--- a/Framework/Layers/LineMeasureTracker.h	Wed Oct 17 15:18:48 2018 +0200
+++ b/Framework/Layers/LineMeasureTracker.h	Wed Oct 17 19:38:39 2018 +0200
@@ -49,7 +49,12 @@
                        uint8_t green,
                        uint8_t blue,
                        unsigned int fontSize);
-    
+
+    virtual bool HasRender() const
+    {
+      return true;
+    }
+
     virtual void Render(CairoContext& context,
                         double zoom);
     
@@ -62,7 +67,9 @@
       // Possibly create a new landmark "volume" with the line in subclasses
     }
 
-    virtual void MouseMove(double x,
+    virtual void MouseMove(int displayX,
+                           int displayY,
+                           double x,
                            double y);
   };
 }