for( int i = 0; i < 4; ++i )
   {
     if( this->m_Windows[ i ] == NULL )
+    {
+      this->m_Renderers[ i ] = NULL;
       continue;
 
+    } // fi
+
     // Renderers
     this->m_Renderers[ i ] = vtkSmartPointer< vtkRenderer >::New( );
     this->m_Renderers[ i ]->SetBackground( 0.1, 0.3, 0.8 );
     );
 
   // Correct cameras positions
-  vtkCamera* zCam = this->m_Renderers[ 2 ]->GetActiveCamera( );
-  zCam->SetViewUp( 0, -1, 0 );
-  zCam->SetPosition( 0, 0, -1 );
-  zCam->SetFocalPoint( 0, 0, 0 );
+  /* TODO
+     vtkCamera* zCam = this->m_Renderers[ 2 ]->GetActiveCamera( );
+     zCam->SetViewUp( 0, -1, 0 );
+     zCam->SetPosition( 0, 0, -1 );
+     zCam->SetFocalPoint( 0, 0, 0 );
+  */
 
   // First rendering
   this->ResetCameras( );