Re: Benefits of Display listing of geosets
Guy Russell (guyr++at++thoth.engr.sgi.com)
Thu, 19 Sep 1996 15:57:47 -0700
On Sep 16, 6:07pm, Michael T. Jones wrote:
> Subject: Re: Benefits of Display listing of geosets
> On Sep 16, 12:43pm, Ken Sakai wrote:
> > Subject: Benefits of Display listing of geosets
> >
> > Perfomers,
> >
> > Does anyone have an idea of how much of a performance increase
> > pfGSetDrawMode(geoset, PFGS_COMPILE_GL, val) will tend to buy you
> > on the various platforms? I know that objects drawn using OpenGL
> > display lists display MUCH faster than those drawn in immediate mode
> > in iR's. Will OpenGL display lists buy you much on Impact graphics,
> > RE graphics, and on Extreme graphics systems? I was told that
> > OpenGL display lists should also run faster on Impact machines but I do not
> > seem to be getting any speed increase with
> > pfGSetDrawMode(geoset, PFGS_COMPILE_GL, val) on Impacts.
>
> Performer's immediate-mode rendering has always been as fast or
> faster (usually faster) than IRIS GL or OpenGL display-list mode.
> This is true on iR also, but there's more to the story...
>
> ...InfiniteReality has a 15+ megabyte cache on the geometry engine
> board that is used to keep local copies of certain display lists.
> Not all display lists can be kept locally (i.e., those that do
> texture binds prevent lists from being cached). For those that are
> in fact able to be cached, the difference between cached display
> list and immediate mode over the Onyx-to-iR bus is significant and
> will almost always result in better performance. This is due to
> the cache's greater bandwidth than the bus interface.
>
> For this reason, we made the perfly in Performer 2.1 default to the
> display-list mode. To see the difference, use the "d" (for display
> list) and "i" (for immediate mode) keys to toggle between the two
> cases.
>
> On other machines there is not the same advantage for display lists
> that you'll see on iR. In the future, should bus speeds increase,
> we'll see the advantage of display list mode decrease, perhaps to
> the point where it won't be used.
It is true that other machines do not have display list memory in hardware,
however display lists are still a potential performance win on the Impact. If
a display list is pullable, the graphics will initiate the DMA for the display
list from main memory. Pullability keeps the processor from getting involved
in the I/O for the display list. On a single processor system this can be a
big win if you are CPU limited. Most vis sim oriented display lists will be
pullable. The one major exception to date is anytime a display list binds a
texture. This limitation will be removed in upcoming releases, but for now you
must keep bind texture calls out of pullable display lists.
>
> Michael
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>-- End of excerpt from Michael T. Jones
Guy
--
Guy Russell
Vis Sim Applied Engineering Silicon Graphics Inc.
Email:guyr++at++engr.sgi.com 2011 N. Shoreline Blvd. M/S 3L-916
Phone:(415)933-6113 Mountain View CA 94043
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