View Full Version : Accessing existing buffers (X-windows)

Alex Cope
11-12-2007, 01:09 PM

I figured since I am a beginner this question belongs here, although the subject matter is a little more advanced.

Basically what I wish to do is access the OpenGL output of a program under X and stream it out over a network in a form I choose. Basically what Yukon (http://www.neopsis.com/projects/yukon/) does, but with no audio and for a program with two OpenGL windows (only one of which I wish to copy).

The desired method would be to obtain the handle of the correct window - automatically or otherwise - and use this to access the buffer using GLX and then glReadPixels(). Since Yukon seems to do this by subsuming parts of the GL library am I correct in assuming this cannot be done? Or are they just being more clever than I need to be (this need only work in a very controlled environment for me)?

So the real questions here are:
1. Will this method work & if so how (a rough outline will be enough to get me started - I can figure out specifics)?
2. Can this be achieved any other way?
3. Is this the wrong BB for such OS specific queries - if so can you point me in the right direction.


11-12-2007, 02:55 PM
You are in a very controlled environment but you can't recompile the program you want to video grab ? What program is it ?

I guess the best way to do it is to grab the Yukon sources, see how they do it, fiddle until you can grab the second window.

Dark Photon
11-19-2007, 07:22 AM
what I wish to do is access the OpenGL output of a program under X and stream it out over a network in a form I choose.
Operative question is whether you just want to relay the color buffer at some rate (what I'm assuming), or whether you want to reproduce the depth/multisample, and others as well, possibly with some sort of modification/playback of the GL event stream. Without more constraints, the former suggests maybe a simple xv/ksnapshot-style read the color buffer approach possibly with some simple real-time video compress, while the latter might suggest tapping into GLX stream ala Chromium.

For the former, I agree with ZbuffeR. If Yukon seems too tough, try ksnapshot, xv, or any one of a number of other sources to see how to grab the color buffer. As long as you have read access to the X display, you can pretty much do what you want.

(In all this, I'm assuming you don't just want to run app on machine #1 and display on machine #2. That's easy presuming similar X/GLX capabilities and app not presuming a direct rendering context.)

Would suggest follow-ups to the GLX forum, ...but I see we don't have one. So perhaps this is the best place.