FYI I just went through this w/ an application of ours. There is no easy way
to handle this. You can do this:
Display* disp = XOpenDisplay( 0 );
if ( ! disp )
{
// no DISPLAY variable is set - no x connection
}
However, if the DISPLAY variable is set but doesn't point to a usable x-server
(or it can't connect to the x-server), this will actually call halt/exit inside
the X library. The X library has this coded as the standard error behavior.
You can set a custom X11 IO error handler but it's kind of worthless because if
the error handler ever returns, the X11 library will exit. The work around is
to do a setjmp/longjump call in the error handler.
Here's the resulting code we use to check for a valid x-server connection. We
actually trap 3 different conditions (success, no display, display but can't
connect). You modify this a little bit if you just wanted to check for a valid
display.
====================================
#include <X11/Xlib.h>
#include <setjmp.h>
static jmp_buf s_displayJumpBuf;
static int s_xIOhandler( Display* disp )
{
// Jump back to the status function.
longjmp( s_displayJumpBuf, 1 );
return 0;
}
int serverStatus()
{
typedef int (*ErrorHandler)( Display* display );
// Initial execution path. setjmp() returns 0 to begin with. If
// XOpenDisplay fails and calls the error handler, then execution
// will resume here but with a non-zero return value.
if ( setjmp( s_displayJumpBuf ) == 0 )
{
// Set our handler and try to open the display.
ErrorHandler prevHandler = XSetIOErrorHandler( s_xIOhandler );
Display* disp = XOpenDisplay( 0 );
// Restore the previous handler.
XSetIOErrorHandler( prevHandler );
// Success - valid X11 display.
if ( disp )
{
return 0;
}
// DISPLAY env variable not set.
return -1;
}
else
{
// X11 IO error indicates that a DISPLAY variable was set but
// that it's invalid.
return -2;
}
}
> -----Original Message-----
> From: Christopher Barker [mailto:chris.bar...@noaa.gov]
> Sent: Monday, June 01, 2009 11:45 AM
> To: matplotlib-users@lists.sourceforge.net
> Subject: Re: [Matplotlib-users] Non-X11 fallback on import
>
> Alexander Lamaison wrote:
> > I would like it to work
> > is to use the default backend if X is available and, otherwise, fall
> > back to using the Agg backend. How can I do this?
>
> I had a similar need a good while back with wxPython. I found some C
> code on the net that tries to connect to an X server and fails
> gracefully if it can't. I also wrote a Python wrapper around it. I
> haven't used it for years, and can't even find it on my machine, but
> thanks to the glory of archives and google, here it is:
>
> http://osdir.com/ml/python.wxpython/2004-03/msg00294.html
>
> You'd use it like:
>
> import matplotlib
> import isX
>
> if isX.isX:
> matplotlib.use("wxGTK") or whatever..
> else:
> matplotlib.use("AGG")
>
>
> note that you can also just check and see if the "DISPLAY" environment
> variable is set, but that won't be as reliable.
>
> However, as the whole user interaction has to be totally different, I
> wonder if you can't just have a different start-up script depending on
> whether they want to run the GUI version or not.
>
>
> -Chris
>
>
>
>
> --
> Christopher Barker, Ph.D.
> Oceanographer
>
> Emergency Response Division
> NOAA/NOS/OR&R (206) 526-6959 voice
> 7600 Sand Point Way NE (206) 526-6329 fax
> Seattle, WA 98115 (206) 526-6317 main reception
>
> chris.bar...@noaa.gov
>
> -----------------------------------------------------------------------
> -------
> Register Now for Creativity and Technology (CaT), June 3rd, NYC. CaT
> is a gathering of tech-side developers & brand creativity
> professionals. Meet
> the minds behind Google Creative Lab, Visual Complexity, Processing, &
> iPhoneDevCamp as they present alongside digital heavyweights like
> Barbarian
> Group, R/GA, & Big Spaceship. http://p.sf.net/sfu/creativitycat-com
> _______________________________________________
> Matplotlib-users mailing list
> Matplotlib-users@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/matplotlib-users
------------------------------------------------------------------------------
OpenSolaris 2009.06 is a cutting edge operating system for enterprises
looking to deploy the next generation of Solaris that includes the latest
innovations from Sun and the OpenSource community. Download a copy and
enjoy capabilities such as Networking, Storage and Virtualization.
Go to: http://p.sf.net/sfu/opensolaris-get
_______________________________________________
Matplotlib-users mailing list
Matplotlib-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/matplotlib-users
