[gtk+] x11: Fallback to emulated window dragging for touch devices

[Carlos Garnacho <carlosg src gnome org>]

commit d1d4c602e09c0038cc8e20f3660859af4378b997
Author: Carlos Garnacho <carlosg gnome org>
Date:   Thu Mar 13 20:19:26 2014 +0100

    x11: Fallback to emulated window dragging for touch devices
    
    Sadly, EWMH moveresize mechanism can't work with touch devices for two
    reasons:
    
    1) As a mutter implementation detail, the device is queried in order
    to check whether the dragging button is still pressed. Touch devices
    won't report the button 1 being pressed through pointer emulation.
    2) Even bypassing that check, on X11 touch events are selected prior
    to sequences being started, either through XISelectEvents or
    XIGrabTouchBegin, no late registering through active grabs is allowed,
    as WMs do on reaction to EWMH moveresize messages.
    
    So for the time being, make touch devices fallback on emulated window
    dragging, which at least allows for moving windows.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=709914

 gdk/x11/gdkwindow-x11.c |   26 ++++++++++++++++++++++----
 1 files changed, 22 insertions(+), 4 deletions(-)
---
diff --git a/gdk/x11/gdkwindow-x11.c b/gdk/x11/gdkwindow-x11.c
index 5696e95..08ef713 100644
--- a/gdk/x11/gdkwindow-x11.c
+++ b/gdk/x11/gdkwindow-x11.c
@@ -5303,6 +5303,24 @@ emulate_move_drag (GdkWindow     *window,
   create_moveresize_window (mv_resize, timestamp);
 }
 
+static gboolean
+_should_perform_ewmh_drag (GdkWindow *window,
+                           GdkDevice *device)
+{
+  GdkPointerWindowInfo *info;
+  GdkDisplay *display;
+
+  display = gdk_window_get_display (window);
+  info = _gdk_display_get_pointer_info (display, device);
+
+  if ((!info->last_slave || gdk_device_get_source (info->last_slave) != GDK_SOURCE_TOUCHSCREEN) &&
+      gdk_x11_screen_supports_net_wm_hint (GDK_WINDOW_SCREEN (window),
+                                           gdk_atom_intern_static_string ("_NET_WM_MOVERESIZE")))
+    return TRUE;
+
+  return FALSE;
+}
+
 static void
 gdk_x11_window_begin_resize_drag (GdkWindow     *window,
                                   GdkWindowEdge  edge,
@@ -5316,8 +5334,8 @@ gdk_x11_window_begin_resize_drag (GdkWindow     *window,
       !WINDOW_IS_TOPLEVEL_OR_FOREIGN (window))
     return;
 
-  if (gdk_x11_screen_supports_net_wm_hint (GDK_WINDOW_SCREEN (window),
-                                          gdk_atom_intern_static_string ("_NET_WM_MOVERESIZE")))
+  /* Avoid EWMH for touch devices */
+  if (_should_perform_ewmh_drag (window, device))
     wmspec_resize_drag (window, edge, device, button, root_x, root_y, timestamp);
   else
     emulate_resize_drag (window, edge, device, button, root_x, root_y, timestamp);
@@ -5341,8 +5359,8 @@ gdk_x11_window_begin_move_drag (GdkWindow *window,
   else
     direction = _NET_WM_MOVERESIZE_MOVE;
 
-  if (gdk_x11_screen_supports_net_wm_hint (GDK_WINDOW_SCREEN (window),
-                                          gdk_atom_intern_static_string ("_NET_WM_MOVERESIZE")))
+  /* Avoid EWMH for touch devices */
+  if (_should_perform_ewmh_drag (window, device))
     wmspec_moveresize (window, direction, device, button, root_x, root_y, timestamp);
   else
     emulate_move_drag (window, device, button, root_x, root_y, timestamp);