[Bf-committers] Global undo & running python scripts

[joeedh]

Jonathan Merritt wrote:

> Campbell Barton wrote:
>
>> Ton Roosendaal wrote:
>>
>>> A related issue was reported in the tracker about running python  
>>> scripts (with GUI). Can one of our python team members say 
>>> something  about the correct circumstances to detect whether a 
>>> running script can  be closed and safely restarted after Undo?
>>>
>>> -Ton-
>>
>>
>> I dont know if its reasionable to ask- but would it be possible not 
>> to exit the script at all? At the moment undo takes long enough with 
>> large files, re-running all scripts would not make things any faster.
>> But this could be a stop gap solution... :)
>> - Cam
>
>
>
> Commenting purely on some of my own scripts...
>
> I have several scripts (in the Blix distribution) which run "in 
> parallel" with the rest of Blender.  They rely on being able to detect 
> "changes" in the rest of Blender.  The main example of this is changes 
> to the current selection.  Currently, I detect when the current 
> selection has changed using a rather crazy hack: I procedurally create 
> a new script (from within the first), attach it to the scene "Redraw" 
> scriptlink, and then have that second script manually redraw the all 
> of the script windows when Blender redraws the scene!  (Yes, it does 
> sound like a lot of work!)  It's completely nuts to have to jump 
> through hoops like this for very simple interaction.
>
> Having the potential for Blender to re-start scripts in some kind of 
> ad-hoc fashion to fit in with the undo system would be a massive 
> spanner in the works.  What I think is needed is a "real" callback API 
> from Blender providing hooks into the undo system and the rest of the 
> GUI.  I would lead the cheer if script links were scrapped forever in 
> favour of a more extensive system.
>
> Such a system could take the form of (for example) a Python class 
> which is passed to Blender by a function when the script is first 
> run.  The class could then override various method callbacks that 
> Blender can natively pump events into.   From the Python side, it 
> would look something like this:
>
> class MyCallbackHandler(Blender.Callback):
>    def selectionChanged(self, ...):
>       """Called when the selection in Blender has changed."""
>
> It would also be possible to define a finer-grained set of callback 
> classes for specific purposes.  The model would follow something 
> similar to Java's "listeners", with perhaps one listener being 
> responsible for the scene, another for objects, another for undo 
> events, another for mesh data, etc...
>
I proposed something very similar to this last year.  My frustration 
with bpython's ability to produce real "plugins" lead me to write the 
(very simple) OnSave scriptlink, and eventually to a version of your idea. 

Anyway, I think your idea is better then mine, and you seemed to have 
developed it into a more logical fashion.

joeedh