[PD] many DVI ports with Debian/Ubuntu and Gem

IOhannes m zmoelnig zmoelnig at iem.at
Mon Jun 7 09:49:16 CEST 2010

On 2010-06-03 19:23, Hans-Christoph Steiner wrote:
> I am looking into doing a 10 screen installation using Pd/Gem.  I'd like
> to run it on as few computers as possible.  Anyone have any
> recommendations for Debian or Ubuntu setups that can have like many DVI
> ports in one computer?

the biggest thing i did with something like this was an 8 projector
installation [1], using a single computer (running ubuntu; i would have
preferred debian, but some software we had to license was only available
for ubuntu)) with 2 "recent" nVidia cards (forgot which ones; it was
done last year, so probably it was 2 GTX295 or similar);
3 heads where equipped with triplehead2go, which would have made for a
total of 9 projectors, but we only needed 8; the remaining head was the
control computer to do the patching.

there were 2 problems involved (and solved):
- getting the gfx-card recognize the 3head2go over shitty cables (which
we ended up solving by forcing EDIDs)
- window size:
depending on your hardware/driver combination, you get a maximum texture
size. with the cards we used this texture size was 8192x8192.
this size (both horizontal and vertical) is an upper boundary for
hardware-accelerated window sizes. so you cannot do a line of 8
projectors in a row, each with a resolution of 1080p, as this would sum
up to a window of (8*1920)x1080==15360x1920, and 15360 clearly being >8192.
what you can do is to have your line of 8 screens form a virtual monitor
of 4x2 screens, covered by a 7680x2160 window and use framebuffers for
rendering the scene (this really only matters if there is continuation
between the screens (e.g. in our project we actually had one huge 270°
screen, which was fed by 8 projectors)
if the screens are more or less independent, then it's way simpler)



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