[WebODF] Undo/redo actions

[Friedrich W. H. Kossebau]

Hi Philip,

no time for detailed reply today, but definitely interesting topic, which can 
be seen already to sit & wait directly on our way into the future :)

Am Mittwoch, 31. Juli 2013, 04:28:23 schrieb Philip Peitsch:
> Hi everybody,
> 
> I've been considering the following thought experiment for undo/redo:
> 
> 1. Doc state = A
> 2. Op A is performed by Mandy, Doc state = B
> 3. Op B is performed by Fred, Doc state = C
> 4. Mandy hits undo on her local editor
> 5. Doc state = ??
> 
> What does Mandy expect to have happen? Does this undo Op A or Op B?

Another option would be to just have Undo to be another new operation which 
just is the invert of the op that should be undone. Which means the original 
op will stay part of the op stack, and "just" a new one is added on top. Then 
no special handling of ops is needed, and transformation can be done as 
before.
It might be also possible to undo any op in the stack (given the inverted op 
can be transformed through the rest of the op stack). So the UI could offer to 
just undo your own last ops, or undo ops/actions from everyone.

Would also mean no need for the complexity of a dedicated undo/redo manager. 
But also means that your accidental paste of a private message to your better 
half will also after "undo!!!" stay in the op history, uh :) (though doing 
deletion surgery on the op stack could be another future feature to have)

Of course this requires that all info needed to invert an operation is still 
available, like the properties of removed styles, overwritten style 
properties, removed text, etc. Which means quite some changes to our current 
opspecs and op creation code, but this should not stop us, at least in the 
long run.

In any case we should see to keep clients ODTs as convergent as possible, 
ideally 100 %. Anything else might only mean troubles later and hard to 
reproduce errors, my gut tells.

Cheers
Friedrich
-- 
Friedrich W. H. Kossebau // KO GmbH
http://kogmbh.com/legal/