X11 - Xrandr giving me false monitors

Question

I was trying to find all monitors and their coordinates (width w , height h , x origin/top-left-most x , and y origin/top-left-most y ) and was using this code, it works good on some systems. But on other systems I get false and duplicate entries. Would I be able to avoid these dupilcate/false monitor entries if I tested if monitor is mirror? How to test if its mirror?

So this is my code:

// start - get all monitor resolutions
var screen = XRRGetScreenResources(getXOpenDisplay(), getDefaultRootWindow(getXOpenDisplay()));

var noutputs = screen.noutput;

for (var i=noutputs-1; i>=0; i--) {
    var info = XRRGetOutputInfo(getXOpenDisplay(), screen, screen.outputs[i]);
    if (info.connection == RR_Connected) {
        var ncrtcs = info.ncrtc;
        for (var j=ncrtcs-1; j>=0; j--) {
            var crtc_info = XRRGetCrtcInfo(getXOpenDisplay(), screen, infoCrtcs[j]);
            console.info('screen #' + i + ' mon#' + j + ' details:', crtc_info.x, crtc_info.y, crtc_info.width, crtc_info.height);

            collMonInfos.push({
                x: crtc_info.x,
                y: crtc_info.y,
                w: crtc_info.width,
                h: crtc_info.height
            });

            XRRFreeCrtcInfo(crtc_info);
        }
    }
    XRRFreeOutputInfo(info);
}
XRRFreeScreenResources(screen);
console.info('JSON:', JSON.stringify(collMonInfos));
// end - get all monitor resolutions

And this outputs this to log:

"screen #4 mon#0 details:" 0 0 0 0
"screen #3 mon#1 details:" 0 0 1920 1200
"screen #3 mon#0 details:" 1920 469 1366 768
"screen #2 mon#1 details:" 0 0 1920 1200
"screen #2 mon#0 details:" 1920 469 1366 768
"screen #1 mon#1 details:" 0 0 1920 1200
"screen #1 mon#0 details:" 1920 469 1366 768
"screen #0 mon#1 details:" 0 0 1920 1200
"screen #0 mon#0 details:" 1920 469 1366 768

This is it in JSON format:

[{
    "x": 0,
    "y": 0,
    "w": 0,
    "h": 0
}, {
    "x": 0,
    "y": 0,
    "w": 1920,
    "h": 1200
}, {
    "x": 1920,
    "y": 469,
    "w": 1366,
    "h": 768
}, {
    "x": 0,
    "y": 0,
    "w": 1920,
    "h": 1200
}, {
    "x": 1920,
    "y": 469,
    "w": 1366,
    "h": 768
}, {
    "x": 0,
    "y": 0,
    "w": 1920,
    "h": 1200
}, {
    "x": 1920,
    "y": 469,
    "w": 1366,
    "h": 768
}, {
    "x": 0,
    "y": 0,
    "w": 1920,
    "h": 1200
}, {
    "x": 1920,
    "y": 469,
    "w": 1366,
    "h": 768
}]

I really only have 2 monitors, the 1920x1200 one and the 1366x768 one. How come all the other entries and how to test to avoid (rather then filter out in retrospect based on duplicates or 0 h/w)?

Answer 1

You are unnecessarily iterating over each output and then over each monitor . So you receive a duplicate entries. You do not have to call XRRGetOutputInfo for each output, since all data you need (number of monitors) can be found in structure returned by XRRGetScreenResources . Here is the C code that works (at least for me):

#include <stdio.h>
#include <stdlib.h>
#include <X11/Xlib.h>
#include <X11/extensions/Xrandr.h>

int main(void) {
    Display *d = XOpenDisplay(getenv("DISPLAY"));
    Window   w = DefaultRootWindow(d);
    XRRScreenResources *xrrr = XRRGetScreenResources(d, w);
    XRRCrtcInfo *xrrci;
    int i;
    int ncrtc = xrrr->ncrtc;
    for (i = 0; i < ncrtc; ++i) {
        xrrci = XRRGetCrtcInfo(d, xrrr, xrrr->crtcs[i]);
        printf("%dx%d+%d+%d\n", xrrci->width, xrrci->height, xrrci->x, xrrci->y);
        XRRFreeCrtcInfo(xrrci);
    }
    XRRFreeScreenResources(xrrr);
    return 0;
}

Answer 2

The accepted answer did not work for me. The correct way I found of doing this was this:

#include <stdio.h>
#include <stdlib.h>
#include <X11/Xlib.h>
#include <X11/extensions/Xrandr.h>

int main(void) {
    Display *display = XOpenDisplay(NULL);

    if (NULL == display) {
        perror("No DISPLAY in environment!");
        exit(EXIT_FAILURE);
    }

    Window window = DefaultRootWindow(display);
    XRRScreenResources *screenr = XRRGetScreenResources(display, window);

    // This is the key right here. Use XRRScreenResources::noutput
    int output = screenr->noutput;

    for (int i = 0; i < output; ++i) {
        XRROutputInfo* out_info = XRRGetOutputInfo(display, screenr, screenr->outputs[i]);

        if (NULL != out_info && out_info->connection == RR_Connected) {
            XRRCrtcInfo* crt_info = XRRGetCrtcInfo(display, screenr, out_info->crtc);
            printf("%s\t%dx%d+%d+%d\n", out_info->name, 
                                        crt_info->width, 
                                        crt_info->height,
                                        crt_info->x,
                                        crt_info->y);
            XRRFreeCrtcInfo(crt_info);
        }

        XRRFreeOutputInfo(out_info);
    }

    XRRFreeScreenResources(screenr);
    XCloseDisplay(display);

    return 0;
}

As I said in the code comment, the trick is using XRRScreenResources::noutput instead of XRRScreenResources::ncrtc