Xlib: capture screen in separate xserver session

[Ilya Anfimov]

On Tue, Feb 07, 2017 at 09:47:43PM +0300, Alex Sviridov wrote:
>    Hi all.
> 
>    I need to run some-program which makes screen capturing via xlib library
>    in separate xserver session. So, I start my ubuntu 14 and `origin` xserver
>    session (lets call it this way) starts. After that I run
> 
>        startx some-program

[skipped]

>    xserver session while it is not active (the user is using another
>    xsession).

  Using  it  this  way  is nearly impossible: for some historical
reasons, inactive server stops drawing. Well, not  just  histori-
cal:  it  is  a  reasinable approach to stop wasting resources to
draw unseen things.

 However, you can start virtual X server  (like  standard  Xvfb),
and draw on it just fine.
 You  can  even  try  to work interactively with programs on that
server via something like x2x or  x11vnc  or  x2godesktopsharing,
however,  usually  interactive experience is worse than with con-
sole server.
 Also, no hardware 3D acceleration will  be  available.  It  also
works  only  on active console currently. If you need it, you can
try to use some server-in-window servers like xpra,  however,  it
is  not  perfect (and all attempts to implement it in the past --
Xgl, AIGLX was not perfect also).