How to query X11 display resolution?

Question

It seems like an simple problem, but I can't find the answer: How do you query (via X11) what monitors exist and their resolutions?

Answer 1

Check out display macros and screen macros from the Xlib manual.

Specifically:

• From the first link: ScreenCount(), ScreenOfDisplay()
• From the second link: WidthOfScreen(), HeightOfScreen()

Answer 2

This might be helpfull for cli and scripting

xwininfo -root

But xRandR might be more accurate, especially, when there is multiple monitor environment:

xrandr

Answer 3

For modern X servers, there's also the XRandR extension, which provides the most up-to-date model of multi screen layout information, including overlapping screens and dynamic screen changes.

Documentation of it is available in the XRandR 1.3.1 Protocol spec and the libXrandr man page.

Answer 4

If Xinerama is in use, try XineramaQueryScreens. Otherwise, you may be able to assume a single screen and use (X)WidthOfScreen/(X)HeightOfScreen.

(Also see the other answer. It's remotely possible someone is using the old X screen model where your screens are :x.0, :x.1, etc.)

Answer 5

The library X11 working only with unix-like OS, so it is a not cross-platform solution.

A full code

#include <stdio.h>

#include <X11/Xlib.h>

int
main(const int argc, const char *argv[])
{

    Display *display;
    Screen *screen;

    // open a display
    display = XOpenDisplay(NULL);

    // return the number of available screens
    int count_screens = ScreenCount(display);

    printf("Total count screens: %d\n", count_screens);


    for (int i = 0; i < count_screens; ++i) {
        screen = ScreenOfDisplay(display, i);
        printf("\tScreen %d: %dX%d\n", i + 1, screen->width, screen->height);
    }

    // close the display
    XCloseDisplay(display);

   return 0;
}

A compilation

gcc -o setup setup.c -std=c11 `pkg-config --cflags --libs x11`

A result (actual for my computer)

Total count screens: 1
    Screen 1: 1366X768

Based on:

1. https://tronche.com/gui/x/xlib/display/opening.html
2. https://tronche.com/gui/x/xlib/display/display-macros.html
3. https://tronche.com/gui/x/xlib/display/screen-information.html
4. https://stackoverflow.com/a/1829747/6003870

Answer 6

Clean xrandr output for imagemagick use

xrandr |grep \* |awk '{print $1}'

Answer 7

Python

import os
from Xlib import X, display
d = display.Display()
s = d.screen().root
output = os.popen("xrandr --listmonitors | grep '*' | awk {'print $4'}").read().splitlines()
num_sc = s.xinerama_get_screen_count().screen_count
width = s.get_geometry().width
height = s.get_geometry().height
print("Total count screens: %s" % num_sc)
for i in range(num_sc):
    print("\tScreen %s(%s): %sX%s" % (i, output[i], width, height))

Bash

$ xrandr --listmonitors
$ xrandr
$ xrandr | grep '*' | awk {'print $1'}