What: [incr Tk] Slate megawidget
 Where: http://ptolemy.eecs.berkeley.edu/%7Ejohnr/archives/code/slate/
 Description: The Slate is an [incr Tcl] megawidget layered over the Tcl/Tk
        canvas.  It contains visual hierarchy, symbolic item aspects and
        interaction support.  Release 3.0alpha supports
        Tcl 8.0 or [incr Tcl] 3.0.
 Updated: 07/1998
 Contact: mailto:johnr@EECS.Berkeley.EDU (John Reekie)

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[JMN] 2007-01-28 The entire ptolemy system seems to have migrated to Java a while ago - but there are still earlier versions available which include the Tcl slate code.
It's under a BSD style license and includes some very interesting features such as 'interactors'.
From the documentation:
 Interactors package common patterns of user interaction into reusable objects.
 They are a mechanism originally developed in Brad Meyer's Garnet system

With a bit of mucking about I was able to get most of the slate demos running under Tcl 8.5 - and it seems to me that the code may be worth rescuing. 

see also - The Tycho Slate: Complex Drawing and Editing in Tcl/Tk[http://www.usenix.org/publications/library/proceedings/tcl98/full_papers/reekie/reekie_html/reekie.html]

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