Handle Markups events from an external module

[Fangwen_Zhai (fangwenz)]

@lassoan

I’ve added a new pair of events (available in Slicer Preview Release from tomorrow): slicer.vtkMRMLMarkupsNode.PointPositionDefinedEvent and slicer.vtkMRMLMarkupsNode.PointPositionUndefinedEvent. These are only invoked when a point is placed or a placed point is removed. Not impacted by point previews.

def onMarkupPointPositionDefined(caller, event):
    markupsNode = caller
    movingMarkupIndex = markupsNode.GetDisplayNode().GetActiveControlPoint()
    logging.info(f"Markup point added: point ID = {movingMarkupIndex}")

def onMarkupPointPositionUndefined(caller, event):
    markupsNode = caller
    movingMarkupIndex = markupsNode.GetDisplayNode().GetActiveControlPoint()
    logging.info(f"Markup point removed: point ID = {movingMarkupIndex}")

markupsNode = slicer.mrmlScene.AddNewNodeByClass("vtkMRMLMarkupsFiducialNode")
markupsNode.CreateDefaultDisplayNodes()
markupsNode.AddFiducial(0,0,0)
markupsNode.AddObserver(slicer.vtkMRMLMarkupsNode.PointPositionDefinedEvent, onMarkupPointPositionDefined)
markupsNode.AddObserver(slicer.vtkMRMLMarkupsNode.PointPositionUndefinedEvent, onMarkupPointPositionUndefined)

As to the two events, there may be a bug in bool vtkMRMLMarkupsNode::InsertControlPoint(ControlPoint *controlPoint, int targetIndex), line 689 of vtkMRMLMarkupsNode.cxx:

// let observers know that a markup was added
  this->InvokeCustomModifiedEvent(vtkMRMLMarkupsNode::PointAddedEvent, static_cast<void*>(&targetIndex));
  if (controlPoint->PositionStatus == vtkMRMLMarkupsNode::PositionDefined)
    {
    this->InvokeCustomModifiedEvent(vtkMRMLMarkupsNode::PointPositionUndefinedEvent, static_cast<void*>(&targetIndex));
    }
  this->UpdateMeasurements();

I think PointPositionUndefinedEvent should be PointPositionDefinedEvent?