evdev: Pass a motion delta to pointer constrain callback

The constrain callback cannot rely on the pointer position of the
corresponding ClutterInputDevice to get the actual delta of the motion
event that is to be constrained since it is only updated when an event is
dispatched. So change the API to pass the previous pointer position when
constraining.

https://bugzilla.gnome.org/show_bug.cgi?id=752752

README.in

@@ -289,6 +289,13 @@ Relevant information for developers with existing Clutter applications
 wanting to port to newer releases (see NEWS for general information on new
 features).
 
+Release Notes for Clutter 1.26
+-------------------------------------------------------------------------------
+
+• The evdev backend specific ClutterPointerConstrainCallback type was changed
+  to include not only the target position but also the previous position. This
+  is an API change, and will require a version check in any caller code.
+
 Release Notes for Clutter 1.24
 -------------------------------------------------------------------------------
 

clutter/evdev/clutter-device-manager-evdev.c

@@ -452,7 +452,10 @@ new_absolute_motion_event (ClutterInputDevice *input_device,
   if (manager_evdev->priv->constrain_callback)
     {
       manager_evdev->priv->constrain_callback (seat->core_pointer,
-                                               us2ms (time_us), &x, &y,
+                                               us2ms (time_us),
+                                               seat->pointer_x,
+                                               seat->pointer_y,
+                                               &x, &y,
 					       manager_evdev->priv->constrain_data);
     }
   else

clutter/evdev/clutter-evdev.h

@@ -82,6 +82,8 @@ void  clutter_evdev_reclaim_devices (void);
  */
 typedef void (*ClutterPointerConstrainCallback) (ClutterInputDevice *device,
 						 guint32             time,
+						 float               prev_x,
+						 float               prev_y,
 						 float              *x,
 						 float              *y,
 						 gpointer            user_data);