Re: Pipes
Angus Dorbie (dorbie++at++sgi.com)
Tue, 28 Jul 1998 11:21:07 -0700
Steve Baker wrote:
>
> On Tue, 28 Jul 1998, Mike Caruso wrote:
>
> > I'm relatively new to Performer and I have been reading the
> > documentation that came with it and it wasn't clear to me if it is
> > possible to use two or more Pipes to render to the same frame buffer. I
> > also got the understanding (and correct me if I'm wrong) that the word
> > "Pipe" is used in place of "Graphics Hardware", so another words a Pipe
> > is a graphics board or "Raster manager" in the machine.
>
> The terminology is in a bit of a mess IMHO.
>
> PIPE: On the higher end machines like ONYX's and such, a PIPE is a physical
> chunk of hardware comprising one Geometry Engine board, either 1, 2 or 4
> Raster Managers, and a Display Generator. (And possibly some other
> bits and pieces too). One pipe can drive several video outputs on
> some hardware - there are also occasions when people have combined
> multiple PIPEs to render a single video output - but you need some
> special hardware to do that. Most programs are unaware of how many
> video outputs are displaying the output of the pipe.
> On lower-end machines like an O2, a pipe is just a graphics board.
>
> RASTER MANAGER: A board that plugs into a PIPE. All the raster managers
> installed in a particular pipe contribute pixels to the frame buffer
> for that PIPE in an interleaved fashion. If you ever have a raster
> manager fail (No! Surely not!) on a pipe that has more than one
> raster manager, you often get a bunch of vertical lines on the
> screen where those parts of the overall frame buffer that reside
> on that pipe are missing.
>
> pfPipe: A Cull process and a Draw process associated with an X-window -
> there can be multiple pfPipes associated with a PIPE - but each
> pfPipe renders to just one PIPE.
>
> CHANNEL: Depending on what documents you read, this can be a
> PIPE, a VIDEO OUTPUT, a pfPipe or a pfChannel - avoid this
> term!
>
> pfChannel: A rectangular portion of a pfPipe into which an image is
> (usually) rendered. There can be several pfChannels associated
> with a single pfPipe. There is not necessarily a direct relationship
> between a pfChannel and a video output - but this is often
> the case.
>
> > ...it wasn't clear to me if it is
> > possible to use two or more Pipes to render to the same frame buffer.
>
> Two or more PIPEs ... No.
> Two or more pfPipes ... Yes.
>
> > And since each raster manager has it's own hardware frame buffer...
>
> (Well, it's own share of the PIPE's frame buffer actually)
>
> > I was
> > wondering if it's possible to get two pipes to work together in rendering
> > a scene to one window with one channel in it.
>
> No - you can't have a 'window' (an X-window specifically) that straddles
> more than one PIPE (or more than one pfPipe for that matter). There have
> been cases where multiple PIPES have been used to drive a single video -
> IIRC, the Disney Aladdin ride did that at one time. It needs some special
> hardware though.
We have this for ONYX2 now, it was announced at Siggraph.
Reality Monster uses image readback to scale graphics for a single
channel across multiple pipes but you had to have an application which
could amortize the readback cost, typically this meant big CAD
databases or volume rendering, so for the right application the answer
has always been yes to the question, but not for vis sim. Now we have
a digital multiplexer option for the display generator board in the
pipe called "DPLEX". This supports a high bandwidth LVDS video
interconnect across pipes and lets multiple pipes render to a single
video stream. There is no readback overhead to amortize so it can
scale typical vis sim channels across to 2 or 3 pipes, beyond that
latency may be a problem depending on your requirements. If latency
isn't an issue then you can scale up to 16 pipes rendering to a
single video stream.
This was announced as part of the InfiniteReality2 product rollout,
which boosts InfiniteReality performance by up to 20% for geometry
transformation and anti-aliased fill, while adding support for up
to 16 pipes in a single system. There's an updated ONYX2 technical
report and some info should be on our web site soon.
Cheers,Angus.
--
"Only the mediocre are always at their best." -- Jean Giraudoux
For advanced 3D graphics Performer + OpenGL based examples and tutors:
http://www.dorbie.com/
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