added addObserver function to layer

vtk/src/helperClasses/Layer.cpp

@@ -1,4 +1,6 @@
 #include "Layer.h"
+#include <vtkRenderWindow.h>
+#include <vtkRenderWindowInteractor.h>
 
 using std::string;
 
@@ -8,3 +10,8 @@ vtkSmartPointer<vtkRenderer> Layer::getLayer() {
 
 void Layer::updateData(int t) {
 }
+
+
+void Layer::addObserver(const char *event, vtkCommand *observer) {
+  this->getLayer()->GetRenderWindow()->GetInteractor()->AddObserver(event, observer);
+}

vtk/src/helperClasses/Layer.h

@@ -1,6 +1,7 @@
 #ifndef LAYER_H
 #define LAYER_H
 
+#include <vtkInteractorStyle.h>
 #include <vtkRenderer.h>
 
 /** This class represents one abstract layer to be rendered to VTK.
@@ -21,6 +22,12 @@ public:
     * @param t : the timestamp which the data should reflect.
     */
   virtual void updateData(int t);
+
+  /** Adds an observer to the renderWindowinteractor within which this layer is active.
+    * @param event : the specific event type to subscribe to (see the vtkCommand::EventIds enum) 
+    * @param observer : the observer to add.
+    */
+  virtual void addObserver(const char *event, vtkCommand *observer);
 };
 
 #endif