How to use xlib to listen for screen resolution changes on Linux

Question

I am writing a small proprietary procedure to notify another process that the user has changed the screen resolution. I tried using gtk, but it is unstable for non-shared window managers and often crashes. I am learning xlib and have an example of work that notifies me when the generated size of the X Window changes, but I cannot figure out how to get a notification that the screen resolution has changed. Any help would be greatly appreciated. I include my xlib test code and gtk + test code, which, as indicated, crashes badly when using non-component window managers.

Here is my test code using xlib

Display * display; int screen; Window root, window; display = XOpenDisplay (NULL); if (!display){ syslog(LOG_INFO, "Could not open display.\n"); } screen = DefaultScreen(display); root = RootWindow(display, screen); window = XCreateSimpleWindow (display, root, 0, 0, 300, 300, // xpos, ypos, width, height 0, 0, // border width, border pixel 0 /* background */); // Add StructureNotifyMask to send us events involving resizing of the window, etc. XSelectInput (display, window, ExposureMask | StructureNotifyMask); XMapWindow (display, window); while (1){ XEvent e; XNextEvent (display, &e); // Respond to ConfigureNotify, the type of event sent by the // server if the window is resized. if (e.type == ConfigureNotify){ XConfigureEvent xce = e.xconfigure; /* This event type is generated for a variety of happenings, so check whether the window has been resized. */ syslog(LOG_INFO, "New Width,Height %d,%d", xce.width, xce.height); } } 

Test code using GTK +

 GtkWidget *window; GdkScreen *screen; screen = gdk_screen_get_default(); window = gtk_window_new(GTK_WINDOW_TOPLEVEL); syslog(LOG_INFO, "NATIVESUPPORT: startDisplayChangedEventThread(): screen and window objects created.\n"); if (!screen){ syslog(LOG_INFO, "NATIVESUPPORT: screen is null."); } if (!window){ syslog(LOG_INFO, "NATIVESUPPORT: window is null."); } g_signal_connect(screen, "size-changed", G_CALLBACK(resize_cb), (gpointer)window); g_signal_connect(screen, "monitors-changed", G_CALLBACK(resize_cb), (gpointer)window); syslog(LOG_INFO, "NATIVESUPPORT: startDisplayChangedEventThread(): call back created.\n"); syslog(LOG_INFO, "NATIVESUPPORT: startDisplayChangedEventThread(): starting main.\n"); gtk_main(); 

Answer 1

The solution was to map to the default root window.

  display = XOpenDisplay (NULL); if (!display) { syslog(LOG_INFO, "Could not open display.\n"); } screen = DefaultScreen (display); root = RootWindow (display, screen); window = DefaultRootWindow( display ); if ( 0 > window ) { syslog(LOG_INFO, "Failed to obtain the root windows Id of the default screen of given display.\n"); } Status ret = XGetWindowAttributes( display, window, &xwAttr ); width = xwAttr.width; height = xwAttr.height; XSelectInput (display, window, ExposureMask | /* Add StructureNotifyMask to send us events involving resizing of the window, etc. */ StructureNotifyMask); XMapWindow (display, window);