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

Question

I would like to display images in the second monitor. I have two displays of 1920x1080px connected and detected properly in Ubuntu.

I am listing the screens with the following code. The problem is that I am listing always just one screen0: 1920x1080 for a single display configuration and a 3840x1080 for a multiple display (exended or duplicated).

How can I get the list of two displays in order to select just screen1 (second display 1920x1080)?

Display *myDisplay = XOpenDisplay(NULL);

unsigned int numScreens = ScreenCount(myDisplay);

for(unsigned int i=0; i<numScreens; i++){

    Screen *myScreen = ScreenOfDisplay(myDisplay, i);
    ScreenInfo screen;
    screen.resX = myScreen->width;
    screen.resY = myScreen->height;
    char screenName[50];
    sprintf(screenName, "Screen number %d", i);
    screen.name = screenName;

}

update: here is my xrandr output, that shows the two displays properly connected, and I can use it accordingly. However, if I access to the available displays, I can get only :0 with one screen with 3840x1080. How to get two displays (:0 and :1)?

vo@vo-ubuntu:~$ xrandr
Screen 0: minimum 320 x 200, current 1920 x 1080, maximum 8192 x 8192
HDMI-1 connected 1920x1080+0+0 (normal left inverted right x axis y axis) 527mm x 296mm
   1920x1080     60.00*+  60.00    50.00    50.00    59.94  
   1920x1080i    60.00    60.00    50.00    59.94  
   1600x1200     60.00  
   1680x1050     59.88  
   1400x1050     59.95  
   1600x900      60.00  
   1280x1024     75.02    60.02  
   1440x900      59.90  
   1280x960      60.00  
   1152x864      75.00  
   1280x720      60.00    60.00    50.00    59.94  
   1024x768      75.03    70.07    60.00  
   832x624       74.55  
   800x600       72.19    75.00    60.32    56.25  
   720x576       50.00    50.00  
   720x576i      50.00    50.00  
   720x480       60.00    60.00    59.94    59.94    59.94  
   720x480i      60.00    60.00    59.94    59.94  
   640x480       75.00    72.81    66.67    60.00    59.94    59.94  
   720x400       70.08  
HDMI-2 disconnected (normal left inverted right x axis y axis)
DP-1 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 527mm x 296mm
   1920x1080     60.00*+
   1600x1200     60.00  
   1680x1050     59.95  
   1400x1050     59.98  
   1600x900      60.00  
   1280x1024     75.02    60.02  
   1440x900      59.89  
   1280x960      60.00  
   1152x864      75.00  
   1280x720      60.00  
   1024x768      75.03    70.07    60.00  
   832x624       74.55  
   800x600       72.19    75.00    60.32    56.25  
   640x480       75.00    72.81    66.67    59.94  
   720x400       70.08  
DVI-D-1-1 disconnected (normal left inverted right x axis y axis)
HDMI-1-3 disconnected (normal left inverted right x axis y axis)
DP-1-2 disconnected (normal left inverted right x axis y axis)

Check available X displays doesn't return the two connected displays,

vo@vo-ubuntu:~$ cd /tmp/.X11-unix && for x in X*; do echo ":${x#X}"; done
:0
:1024
vo@vo-ubuntu:/tmp/.X11-unix$ 

Answer 1

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