[Sugar-devel] Is there a way to purposefully do synchronous GUI updates?

[Ajay Garg]

Benjamin,

Thanks for the reply.


On Tue, Aug 21, 2012 at 12:35 PM, Benjamin Berg <benzea at sugarlabs.org>wrote:

> On Tue, 2012-08-21 at 12:18 +0530, Ajay Garg wrote:
> > I am wanting to solve an issue, which in the present case seems
> > possible ONLY by using two threads.
>
> Adding threads into the mix would not help you with your issue
> (threading support in GTK+ is currently being deprecated for good
> reasons, so then you can only do GTK+ calls from the main thread).
>
> In the normal case, when the GUI is updated a queue_draw() is done. The
> corresponding expose events are only fired when the main loop is
> executed, ie. when your function returns.
>
> I think what you are searching for right now is the the process_updates
> function of GdkWindow. This does exactly what you are requesting.



A straightforward query here (sorry for my limited knowledge) ::

Does calling "process_updates" causes the GUI updates to take place, before
the user returns from the function?
That is, will the following scenario necessarily happen ::

                       logic statement 1
                       update GUI
                       process_updates  ===> causes the GUI update
                       logic statement 2  ===> necessarily after GUI update



I doubt that the above is a guarantee, as you have already mentioned that
the actual GUI processing will take place  whenever X server sees it fit.
Anyhow, just wish to confirm :)


Thanks and Regards,
Ajay


> Please
> note that you don't have much control here, you don't know how fast the
> update will happen, or even if it is ever visible to the user. The X
> server will process the drawing commands when it sees fit.
>
> > My intention is to somehow have GUI updates in a synchronous manner,
> > and not rely upon "gobject.idle_add", which would have to have
> > dividing a long workflow into many sub-parts, and chaining these
> > sub-parts through "gobject.idle_add".
> > This is EXTREMELY painful, especially when one needs to do it on an
> > already existing codebase.
>
> As an alternative you could do something like:
>
> def idle_add_function(pos):
>     if pos[0] == 1:
>         # logic 1
>     elif pos[0] == 2:
>         # logic 2
>     else:
>         return False
>
>     queue_update()
>
>     pos[0] += 1
>     return True
>
> Where pos = [0] to begin with (the usage of the list is just so that it
> is global in a way, any object will do, it just needs to be something
> permuteable).
>
> Benjamin
>
>
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