Angus Dorbie (dorbie++at++sgi.com)
Mon, 30 Aug 1999 16:57:26 -0700
Clip texture is interesting because it solves problems of MIP level
management and texture id juggling, which seem to supply
disproportionate levels of grief when it comes to actually implementing
these schemes, particularly in a multiprocess environment. The
capabilities of the ONYX2 infinite Reality hardware extend beyond these
benefits.
It's worth bearing in mind that these geospecific requirements are
fundamentally bandwidth problems, not frame rate although you need both
simultaneously. In some sense, you can either do it or you can't
irrespective of frame rate, although you may be able to get more paging
time by limiting other graphics load. You can either sustain the data
rates required for a given swath of certain ground resolution and
velocity or you can't. Dropping the frame rate won't necessarily make it
possible, only dropping terrain resolution or eye velocity will help.
There are also system level requirements which I would say are extremely
difficult to sustain reliably on a PC with Win32 operating systems. With
large CLIP texture class databases you cannot hold them in system
memory, so the approach has to be one of sustaining high bandwidth i/o
from disk to system memory while paging from system memory to the
graphics pipe, while performing application processing culling and
rendering. That requires asynchronous data management linked to fine
grained real-time texture memory updates from the draw process. All with
graphics at a steady 60 Hz.
It seems more than a little optimistic to say a PC can just do this.
Sure it can do something but it can't handle the same class of problem.
You have to compare apples with apples, doing otherwise is exactly the
kind of loosely defined approach to analysis which has led to problems
of programs like CCTT where they realized too late that PC's weren't
going to do the job.
Cheers,Angus.
Steve Gifford wrote:
>
> At 11:37 AM 8/30/99 +0200, Fernando Mato Mira wrote:
> >Are there any (upcoming) low-cost platforms supporting geospecific
> >texturing (ClipTextures)?
>
> Any decent OpenGL, Glide, or DirectX based graphics card with an adequate
> amount of texture memory can handle a geospecific textured database. It
> just needs to be structured correctly. In particular, not as one giant
> texture.
>
> Cliptexture is just one solution for geospecific textured databases, a very
> good one mind you, but just one of many.
>
> So the answer to your question is (was) yes. This happened at least a year
> ago.
> Just to keep this a little more relevant to Performer, paging individual
> smaller textures is what you typically have to do on non-IR systems, such
> as the Impact or O2 systems.
>
> -Steve Gifford
> TERREX Inc.
>
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