Question about updating in a GUI

[Gheorghe Postelnicu]

Hi,

I have a GUI which does some visualization based on VTK and Tkinter.

The problem I have is kinda complicated to describe, but here is a
sketch of it: I have a basic Observer pattern in place for events
(such as the change current 2D slice visualized) and it generally
works well.

However, I just tried inserting a new mode in my GUI, which triggers
an update in the above interface. In general, modes react to these
event changes by refreshing the data, so the code is really
straightforward. However, for this specific mode, I need some
persistent data. So I need to tell my Callback to keep the data and
not refresh it, as is usually the case.

I tried to set a flag that would be set during this operation (my
application is not multi-threaded and I took a chance), but the
updates in the renderer in VTK are not synchronous, so the flag gets
cleared before all the updates occured, so my data still gets flushed
away.

Any suggestions on how I should be approaching this?

Thanks,
-- 
Gheorghe Postelnicu, PhD
MGH, Harvard Medical School