Introduce geometry conversion helpers

The new helpers are designed for the purpose of mapping points from the
global screen coordinates to the frame-local and the surface-local coords

input.cpp

@@ -1714,7 +1714,7 @@ public:
 
         switch (event->type()) {
         case QEvent::TabletMove: {
-            const auto pos = event->globalPosF() - toplevel->bufferGeometry().topLeft();
+            const auto pos = toplevel->mapToLocal(event->globalPosF());
             tool->sendMotion(pos);
             m_cursorByTool[tool]->setPos(event->globalPos());
             break;
@@ -1725,7 +1725,7 @@ public:
             tool->sendProximityOut();
             break;
         case QEvent::TabletPress: {
-            const auto pos = event->globalPosF() - toplevel->bufferGeometry().topLeft();
+            const auto pos = toplevel->mapToLocal(event->globalPosF());
             tool->sendMotion(pos);
             m_cursorByTool[tool]->setPos(event->globalPos());
             tool->sendDown();

toplevel.cpp

@@ -789,6 +789,21 @@ QMatrix4x4 Toplevel::inputTransformation() const
     return m;
 }
 
+QPoint Toplevel::mapToFrame(const QPoint &point) const
+{
+    return point - frameGeometry().topLeft();
+}
+
+QPoint Toplevel::mapToLocal(const QPoint &point) const
+{
+    return point - bufferGeometry().topLeft();
+}
+
+QPointF Toplevel::mapToLocal(const QPointF &point) const
+{
+    return point - bufferGeometry().topLeft();
+}
+
 quint32 Toplevel::windowId() const
 {
     return window();

toplevel.h

@@ -381,6 +381,18 @@ public:
     virtual bool isClient() const;
     virtual bool isDeleted() const;
 
+    /**
+     * Maps the specified @a point from the global screen coordinates to the frame coordinates.
+     */
+    QPoint mapToFrame(const QPoint &point) const;
+    /**
+     * Maps the specified @a point from the global screen coordinates to the surface-local
+     * coordinates of the main surface. For X11 clients, this function maps the specified point
+     * from the global screen coordinates to the buffer-local coordinates.
+     */
+    QPoint mapToLocal(const QPoint &point) const;
+    QPointF mapToLocal(const QPointF &point) const;
+
     // prefer isXXX() instead
     // 0 for supported types means default for managed/unmanaged types
     virtual NET::WindowType windowType(bool direct = false, int supported_types = 0) const = 0;