GL over remote X ;was Re: [lug] good assert library

[Chan Kar Heng]

>>anyway, would you know what gets sent across network in
>>the case where machine A runs an X opengl program that
>>resides on machine B? (remote X)...
>
>I believe there is an OpenGL intercept/proxy library that can be used to catch OpenGL calls and log them, sort of like ltrace or strace for normal library or system calls. What I don't know is if any of these are available under Linux, I know there are several under Win32. Some names for Win32 side, which might or might not have a Linux version:
> Chromium, glTrace, HijackGL, GPT, ZapDB
>
>(and even if they do have Linux versions, they might not be what you want, and they might fail under remote X11)
>
>You might be more interested in using a network sniffing tool on the X11 port. There is a possibility that if compression is being used over the network, you could find the right arguments to make X11 *not* compress, to aid debugging.

didn't know there were existing GL interceptors/proxy libraries around..
thanks for the info! :)
but i suspected there'd be some kind of this library within the GL implementation
for X too.. hmm..

btw, i'd probably have to use telnet instead of ssh for the X connection
to use a net sniff tool.. :)

perhaps i'd just see if i could check it out from the X mailing list or Mesa
mailing list or from parts of the X or Mesa sources... hmm.


>>either arguments of opengl function calls get sent or the
>>rendered images on the window get compressed and sent.
>>i'm wondering which... or maybe it works another way?
>
>I couldn't answer that, you are at the driver level there, for both OpenGL and X11. X11 tends to have a surrogate copy of state on both machines, and what it actually sends depends on what calls are made; some information seeking requests will cause flushing of buffers and lower performance, whereas otherwise it can be allowed to throw out some values from unused events, if a series of events do not require the intermediate events. I doubt it matters that OpenGL is involved, except that there might be an X extension involved. Mostly I would say it is up to X protocols.

gee... copies of state on both machines??
hmm!
anyway, somehow i've got a feeling that there's a specific version
for X... will check it out... and if i find out, i'll post some info here on
the list.. :)



>Knowing more about what you want to accomplish could help. The most common failure I've seen from just playing with it is that sometimes people try to use the X Shared Memory mechanism, and do not offer a way to turn it off...there is an underlying assumption in such code that the app is always running and displaying on the same machine (not a bad assumption if it is Win32 or Mac code that got ported to Linux/X11).

well, actually was toying with the idea of a client server s/w that
renders across network... havn't really thought of the specific area
of application yet..

heavy implementation on server side, thin implementation on client
side...
the server would probably need several contexts for each client
connection or group session...

anyway, i played around with GL remote X to test out feasibility...
i still get fairly good speed at 19.2Kbps with a ssh remote X connection.
so i was just wondering how it was done.. :)


rgds,

kh