   
   override func mouseDown(theEvent: NSEvent) {
     sprint("canvasView: mouse down")
+    let point = convertPoint(theEvent.locationInWindow, fromView: nil)
+    clicks.append(point)
+    
     for concept in concepts {
       concept.editing = false
     }

    if mode == Mode.Concepts {
      for concept in concepts { addConceptView(concept) }
    }
  }
  
  // MARK: - Drawing Functions

}

class CanvasView: NSView {
  var delegate: CanvasViewDelegate?
  var mode: Mode?
  var concepts = [Concept]() { didSet { needsDisplay = true } }
  var links = [Link]() { didSet { needsDisplay = true } }
  var arrowStart: NSPoint? { didSet { needsDisplay = true } }
  var arrowEnd: NSPoint? { didSet { needsDisplay = true } }
  var clicks = [NSPoint]() { didSet { needsDisplay = true } }
  var originConceptIdentifier: Int?
  var targetConceptIdentifier: Int?
  
