Ok, long time no code, I think I would better to pick the vim and git again before forget everything about coding. 
Yes, I am back as a gtkmm(c++) learner! 
[attachment=0]experiemntalui-2013-11-19.png[/attachment]
Welcome back!
The UI needs a lot of cleaning (I see it overloaded), but each trip starts with a first step!
Good work!
-G
Cool!
Could we perhaps move the save/undo/etc. buttons to a toolbox of it’s own to free even more space?
I am experiencing the main toolbar as GLOBAL toolbar, the buttons except [new][open][save][save all] you see at the above screen will be removed and those tools which effect global scope will be locating on this toolbar, the default interpolate mode for example.
Not sure if it is ok design, but please give me some time, the long term in my plan, the toolbars, main toolbar and all local toolbars owned by panel windows will be fully customizable by user.
a small step, finally i get it and now each canvas window has its own local toolbar properly.
next step is to cleanup all action definition, and of course, the main menubar will be re-organized as well.
[attachment=0]canvas_window_local_toolbar_Screen Shot 2013-12-05.png[/attachment]