[Bf-committers] Undo system design

[Goran Kocov]

Well maybe "unified undo stack" or "unified linear
undo system" would have been better terms, since a
stack is always linear :), but what I ment was an undo
system of the type that's most commonly used in
today's applications - one stack into which all (or
nearly all) changes in the application state are
pushed for later retrieval in case the user needs to
go one or several steps back. 

Now, a "non-linear undo system" would have separate
stacks for different elements of the application
leading to a better flexibility with the cost of a bit
more complicated workflow (i.e. the user has to be
aware when he/she is using which undo stack). Elements
in which complex or sensitive datasets are handled (by
sensitive I mean data in which problems can be
generaly hard to spot) would benefit the most from
local undo stacks since they are most susceptible to
hard-to-correct problems. 

In the case of Blender, one possible implementation
would be:
- one global undo stack per scene (3D Object Mode and
all other modes/editors that are not mentioned for the
local stacks);
- one local stack per object for local object/geometry
changes of meshes, curves, surfaces, metas, lattices
and armatures (3D Edit Mode, Weight Paint, Vertex
Paint, Pose Mode); 
- one local stack for UV mapping (per mesh object) and
texture painting (UV Face Select, UV/Image Editor,
Texture Paint (maybe the texture painting part should
be transfered to the global stack, since it's not
directly related to an object));
- one stack (per object if it's object data that's
handled) for animation (IPO Editor, Action Editor, NLA
Editor (although the NLA would be tricky, since it
functions globaly));
- one local stack for each script in the text editor;
- one local stack for the sequence editor; 

I'm aware that there are a lot of
problems/inconsistencies to solve (especially where
editors with different undo stacks can operate on the
same dataset), but this is still heavily WIP and I
think that with some effort the non-linear undo system
can lead to a very effective undo solution. 

Please, have in mind that I haven't spent a lot of
time/energy in coming up with this proposal, so some
parts are probably confusing and/or inconsistent. 

Thanks,
Goran

P.S. Guys, please don't take over my thread or at
least change the subject name. 

--- Ton Roosendaal <ton at blender.org> wrote:

> Hi,
> 
> No, this is the proper maillist for such
> discussions. :)
> 
> I've never really investigated what 'proper' undo
> architectures are, so  
> your remarks on 'unified linear undo stack' I don't
> really get... what  
> would 'non-linear' undo be?
> 
> My remark in the release notes on the current undo
> issues are more from  
> a user perspective, with multiple different undo
> systems being in use  
> now (editmode undo versus global undo). This can
> lead to confusement,  
> and it is worth trying to unify I think.
> 
> The current undo system does indeed include more
> features we can add  
> for a next release yes. The full undo stack can just
> be written in  
> files. Or even better, I thought of dumping the
> entire undo stack  
> including current project on exit, and just have it
> read back on  
> restart of Blender. Would be a very interesting
> experiment, and  
> certainly be extremely cool to show off. :)
> 
> Whether Blender has a 'farsighted design' opinons
> can differ though,  
> I'm usually quite humble about that. But for
> presentation/marketing of  
> our project it wouldn't hurt to emphasise some more
> of the good things  
> in Blender, so a text as you wrote below should be
> at least quoted on  
> our blender3d.org website!
> 
> -Ton-
> 
> 
> On 17 Nov, 2004, at 13:09, Goran Kocov wrote:
> 
> > Hi!
> >
> > While browsing through the 2.35 changes documents
> > yesterday, I noticed that the undo system design
> is
> > still not completly resolved and that there's a
> > possibility of switching to a unified linear undo
> > stack.
> >
> > Since in many design decisions, Blender has proven
> to
> > be years ahead compared to other 3D apps (excelent
> > example is the UI with the non-overlaping windows,
> the
> > widgetless transforms, etc. resulting in a nearly
> > unsurpassed workflow), I see the flexible and
> elegant
> > solution of a non-linear undo system (which is, in
> a
> > large part, already implemented) as a possibility
> once
> > again to show the 3D world the farsightedness of
> > Blender's design.
> >
> > I'm not very familiar with Blender's architecture,
> so
> > I can't tell the possible technical pitfalls of
> this
> > approach, but IMO, from a design point-of-view,
> going
> > to a unified undo system would be a *bad*
> decision.
> >
> > Another very useful undo related feature would be
> the
> > capability to save the undo stacks in the blend
> > project file, thus enabling the user to undo
> changes
> > even after the project has been closed and then
> > reloaded. Once again, I don't know if this is
> possible
> > and/or practical with the current architecture (I
> > suppose the size of the project file would rise
> > exponentially with the undo stacks included, but I
> > can't see any other problems at the moment).
> >
> > Goran
> >
> > P.S. If the right place for this post is in the
> > functionality board mailing list, please tell me
> and
> > I'll move the thread there.
> >
> >
> >
> > 		
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> >
> >
>
------------------------------------------------------------------------
> 
> --
> Ton Roosendaal  Blender Foundation ton at blender.org  
> http://www.blender.org
> 
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