Moving windows between separate X screens

Question

I've just switched over to using separate X screens for various different reasons and the only thing I can't get sorted is to find a way to move a window from one screen to another. I've tried 'xmove' and 'wmctrl' so far but had no joy. I don't want to go back to using twinview and searching around the usual supects is turning up nothing besides what i've already mentioned.
From what i've read it's (quite easily) do-able on other platforms but does anyone know if this is possible on Linux?

Answer 1

I believe this can be done, at least from GTK level. Here is a short example of how this can be achieved:
#include <gtk/gtk.h>
#include <gdk/gdk.h>
GtkWindow * mainWindow;
GdkDisplay *second_display;
GdkScreen *second_screen;
static void print_hello (GtkWidget *widget, gpointer data)
g_print ("Hello World\n");
GdkScreen* screen = gtk_window_get_screen(mainWindow);
gint number = gdk_screen_get_number(screen);
g_print ("Opened in screen %d \n",number);
gtk_window_set_screen (mainWindow, second_screen);
screen = gtk_window_get_screen(mainWindow);
number = gdk_screen_get_number(screen);
g_print ("Now in screen %d \n",number);
int main (int argc, char *argv[])
GtkWidget *window;
GtkWidget *button;
gtk_init (&argc, &argv);
second_display = gdk_display_open (":0.1");
second_screen = gdk_display_get_default_screen (second_display);
window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
mainWindow = GTK_WINDOW(window);
gtk_window_set_title (GTK_WINDOW (window), "Hello");
g_signal_connect (window, "destroy", G_CALLBACK (gtk_main_quit), NULL);
gtk_container_set_border_width (GTK_CONTAINER (window), 10);
button = gtk_button_new_with_label ("Hello World");
g_signal_connect (button, "clicked", G_CALLBACK (print_hello), NULL);
gtk_container_add (GTK_CONTAINER (window), button);
gtk_widget_show (button);
gtk_widget_show (window);
gtk_main ();
return 0;
This is modified from hello world example of gtk. Save the code to simple.c, then it should be compiled with:
gcc -o simple simple.c `pkg-config --libs --cflags gtk+-2.0`
The program will be started with a button inside, on where you start it. When button is clicked, the window will be move to the screen with display name ":0.1", you can change that value in source code to have it move to other screen.
As far as I known, Gimp and emacs utilized this ability so that you can move their windows to other screen.
I am not comfirmed but I think there is a similiar way to do so in QT. So if a program use either GTK or QT, its windows is capable to move to other screens.
I do not know whether this can be done in Xlib or Xcb, and how this is done in GTK. Maybe they re-created a new X window and re-map everything to that container. So maybe it is hard to control in Window Managers. Its upon the developer of applications to make this ability available.