Finding out the size of taskbar in Linux (C/C++/gtkmm/other)

Question

How can I find the effective working are of my Linux desktop (by which I mean: screen's height - taskbar's height)?

I need this for my program, which I am writing in c++/gtkmm. I want to position the window in the bottom-right corner of the screen, above the taskbar.

At first I tried to maximize the window, check its height and subtract it from screen's height. For some reason it gives me the height before the maximalization, so it doesn't work.

Answer 1

You need to wait for the map-event event before checking the size of your window.

Unlike what apmasell and senshikaze stated, you can quite reliably do this using GTK+. However, you should connect to the relevant signals (map-event, configure-event, screen-changed, visibility-notify-event and maybe window-state-event), so your small window will correctly move/resize, when screen resolution or toolbars change.

For example, I personally use two auto-hidden bars on XFCE4. If there is a small tool window "docked" to the bottom right corner, I want it to move out of the way when my bottom bar is shown.

If the window is a pure notification window, then I agree with apmasell that you're best off using libnotify (for example, run notify-send ... as a child process) to generate a normal notification window.

As a proof of concept, here is a small C program, size.c, which obtains the information using a fully transparent undecorated window:

#include <gtk/gtk.h>
#include <gdk/gdk.h>
#include <stdio.h>

int screen_width = -1;
int screen_height = -1;

int window_left = -1;
int window_top = -1;
int window_width = -1;
int window_height = -1;

void done(GtkWidget *widget, void *payload)
{
    GdkScreen *screen = gtk_widget_get_screen(widget);

    screen_width = gdk_screen_get_width(screen);
    screen_height = gdk_screen_get_height(screen);

    gtk_window_get_position((GtkWindow *)widget, &window_left, &window_top);
    gtk_window_get_size((GtkWindow *)widget, &window_width, &window_height);

    gtk_widget_destroy(widget);
    gtk_main_quit();
}

int main(int argc, char *argv[])
{
    GtkWidget *window;

    gtk_init(&argc, &argv);
    window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    gtk_window_set_opacity((GtkWindow *)window, 0.0);
    gtk_window_set_decorated((GtkWindow *)window, (gboolean)FALSE);
    gtk_window_maximize((GtkWindow *)window);
    gtk_widget_show(window);

    g_signal_connect(window, "map-event", G_CALLBACK(done), NULL);
    gtk_main();

    if (screen_width > 0 && screen_height > 0)
        printf("Screen is %d x %d pixels\n", screen_width, screen_height);

    if (window_width > 0 && window_height > 0)
        printf("Window is %d x %d pixels\n", window_width, window_height);

    if (window_left > 0)
        printf("There is a %d pixel wide left bar\n", window_left);

    if (window_left >= 0 && window_width > 0 && screen_width > 0 && window_width + window_left < screen_width)
        printf("There is a %d pixel wide right bar\n", screen_width - (window_width + window_left));

    if (window_top > 0)
        printf("There is a %d pixel tall top bar\n", window_top);

    if (window_top >= 0 && window_height > 0 && screen_height > 0 && window_height + window_top < screen_height)
        printf("There is a %d pixel tall bottom bar\n", screen_height - (window_height + window_top));

    return 0;
}

Compile using

gcc -W -Wall size.c `pkg-config --cflags --libs gtk+-3.0` -o size

or, if still using GTK+ 2,

gcc -W -Wall size.c `pkg-config --cflags --libs gtk+-2.0` -o size

Run using ./size. Note that the test program only provides a snapshot; a real program should connect to the aforementioned signals to detect screen or toolbar changes, and update the window size/position accordingly.

Hope you find this useful.