Physical screen size for the X window system

Introduction

It's not particularly easy to get the physical screen size in millimeters (or centimeters, inches, however you want to convert it) in the X window system. Using the command line, it's possible to use xrandr | grep ' connected', which might produce output like

eDP-1-1 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 309mm x 173mm
HDMI-1-1 disconnected (normal left inverted right x axis y axis)
DP-1-1 disconnected (normal left inverted right x axis y axis)
HDMI-1-2 disconnected (normal left inverted right x axis y axis)

for my FullHD laptop with 309mm × 173mm resulting in a diagonal measurement of about 14 inches.

But: this only works on the command line. If you'd like to get this information from a native C++ Linux application, you're in trouble. I ran into the same problem, and of course calling shell commands is evil, thus I created this library.

It is based on GitHub user raboof's xrandr project. You can find the license for it here. I extracted the parts responsible for fetching the screen sizes and put them into C++ classes to make using them easier and more intuitive.

Requirements

• a Linux OS using the X window system
• g++ supporting at least C++11
• installed development files for X11 and Xrandr

Usage

The only file for you to include is XScreenSize.hpp. It defines the XScreenSize namespace. Looking at the short piece of demo code in main.cpp, you can see that it's enough to produce output like this:

screen 0: 1920px x 1080px
    eDP-1-1 [connected] at 60.0079Hz: 1920x1080+0+0, 309mm x 173mm
    HDMI-1-1 [disconnected]
    DP-1-1 [disconnected]
    HDMI-1-2 [disconnected]

• XScreenSize::XrandrOutput contains the members name, connection, has_details, refresh, x, y, width, height, mmWidth and mmHeight which should be self-explanatory when looking at the sample output above; only when has_details is true, the members following it are well-defined
• note that the internal code for getting all of this information is kept in the constructor of XScreenSize::Getter, so right after creating an instance, you can refer to its outputs
• the constructor will throw an std::runtime_error in case of an error, so make sure to catch it if needed
• if you'd like to use a different X display or a different screen, pass them to the constructor in that order

To build and run the demo file, run make, followed by bin/x-physical-screen-size.