Re: GIS

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Angus Dorbie (dorbie++at++sgi.com)
Fri, 03 Sep 1999 11:51:15 -0700

Mark Aubin wrote:
>
> On Sep 3, 5:48pm, Fernando Mato Mira wrote:
> > Subject: Re: GIS
> > At 07:05 PM 9/2/99 -0700, you wrote:
> > >On Sep 2, 2:40pm, Fernando Mato Mira wrote:
> > >> Subject: Re: GIS
> > >
> > >> But the point is, can we expect ClipTexture support for Linux? If so,
> when?
> > >
> > >This is a perfect question to send to Mongoose-feedback!
> >
> > OK. I'll do that.
> >
> > >As Angus explained, cliptexture requires special hardware. But there are
> >
> > I've always been curious regarding what that hardware is precisely (where
> > it is, how it integrates with IRIX, etc.)
>
> The easiest way to think about this is that a cliptexture is a virtual
> texture with maximum dimensions of 2^31 by 2^31. All your geometry
> has s & t texture coordinates into this single virtual texture. Performer
> is responsible for moving pieces of your clipmap database in and out
> of the texture cache and updating the clipcenter so that you will
> have the highest resolution available for geometry in your view.
>
> What do you mean by "where it is"? Infinite Reality graphics are
> the only place you will find cliptextures today.
>
> All access to this special hardware is through OpenGL extensions, many
> of which we don't give out any details on.

We do document the SGIX_clipmap extensions, it's actually pretty
straightforward and is described in glTexParameterf.

>... Our design goal was to
> enable the hardware through IRIS Performer. You would be very hard
> pressed to get any cliptexture to work outside of IRIS Performer. But
> it is possible. I don't know of anybody who has ever tried though.

Exactly, you could do it, but you might preffer to poke your eyes out
with a sharp stick. Not because it's hidden, but it's hard. The load
ballancing asyncronous loading and memory & bandwidth management (system
and texture) is already there in Performer.

Cheers,Angus.

-- 
"One of the best-known folk theorems of software engineering is that
60% to 75% of conventional software projects are either never
completed or rejected by their intended users. If that range is
anywhere near true (and I've never met a manager of any experience
who disputes it) then more projects than not are being aimed at goals
which are either (a) not realistically attainable, or (b) just plain
wrong."
                 Eric S. Raymond - The Cathedral and The Bazaar


For advanced 3D graphics Performer + OpenGL based examples and tutors:
http://www.dorbie.com/

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