Re: linking a slim liboctave without OpenGL or Nvidia stuff

[Andreas Weber]

Hi Daniel, sorry for the late answer

Am 22.12.2017 um 11:30 schrieb Daniel J Sebald:
> On 12/21/2017 11:48 PM, Andreas Weber wrote:
>> Dear all,
>>
>> is it feasible to compile and link a separate slim liboctave without
>> OpenGL and other stuff which might influence libosmesa?
>> Just enough to hgload a figure and print it.
>>
>> My idea is to create a standalone helper program (lets call it oct_print
>> for now) which links osmesa but not the Nvidia or AMD libgl or other
>> non-mesa libs)
> 
> Andy, I looked at some osmesa-related stuff quite some time ago, so I
> have forgotten exactly how it interacts with the program, but doesn't
> osmesa need some type of non-mesa, OpenGL driver to function?

As far as I understand the OSMesa architecture it provides the same
symbols like libGL would do so linking agains libosmesad is sufficient.

> LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libGL.so make

I know we are using this trick and suggest it since OSMesa was added in
2015 especially for Nvidia users but I always thought it's a dirty
workaround. I don't think the speed penalty using this for the onscreen
OpenGL rendering with FLTK or Qt would be dramatically.

> Rather than build a whole new octave, maybe experiment with the ideas
> above to see if you can generate an off-screen plot without Nvidia.

As I've found out the last two days the check for a valid X11 display is
deeply anchored in Octave core, the gtk-manager, __init_fltk__ and so on
so that real offscreen printing on a headless server seems much more
unrealistic than I've thought before.

-- Andy