001, Joshua D Boyd wrote:
> 
> > > If it's an R5K I believe you're better off with an XL24, even for 3D.
> >
> > Would you care to say more about that?  I know that the r5k is faster at
> > geometry transformation than the XZ, but doesn't the XZ offer other features
> > (depth buffering comes to mind, but I'm being to lazy to check).
> 
> Disclaimer: I'm probably out of my depth here because I know nothing of
> these things, at least compared to you.
> 
> Yes, you only get Z-buffering with the XZ. If this is important, the XZ is
> obviously a better choice. It tends to be quite expensive, though, and may
> even make some operations (geometry and lightning) slower than using the
> R5K CPU.

Yeah, I was looking on ebay a bit ago, and the XZ boardset for indy seems to be
about the same price as a lowend Indigo2 Extreme these days.  So, it seems that
the only reasonable upgrades to perform to an Indy would be Ram (which can be
reused later) and perhaps an upgraded SCSI card (especially if you happen to 
have lucked out and gotten a machine with something better than VINO video IO).

Now, as to the geometry and lighting being slower on the XZ than the R5k, I 
would have thought that SGI would have included a software switch allowing you
to disable the geometry processing.

Anyway, looking around, I see that XZ isn't as good at 2D as the XL.  Well, 
that sucks.  So, I wonder how the depth buffer performs in software versus 
hardware.  In addition to faster hidden surface removal, there are other things
that you can use the depth buffer for.  For instance, it is handy to be able to
read it if you want to save your screens with depth information for later 
processing.  It also can be handy for cell shading systems.  However, these 
tasks listed are already tasks that probably wouldn't be real time.

Yeah, I guess almost anyway you look at it, the XL is better for r5ks.

Wait, I just thought of a case where the XZ would be better.  Consider that you
have a simulation that doesn't require heavy graphics to display, but it does
require a lot of CPU power.  Then, having the rendering handled by the XZ board
will free up more CPU power than the XL board.

Alright, that is stretching.  I'll be quite now.
 
-- 
Joshua D. Boyd