threads and graphics

[Scott Christley]

Hello,

I seem to remember this working before but maybe my memory is hazy.  If 
I have a thread which is performing some background calculations and it 
attempts to lockFocus on a view to do some drawing then I get a seg 
fault.  After some browsing around it seems that the graphics routines 
rely upon the current thread to store some state data, so obviously 
that data is not present with the background thread.  Does anybody have 
a suggestion on how to handle this?

My application has the standard Model-View-Controller design, and the 
model is a complicated simulation which will be run in a separate 
thread.  The idea being that the GUI is still responsive to the user 
while the simulation is running, and state changes within the 
simulation are reflected to the user through various graphical 
displays.  Now I can conceptualize how to split the work; the View has 
to do all of the drawing in the main thread, yet it is the Model which 
knows when its state has changed and thus knows when the graphical 
displays need to be updated.  However the Model cannot call the View 
directly to do the update because it is running in the wrong thread.  
The Model needs to 'signal' the main thread in some way so that the 
View can do the update.  The difficulty I have with the signaling 
concept is that the Model is composed of many pieces, so a state change 
to one piece would only entail a small change to the graphic display; I 
don't want to use a generic signal which updates all of the graphical 
displays.  This seems to imply that I would have to design an elaborate 
set of signals to get the granularity of display change that I desire; 
something that I don't really want to do.  Hopefully somebody has a 
better idea?

Please send email to me directly as I am not on the list.

thanks
Scott