DND: Work better with XI2

It turns out that simply using XIGrabKeycode instead of XGrabKey
makes the DND keyboard support mostly work (there seem to be some
minor issues with modifiers). This means we no longer grab the
keyboard actively during DND, which in turn makes Alt-Tab and
other window manager shortcuts work again during DND.

At the same time, bring the DND key handling code into the
multi-backend work, by checking for X11 and XI2 at runtime,
in addition to compile time.

gtk/gtkdnd.c

@@ -36,6 +36,9 @@
 #include <X11/Xlib.h>
 #include <X11/keysym.h>
 #include "gdk/x11/gdkx.h"
+#ifdef XINPUT_2
+#include <X11/extensions/XInput2.h>
+#endif
 #endif
 
 #include "gtkdnd.h"
@@ -396,12 +399,7 @@ gtk_drag_get_ipc_widget (GtkWidget *widget)
   return result;
 }
 
-/* FIXME: modifying the XEvent window as in root_key_filter() isn't
+#if defined (GDK_WINDOWING_X11)
- * going to work with XGE/XI2, since the actual event to handle would
- * be allocated/freed before GDK gets to translate the event.
- * Active grabs on the keyboard are used instead at the moment...
- */
-#if defined (GDK_WINDOWING_X11) && !defined (XINPUT_2)
 
 /*
  * We want to handle a handful of keys during DND, e.g. Escape to abort.
@@ -466,8 +464,34 @@ grab_dnd_keys (GtkWidget *widget,
   guint i;
   GdkWindow *window, *root;
   gint keycode;
+#ifdef XINPUT_2
+  gint deviceid;
+  XIGrabModifiers mods;
+  gint num_mods;
+  XIEventMask evmask;
+  unsigned char mask[(XI_LASTEVENT + 7)/8];
+  gboolean using_xi2;
+
+  deviceid = gdk_x11_device_get_id (device);
+
+  if (GDK_IS_X11_DEVICE_MANAGER_XI2 (gdk_display_get_device_manager (gtk_widget_get_display (widget))))
+    using_xi2 = TRUE;
+  else
+    using_xi2 = FALSE;
+#endif
 
   window = gtk_widget_get_window (widget);
+  if (!GDK_IS_X11_WINDOW (window))
+    {
+      gdk_device_grab (device,
+                       gtk_widget_get_window (widget),
+                       GDK_OWNERSHIP_APPLICATION, FALSE,
+                       GDK_KEY_PRESS_MASK | GDK_KEY_RELEASE_MASK,
+                       NULL, time);
+      return;
+    }
+
+
   root = gdk_screen_get_root_window (gtk_widget_get_screen (widget));
 
   gdk_error_trap_push ();
@@ -477,12 +501,45 @@ grab_dnd_keys (GtkWidget *widget,
       keycode = XKeysymToKeycode (GDK_WINDOW_XDISPLAY (window), grab_keys[i].keysym);
       if (keycode == NoSymbol)
         continue;
-      XGrabKey (GDK_WINDOW_XDISPLAY (window),
+
-   	        keycode, grab_keys[i].modifiers,
+#ifdef XINPUT_2
-	        GDK_WINDOW_XID (root),
+      if (using_xi2)
-	        FALSE,
+        {
-	        GrabModeAsync,
+          memset (mask, 0, sizeof (mask));
-	        GrabModeAsync);
+          XISetMask (mask, XI_KeyPress);
+          XISetMask (mask, XI_KeyRelease);
+
+          evmask.deviceid = deviceid;
+          evmask.mask_len = sizeof (mask);
+          evmask.mask = mask;
+
+          if (grab_keys[i].modifiers != 0)
+            {
+              num_mods = 1;
+              mods.modifiers = grab_keys[i].modifiers;
+            }
+          else
+            num_mods = 0;
+
+          XIGrabKeycode (GDK_WINDOW_XDISPLAY (window),
+                         deviceid,
+                         keycode,
+                         GDK_WINDOW_XID (root),
+                         GrabModeAsync,
+                         GrabModeAsync,
+                         False,
+                         &evmask,
+                         num_mods,
+                         &mods);
+        }
+      else
+#endif
+        XGrabKey (GDK_WINDOW_XDISPLAY (window),
+                  keycode, grab_keys[i].modifiers,
+                  GDK_WINDOW_XID (root),
+                  FALSE,
+                  GrabModeAsync,
+                  GrabModeAsync);
     }
 
   gdk_flush ();
@@ -499,8 +556,26 @@ ungrab_dnd_keys (GtkWidget *widget,
   guint i;
   GdkWindow *window, *root;
   gint keycode;
+#ifdef XINPUT_2
+  XIGrabModifiers mods;
+  gint num_mods;
+  gint deviceid;
+  gboolean using_xi2;
+
+  deviceid = gdk_x11_device_get_id (device);
+  if (GDK_IS_X11_DEVICE_MANAGER_XI2 (gdk_display_get_device_manager (gtk_widget_get_display (widget))))
+    using_xi2 = TRUE;
+  else
+    using_xi2 = FALSE;
+#endif
 
   window = gtk_widget_get_window (widget);
+  if (!GDK_IS_X11_WINDOW (window))
+    {
+      gdk_device_ungrab (device, time);
+      return;
+    }
+
   root = gdk_screen_get_root_window (gtk_widget_get_screen (widget));
 
   gdk_window_remove_filter (NULL, root_key_filter, (gpointer) GDK_WINDOW_XID (window));
@@ -512,16 +587,37 @@ ungrab_dnd_keys (GtkWidget *widget,
       keycode = XKeysymToKeycode (GDK_WINDOW_XDISPLAY (window), grab_keys[i].keysym);
       if (keycode == NoSymbol)
         continue;
-      XUngrabKey (GDK_WINDOW_XDISPLAY (window),
+
-      	          keycode, grab_keys[i].modifiers,
+#ifdef XINPUT_2
-                  GDK_WINDOW_XID (root));
+      if (using_xi2)
+        {
+          if (grab_keys[i].modifiers != 0)
+            {
+              num_mods = 1;
+              mods.modifiers = grab_keys[i].modifiers;
+            }
+          else
+            num_mods = 0;
+
+          XIUngrabKeycode (GDK_WINDOW_XDISPLAY (window),
+                           deviceid,
+                           keycode,
+                           GDK_WINDOW_XID (root),
+                           num_mods,
+                           &mods);
+        }
+      else
+#endif
+        XUngrabKey (GDK_WINDOW_XDISPLAY (window),
+                    keycode, grab_keys[i].modifiers,
+                    GDK_WINDOW_XID (root));
     }
 
   gdk_flush ();
   gdk_error_trap_pop_ignored ();
 }
 
-#else /* GDK_WINDOWING_X11 && !XINPUT_2 */
+#else /* !GDK_WINDOWING_X11 */
 
 static void
 grab_dnd_keys (GtkWidget *widget,
@@ -4316,7 +4412,7 @@ gtk_drag_key_cb (GtkWidget         *widget,
   if (event->type == GDK_KEY_PRESS)
     {
       switch (event->keyval)
-{
+        {
         case GDK_KEY_Escape:
           gtk_drag_cancel (info, GTK_DRAG_RESULT_USER_CANCELLED, event->time);
           return TRUE;