c++linuxframe-ratexorg

C++ Linux: Get the refresh rate of a monitor

In Windows, winapi provides a function that reports information about a monitor:

DEVMODE dm;
dm.dmSize = sizeof(DEVMODE);

EnumDisplaySettings(NULL, ENUM_CURRENT_SETTINGS, &dm);

int FPS = dm.dmDisplayFrequency;

What is the equivalent of this on Linux? The Linux man pages direct me to an allegro library function, but not only am I not using allegro, that function is from a very outdated version of said library and reportedly only works on Windows.

Solution

  • Use XRandr API (man 3 Xrandr). See here for an example:

    You can also look at the code for xrandr(1).

    Edit1: For posterity sake:

    Sample code slightly adjusted so its more of a demo:

    #include <cstdio>
#include <cstdlib>
#include <cstring>
#include <string>
#include <iostream>
#include <unistd.h>
#include <X11/Xlib.h>
#include <X11/extensions/Xrandr.h>

int main()
{
    int num_sizes;
    Rotation current_rotation;

    Display *dpy = XOpenDisplay(NULL);
    Window root = RootWindow(dpy, 0);
    XRRScreenSize *xrrs = XRRSizes(dpy, 0, &num_sizes);
    //
    //     GET CURRENT RESOLUTION AND FREQUENCY
    //
    XRRScreenConfiguration *conf = XRRGetScreenInfo(dpy, root);
    short current_rate = XRRConfigCurrentRate(conf);
    SizeID current_size_id = XRRConfigCurrentConfiguration(conf, &current_rotation);

    int current_width = xrrs[current_size_id].width;
    int current_height = xrrs[current_size_id].height;
    std::cout << "current_rate = " << current_rate << std::endl;
    std::cout << "current_width = " << current_width << std::endl;
    std::cout << "current_height = " << current_height << std::endl;

    XCloseDisplay(dpy);
}

    Compile with:

    g++ 17797636.cpp -o 17797636 -lX11 -lXrandr

    Output:

    $ ./17797636 
current_rate = 50
current_width = 1920
current_height = 1080