On 12/22/11 10:01 AM, Stefan Eilemann wrote:
>> If you need to know of VGL's existence prior to that, you'd have to look
>> at the value of the LD_PRELOAD environment variable and see if it
>> contains "librrfaker.so". [...]
>
> That sounds like what I want - thanks!
Well, just be aware that it isn't reliable.
>> Maybe if I understood what "doVglSpecificStuff()" is, I could give you a
>> more solid answer. I'm not sure why an application would want to change
>> up the way it renders because VirtualGL is present.
>
> Setup is a 3-GPU 'VGL-served' machine. With VGL present, I want:
>
> - two offscreen renderers using :0.1 and :0.2 contributing to:
> - one on-screen renderer rendering and assembling :0.1 and :0.2 using the
> forwarded DISPLAY (:10.0, redirected to :0.0 by VGL)
>
> without VGL I want:
>
> - three off-screen renders using :0.0-:0.2 contributing to:
> - one on-screen renderer only assembling :0.0-:0.2, shipped by X11/indirect
> glX
>
> Basically the VGL config saves one pixel readback/assemble. Using the non-VGL
> config with VGL works too, but is suboptimal.
Why not just have your application putenv("VGL_READBACK=0")? That
prevents VirtualGL from reading back and sending frames, if you have
other means of doing that. You could, for instance, wrap a
glXSwapBuffers() call around which you don't want VirtualGL to do readback:
char *env=getenv("VGL_READBACK");
char string[256];
glXSwapBuffers(...);
if(env && strlen(env)>0) snprintf(string, 256, "VGL_READBACK=%s", env);
putenv(string);
This is a common technique when using VirtualGL with Chromium and
ParaView, although in those cases, the rendering is split up among
multiple processes, so VGL_READBACK=0 is set in the launch scripts for
the sub-renderers rather than being set in the main application, but the
principle is the same.
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