[digikam] [Bug 375573] Don't reset/destroy context after deleting one image among a set of duplicates

[Dan Dascalescu]

https://bugs.kde.org/show_bug.cgi?id=375573

--- Comment #2 from Dan Dascalescu <ddascalescu+kde at gmail.com> ---
Hey Mario,

Thank you for the explanation. I understand the tradeoff - accuracy in
reporting the number of dupes, vs. speedy processing. The solution I propose
revolved around lazy calculation - does the user care more about a precise
number shown next to the album *when they get to see it*, or to be able to move
on to examine the other duplicates in the cluster?

I mentioned "when they get to see it" because after the user deletes one of the
duplicates, the list of duplicate clusters in the left pane always scrolls to
the top (IMO this could be improved to try to keep the scroll position, but
digiKam probably just re-sorts the list), so if they were working on a
duplicate cluster below the fold (i.e. if they have scrolled down at all), the
number of duplicates in that album won't be visible anyway. In fact, when you
deal with many clusters of duplicates, only those items at the top, according
to the sort order (Ref. images filename, # of items, or Avg. similarity) will
be visible.

Not sure what you meant by "one duplicates album" (needs to be adjusted) - did
you mean a cluster (in DUFF terminology, http://duff.dreda.org/) of duplicates
(which may be spread across different albums), or an album that contains
duplicates, so the count of items in the album needs to be adjusted? In the
latter case, that count is even farther from the user's attention, because the
user is in the Fuzzy tab, vs. in the Albums tab. Could the recalculation of
counts be done only once, when the user leaves the Fuzzy tab?

Also, there are two different scenarios I see when it comes to deleting
duplicates:

1) Deleting images in duplicate clusters one by one, while the user looks at
the picture in Preview Mode, to examine it in as large of a size as possible.
In this case, only one image is deleted at a time. Would counts be easier to
decrement in this case?

2) Staying in Thumbnails or Table, selecting multiple images, and deleting them
at once.

Finally, question about "the deleted image may be member of other duplicates
albums" (this relates to the cluster vs. album distinction) - is the duplicate
relationship transitive? I mean, if images A and B are dupes within the
similarity range, and B is part of another cluster of duplicates, A should be
part of that cluster too, which means only two counts need to be updates: the
number of dupes in that cluster, and the number of items in the album the image
belongs to.

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