Drag and Drop in TreeView - need to convert y coordinate?

[Edvin Syse]

My TreeView has a DragSource and DropTarget used to allow moving nodes 
around. In DropTarget#drop, I try to get the node the user dropped on 
like this:

Sequence.Tree.get(getTreeData(), getNodeAt(y))
.. but it seems y is relative to the window, and getNodeAt() expects 
coordinates relative to the component (TreeView). Is there method to 
convert the coordinates, or should I use another approach?

-- Edvin