split GL image in 4 horizontal bands

    Mar 20 2006 | 1:22 pm
    Hi everybody,
    Does anyone have any experience with or ideas for splitting 1 openGL context in 4 horizontal bands, where each of those bands is sent to a different beamer ? Before I start researching intensively, I'm wondering whether it is even possible... ?

    • Apr 07 2006 | 2:59 pm
      Ok... made a little test patch to see how to distribute the image made by 1 jit.gl.sketch object to 4 different matrices, with the intention of ultimately sending each of those 4 parts to a different screen. Alternative approaches to do this are much appreciated...
      rgrds, b.
    • Apr 07 2006 | 3:56 pm
      I use Open Sound Control to send the openGL commands to 'n' separate machines. I use the 'lookat' message to jit.gl.render to shift the cameras view to 'line up' the screens. each camera is at the origin, but since im 'rotating' them, each 'screen' (or output device) ought to be rotated to maintain proper perspective and convincing illusion of seamlessness.
      its a bit trickier if you want to change your lens angle on the fly. I havent quite gotten that forumla down, but I did reverse engineer a second order polynomial from manually finding points that line up, plotting them, and then solving for the equation. It .. basically works.
      here is a set of patches that work together to have '2' screens (left and right), 2 render contexts and one controller. no OSC, just a rough outline of my method. Note this is an attachment, so I dont know if the forum will deal with it properly. open up left and right first, then controller. controller has a pwindow with a jit.gl.handle associated that moves, rotates etc the objects in both windows. play with the lens angle too. it ought to startup at 45
      also, id love someone to point out the 'right' way to calculate the lens-angle/lookat formula. Obviously it will involve some trig, but I havent really given it much thought.
      hope this helps:  v a d e //
      www.vade.info abstrakt.vade.info
    • Apr 07 2006 | 4:17 pm
      Forum seems to not handle the attachment well... but mail does ;) The d2r object is where you do the lookat offset calculation right?
      I'll have a look at your approach, since mine is also a bit intensive... having for synched computers would be great, but I'm afraid budgetwise that'll be a problem... I was thinking of a single quad g5 with a nvidia quadro nvs 440 or an ati firemv... but then the problem will be one of speed.. I want to render a kind of particle system using javascript which will also be difficult to distribute I suspect? A lot of new stuff to learn either way.
      more later!
    • Apr 07 2006 | 4:31 pm
      d2r is a degree to radians conversion object, which is from Jasch's objects.
      since you are rendering separate contexts, there is no penalty for 'screen stretching' to a different card (ie reading back from one card to another), so with a nice card, (or two.. two contexts on each card), I bet a quad could do something quite nice..
    • Apr 07 2006 | 7:00 pm
      you might want to look at new matrox multiscreen gadget that has one vga in, and 2 or 3 vga outs. It pretends to be single 2x or 3x ultrawide screen, so you could render single, triple width GL screen, and the box wold than split it to 3 discreet VGA outputs.
      It is not too expensive. Search the archives for matrox to get more info, as it was discussed recently.
    • Apr 08 2006 | 4:15 pm
      The matrox triplehead2go is indeed a nice thing.
      They also have the EXTIO F1400 (www.matrox.com/graphics/extio) now which supports 4 displays, but it's not even deliverable yet. I also came accross this funky gizmo : www.vistasystems.net/spyder.html which is very expensive :)
      The intention is to project on a cyllinder, so in the end I don't really need the horizontal resolution of 4 screens. I figured 1 time 1600x1200 should do, with each beamer displaying a fourth (400x1200). So a messy way of doing this is : 1 output, vga splitter, and manually masking the beamers. Since this is to much of a hastle to set up, I was hoping there would be a way to have 4 outputs with the same content of which 3/4'ths of the image is masked in openGL (like in the letterbox example a few posts back). Even better would be to be able to take a fourth of the image, and place it in the center of a new 1600x1200 screen (because otherwise it would also require to offset the beamers depending on which part of the image they show)
    • Apr 12 2006 | 6:00 pm
      FYI I just found out that the Triplehead2go won't be out until May. $299 MSRP. Can't beat that! In the meantime, I just ordered the Dualhead2go, to try it out (only $150)
    • Apr 12 2006 | 7:24 pm
      I just saw the Matrox Qid Pro, 4 outputs... costs minimum 835$ though... (guess you don't get something for nothing, har har)
    • Apr 12 2006 | 8:28 pm
      is it openGL accelerated
      v a d e //
      www.vade.info abstrakt.vade.info
      You will not be saved by the Holy Ghost. You will not be saved by the God Plutonium.
      In fact, YOU WILL NOT BE SAVED!
    • Apr 12 2006 | 8:54 pm
      they say : full opengl acceleration... but how and what is always a matter of testing I guess... 256Mb onboard memory... but that doesn't sound like much if you drive 4 monitors with 1600x1200 resolution.