[Bf-committers] > Undo system design

[Goran Kocov]

Hi! 

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

> Hi,
> 
> Sorry for the hijacked thread. Hopefully this one
> goes better now.

Don't worry, it's not a big deal. In any case, thanks
for the concern. 
 
> Doing separate stacks for vertex painting - for
> example - would also be  
> impossible to maintain when (amount of) vertices
> change during  
> modeling...

As you mentioned with the potential vertex painting
problem, designing the system so that there's only one
undo stack for a given dataset would be of absolute
highest importance (in your example, the vertex colors
are a part of the mesh object's dataset, so they
should be controled by the mesh object's undo stack
available both from editmode and vertex paint mode
(and possibly UV/Image editor and UV face select
mode)). Having two stacks for one dataset would lead
to all sort of trouble (although I don't know if it's
possible to avoid this with the current architecture).


> It *is* interesting though, and the current editmode
> undo is sort-of  
> non linear now. What I could do - for example - is
> make sure there's  
> some tags in the global undo system that makes sure
> global undo  
> stepping also matches editmode undo state. Like for
> this case;
> 
> 1- Add cube, model it into a plane. exit edit mode
> 2- move it a bit around
> 3- enter editmode, make the plane an ufo. exit
> editmode
> 
> Now if you 'global undo' back to step 2) the
> editmode undo stack also  
> should rewind... if that's possible, since that
> stack of course can be  
> full.
 
If I understood you correctly, in your example "global
undoing" to step 2 would also convert the UFO back to
a plane, right? Well, my idea is exactly the opposite.
At the moment, doing a global undo in Blender also
steps through the editmode stack (enter editmode, make
changes, exit editmode, ctrl+z and the editmode
changes would be reverted). Editmode undo *should* be
independent from global undo. I suppose it would need
some getting used to, but it would provide more
flexibility then a linear undo system. 

Although there's a growing concern in me that this
non-linear undo system would hinder Blender's
workflow. Maybe a linear undo system *is* a better
solution if not more flexible, exactly because of it's
simplicity - you always now what you're going to get. 

O.K. It's late, I'm very tired and I feel I'm going to
start talking nonsense, so before doing that I'm off
to bed :)

Good night everybody,

Goran

> 
> On 17 Nov, 2004, at 21:43, Goran Kocov wrote:
> 
> > 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
> 
=== message truncated ===



		
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