Programmatically Determining Individual Screen Widths/Heights in Linux (W/Xinerama, Twinview, And/Or Bigdesktop)

Programmatically determining individual screen widths/heights in Linux (w/Xinerama, TwinView, and/or BigDesktop)

It looks like there's a libXinerama API that can retrieve that information. I haven't found any detailed information on it yet though.

General X.org programming information can be found here (PDF file). Information on the functions provided by libXinerama can be found here (online copy of a manpage, not a lot of information in it).

Here's a small C++ program that I whipped up from those references to retrieve the dimensions and offsets of each of the monitors hooked into Xinerama. It also works for nVidia TwinView; I don't presently have an ATI card to test it on their BigDesktop system, but I suspect it would work on it as well.

#include <cstdlib>
#include <iostream>

#include <X11/extensions/Xinerama.h>

using std::cout;
using std::endl;

int main(int argc, char *argv[]) {
    bool success=false;
    Display *d=XOpenDisplay(NULL);
    if (d) {
        int dummy1, dummy2;
        if (XineramaQueryExtension(d, &dummy1, &dummy2)) {
            if (XineramaIsActive(d)) {
                int heads=0;
                XineramaScreenInfo *p=XineramaQueryScreens(d, &heads);
                if (heads>0) {
                    for (int x=0; x<heads; ++x)
                        cout << "Head " << x+1 << " of " << heads << ": " <<
                            p[x].width << "x" << p[x].height << " at " <<
                            p[x].x_org << "," << p[x].y_org << endl;
                    success=true;
                } else cout << "XineramaQueryScreens says there aren't any" << endl;
                XFree(p);
            } else cout << "Xinerama not active" << endl;
        } else cout << "No Xinerama extension" << endl;
        XCloseDisplay(d);
    } else cout << "Can't open display" << endl;

    return (success ? EXIT_SUCCESS : EXIT_FAILURE);
}

C++ list screens to display images in the second monitor

It's likely that you need to query Xinerama, which is probably stitching your displays together.

This answer worked for me. I compiled their sample with:

g++ xinerama.c `pkg-config --cflags --libs x11 xinerama` -o test

gdk_screen_get_default() returns null

Answering my own question.

Finally, figured out the resolution. gtk_init( ) was missing before fetching the screen. Added that and respective include for gtk/gtk.h and now the code looks like

int main(int argc, char *argv[]) 
{ 
   gtk_init(&argc, &argv);                 // <---- added this

   GdkScreen *screen = gdk_screen_get_default(); 

   : 
   followed by rest of the code shared in the problem description above. 

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