I writed an eclipse plugin that visualize some Java classes as UML in a view part. You choose a package in the Package Explorer and after rigth click on the package you can visualized it by clicking on a self created command menuitem in the menu. The visualization is created with the prefuse library.
My next goal was to make it possible to use it for multitouch. I use the Multitouch Library from PQLabs multitouch SDK. Now, on a multitouch screen, I can move my UML model, resize it etc.
But I was not able to get the informations from the Package Explorer. I tried to find out the location of the Package Explorer and IJavaElements on the screen but failed. My idea was to compare the x and y points from my finger (which I get from the PQL Labs SDK) with the x and y coordinates from the IJavaElements. I failed from the start, I could not be able that a touch point recognizes if it is in the border of the Package Explorer view or not. The only thing I got was the bounds of the whole Display. I searched the internet and stackoverflow but did not find something that was useful.
I do not know if it is possible or not but I will appreciate when somebody can give me information or directed me to good links.
I don’t know much about the Package Explorer, but with the Project Explorer (Common Navigator) (which you should also address), there is a TreeViewer associated with it (in this case the class is CommonViewer). You can get that by doing CommonNavigator.getCommonViewer(). Once you have the TreeViewer, you can then get to the underlying SWT Tree and from there use the standard SWT methods to get the position of the tree relative to the enclosing window. There are also methods where you can get the bounds of a tree cell. Have a look at the SWT Snippets (Google it) to help you work with the Tree.
For the Package Explorer it will be similar; you will have to look at the source code.