Entry and exit events from MRML slice views

Development
1

I’m hoping to perform actions in my scripted module when the user’s mouse enters or exits the Red and Yellow MRML slice views. I know this involves observing events, but I’m not sure what event to observe, and where to use AddObserver. How can I accomplish this?
Thanks.

2

These are standard VTK interaction events that you can get by observing low-level VTK objects (probably the interactor; see examples of accessing these low-level objects in the script repository).

However, I would recommend to use higher-level API, such as observing the crosshair node. You can get the current slice node using vtkMRMLCrosshairNode::GetCursorPositionXYZ method.

1 Like
3

Excellent, thank you. I’m able to get the slice node and its name that way.
I am using a ctkWorkflow, and I’ve also set it up to add the observer when advancing to the relevant step, and remove the observer afterwards:

def onEntry(self):
    ...
    self.crosshairNode=slicer.util.getNode('Crosshair')
    self.crosshairNodeObserverTag = self.crosshairNode.AddObserver(slicer.vtkMRMLCrosshairNode.CursorPositionModifiedEvent, self.onMouseMoved)
#end onEntry

def onExit(self):
    if(self.crosshairNodeObserverTag is not None):
        self.crosshairNode.RemoveObserver(self.crosshairNodeObserverTag)
#end onExit
1 Like
4

I am creating a crosshairnode but still the program shows erroe crosshairnode not defined

self.crosshairNode=slicer.mrmlScene.AddNewNodeByClass("vtkMRMLCrosshairNode")
self.observeid = self.crosshairNode.AddObserver(slicer.vtkMRMLCrosshairNode.CursorPositionModifiedEvent, self.onMouseMoved)
5

There is a singleton crosshair node, which is used by the application. You need to retrieve and use that node, as shown in the examples (do not create a new crosshair node).