Add -transient-window mode

This will add a new mode for the rofi window so when you run it with
-transient-window

instead of
-normal-window

it will get the currently focused window and then use that as the parent window and set itself as transient of that window.  It is useful so that when you  use a keyboard shortcut to start rofi it will always popup on the window you are working on and so it doesn't make you refocus/move your head on large monitors :)

include/view.h

@@ -56,6 +56,8 @@ typedef enum {
   MENU_NORMAL_WINDOW = 2,
   /** ERROR dialog */
   MENU_ERROR_DIALOG = 4,
+  /** Create transient window. */
+  MENU_TRANSIENT_WINDOW = 8,
 } MenuFlags;
 
 /**

source/rofi.c

@@ -768,6 +768,9 @@ static gboolean startup(G_GNUC_UNUSED gpointer data) {
   if (find_arg("-normal-window") >= 0) {
     window_flags |= MENU_NORMAL_WINDOW;
   }
+  if (find_arg("-transient-window") >= 0) {
+    window_flags |= MENU_TRANSIENT_WINDOW;
+  }
   TICK_N("Grab keyboard");
   __create_window(window_flags);
   TICK_N("Create Window");

source/view.c

@@ -1120,7 +1120,25 @@ void __create_window(MenuFlags menu_flags) {
 
   TICK_N("textbox setup");
   // // make it an unmanaged window
-  if (((menu_flags & MENU_NORMAL_WINDOW) == 0)) {
+  if (((menu_flags & MENU_TRANSIENT_WINDOW) != 0)) {
+    xcb_atom_t atoms[] = {xcb->ewmh._NET_WM_STATE_MODAL};
+
+    window_set_atom_prop(box_window, xcb->ewmh._NET_WM_STATE, atoms,
+                         sizeof(atoms) / sizeof(xcb_atom_t));
+    window_set_atom_prop (box_window, xcb->ewmh._NET_WM_WINDOW_TYPE,
+                          &(xcb->ewmh._NET_WM_WINDOW_TYPE_UTILITY), 1);
+    x11_disable_decoration(box_window);
+
+    xcb_window_t active_window;
+    xcb_get_property_cookie_t awc;
+    awc = xcb_ewmh_get_active_window (&xcb->ewmh, xcb->screen_nbr);
+
+    if (xcb_ewmh_get_active_window_reply(&xcb->ewmh, awc, &active_window, NULL)) {
+        xcb_change_property(xcb->connection, XCB_PROP_MODE_REPLACE, box_window,
+                            XCB_ATOM_WM_TRANSIENT_FOR, XCB_ATOM_WINDOW, 32,
+                            1, &active_window);
+    }
+  } else if (((menu_flags & MENU_NORMAL_WINDOW) == 0)) {
     window_set_atom_prop(box_window, xcb->ewmh._NET_WM_STATE,
                          &(xcb->ewmh._NET_WM_STATE_ABOVE), 1);
     uint32_t values[] = {1};