[Spice-devel] [spice-gtk v2] mouse: Fix pointer grabbing in server mode

[Christophe Fergeau]

Trying to click on spice-gtk window while in server mode should result
in a pointer grab. This is currently failing, with the cursor wrapping
to the top left corner of the window instead without being grabbed.

This is caused by our use of gtk_event_box_set_above_child(),
when clicking on the SpiceWidget, the grab is implicitly taken by
the window which is above the event box (which is an internal
GtkEventBox input-only GdkWindow). Then when we call gdk_pointer_grab()
on the GtkEventBox::window, we get a grab-broken event indicating the
grab was transferred from the internal input-only window to
GtkEventBox::window (see gtk+ bug
https://bugzilla.gnome.org/show_bug.cgi?id=769635#c2 for a detailed
explanation).

This commit ignores grab-broken events when the GdkWindow who got the
grab corresponds to the one we called gdk_pointer_grab() on.
An alternative would be to call gdk_pointer_grab() on the GdkWindow
which received the button-press-event, but the call chain between
button_event() and the eventual gdk_pointer_grab() call, so it would be
not so elegant to pass the correct GdkWindow all the way.
---
Changes since v1:

Rework commit log/code comment following garnacho's input in the gtk+ bug. No
code change.


 src/spice-widget.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/src/spice-widget.c b/src/spice-widget.c
index 7c1c756..de10736 100644
--- a/src/spice-widget.c
+++ b/src/spice-widget.c
@@ -462,8 +462,19 @@ static GdkCursor* get_blank_cursor(void)
 static gboolean grab_broken(SpiceDisplay *self, GdkEventGrabBroken *event,
                             gpointer user_data G_GNUC_UNUSED)
 {
+    GdkWindow *window = gtk_widget_get_window(GTK_WIDGET(self));
     SPICE_DEBUG("%s (implicit: %d, keyboard: %d)", __FUNCTION__,
                 event->implicit, event->keyboard);
+    SPICE_DEBUG("%s (SpiceDisplay::GdkWindow %p, event->grab_window: %p)",
+                __FUNCTION__, window, event->grab_window);
+    if (window == event->grab_window) {
+        /* ignore grab-broken event moving the grab to GtkEventBox::window
+         * (from GtkEventBox::event_window) as we initially called
+         * gdk_pointer_grab() on GtkEventBox::window, see
+         * https://bugzilla.gnome.org/show_bug.cgi?id=769635
+         */
+        return false;
+    }
 
     if (event->keyboard) {
         try_keyboard_ungrab(self);
-- 
2.7.4