Implement support for the wp_pointer_constraints protocol

The wp_pointer_constraints protocol is a protocol which enables clients
to manipulate the behavior of the pointer cursor associated with a seat.

Currently available constraints are locking the pointer to a static
position, and confining the pointer to a given region.

Currently locking is fully implemented, and confining is implemented for
rectangular confinement regions.

What else is lacking is less troublesome semantics for enabling the lock
or confinement; currently the only requirement implemented is that the
window that appears focused is the one that may aquire the lock.

This means that a pointer could be 'stolen' by creating a new window that
receives active focus, or when using focus-follows-mouse, a pointer
passes a window that has requested a lock. This semantics can be changed
and the protocol itself allows any semantics as seems fit.

https://bugzilla.gnome.org/show_bug.cgi?id=744104

src/backends/meta-pointer-constraint.c

@@ -0,0 +1,57 @@
+/* -*- mode: C; c-file-style: "gnu"; indent-tabs-mode: nil; -*- */
+
+/*
+ * Copyright (C) 2015 Red Hat
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+ * 02111-1307, USA.
+ *
+ * Written by:
+ *     Jonas Ådahl <jadahl@gmail.com>
+ */
+
+#include "config.h"
+
+#include "backends/meta-pointer-constraint.h"
+
+#include <glib-object.h>
+
+G_DEFINE_TYPE (MetaPointerConstraint, meta_pointer_constraint, G_TYPE_OBJECT);
+
+static void
+meta_pointer_constraint_init (MetaPointerConstraint *constraint)
+{
+}
+
+static void
+meta_pointer_constraint_class_init (MetaPointerConstraintClass *klass)
+{
+}
+
+void
+meta_pointer_constraint_constrain (MetaPointerConstraint *constraint,
+                                   ClutterInputDevice    *device,
+                                   guint32                time,
+                                   float                  prev_x,
+                                   float                  prev_y,
+                                   float                  *x,
+                                   float                  *y)
+{
+  META_POINTER_CONSTRAINT_GET_CLASS (constraint)->constrain (constraint,
+                                                             device,
+                                                             time,
+                                                             prev_x, prev_y,
+                                                             x, y);
+}