Hey,
On Sat, Sep 24, 2016 at 07:23:30PM +0200, Jon Nordby wrote:
> On 10 September 2016 at 23:12, Philip R. Dutton
> wrote:
> > I ran across much talk and some implementation of GEGL. I can see how the
> > Undo /History features would make great use of the DAG graph data structure
> > used by GEGL.
> >
> > Q: How hard will it be to log the GEGL graph evolution to disk in real-time
> > using perhaps a rolling log? What is the best approach for an idea like
> > this?
>
> For the approach, pippin and I sketched together a basic spec a couple
> of years back.
> https://mail.gnome.org/archives/gegl-developer-list/2012-June/msg4.html
> https://git.gnome.org/browse/gegl/tree/docs/journal.txt
>
> [...]
>
> *However*, I believe the GEGL graphs used in GIMP are still "short
> lived" - used for the duration of one operation and then applied
> destructively. Meaning that there is no one graph which represents the
> entire document and thus the evolution of your artwork.
> It may be possible to try to stich together a sort of journal from all
> these , but probably there would be need for a significant amount of
> GIMP specific logic in addition... Not sure of the feasibility here.
Other than what Jon already said, I wanted to point out that if you
ran gnome-photos [*] with G_MESSAGES_DEBUG=all and
GNOME_PHOTOS_DEBUG=gegl, then it logs an XML representation of the
graph whenever something causes it to change. The final graph is
stored persistently (as XML) in ~/.local/share/gnome-photos.
Since the editing UI is relatively simple compared to GIMP, we use
snapshots to undo a whole series of operations, instead of undoing
every single change in the properties. I think this is similar to
transactions in Jon's references. The snapshots are again just XML
in memory.
All this is pretty straightforward in gnome-photos, because, unlike
current GIMP versions, it is structured for non-destructive editing.
Cheers,
Rishi
[*] You'd need at least version 3.20.x.
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