My usecases:

1. When looking at similar photos (e.g. a series of 10 pics shot in short time of a group and trying to identify the best to keep with the least amount of closed eyes / open mouths ...) I open my "current favorite" in a new gwenview instance, while I jump back and forth through the remaining 9 pictures. Yes, gwenview has a "side-by-side comparison" for multi-selection, but it cannot navigate the second picture view independently. Moreover I find it easier, to make the computer toggle the image in the same place, instead of me flipping my eyes like in those news-paper-riddles, where you shall find the differences between two photos. Alt+Tab gives me this easily when pressed quick enough to not trigger the animation. Also I know, gwenview can in full screen navigate back and forth through the pictures (one at a time). But it is bound by an order - so to toggle back and forth between the 2nd and 8th picture in the set, I need to symlink them in a temp-folder, which is just too cumbersome.

2. Going through my collection with e.g. the task: symlink all nice pictures of my mother to folder xyz, so I can later present them to her for choosing the one to put on the birthday invitations, I get distracted by "Who's sitting next to her? - Maybe I can find this shirt again on my dads camera ...". For this temporary "side-quest" I open a second gwenview instance to not loose the position on my earlier quest, because I don't want to again flic through the 300+ pictures I already sifted through.

3. Reading a comic strip as a sequence of pictures, you might want to refresh your memory, when there is a back-reference or even, how the character looked like when he showed up last - was he already in the previous installment wearing this long cape? Now, how to keep the current position and at the same time jump around to find the other occurrence for comparison?

To summarize the similarity of those use-cases: The current selection in gwenview is on the one hand very fleeting and easily destroyed information - by just selecting something else. On the other hand, especially in large folders with many pictures, it can be a valuable marker e.g. of progress or a "bookmark" to jump (back) to. While I usually finish with it in a matter of a few minutes, it is not worth the hassle of e.g. taking a note of the filename or symlinking the picture on the Desktop to return to the task tomorrow. So opening a second or third instance of gwenview suits my workflow perfectly.

It's actually quite comparable to browsing on the internet, only that I use full gwenview windows instead of browser tabs to mark certain positions in the picture collection, in time and in progress of a supposed "reading list". Now imagine the outcry, if Firefox removed the "open in new tab" command?

But before someone over-engineers this into a fancy new "annotated image-history", there is not only the image itself to be preserved. In the second example notice the current task comprises also symlinking found pictures to folder xyz  - so you bet, the folder view is open and not the image information and it is scrolled and unfolded appropriately to show xyz as a prominent drop-target. Navigating other folders surely will unfold more "clutter" and shunt xyz out of the way and returning to a bookmarked picture will likely not restore the folder-tree. All this I get for free by opening a second instance.

A possibly relevant merge request was started @ https://invent.kde.org/graphics/gwenview/-/merge_requests/199

Git commit 83dc031b65d3e1406fbb6a5b049b6f32238adc78 by Nate Graham, on behalf of Eugene Popov.
Committed on 16/05/2023 at 17:18.
Pushed by ngraham into branch 'master'.

Add an action to open in a new window

After Bug 462088 was resolved by removing Gwenview from its own "Open With"
menu, it turned out that some people were using this for various workflows.

To support them in a way that doesn't look like a bug to users without
those workflows, this commit adds an action that allows the user to open
the currently selected item or currently viewed image in a new window.
FIXED-IN: 23.08

M  +31   -3    app/fileopscontextmanageritem.cpp
M  +2    -0    app/fileopscontextmanageritem.h
M  +1    -0    app/thumbnailviewhelper.cpp
M  +1    -0    app/viewmainpage.cpp

https://invent.kde.org/graphics/gwenview/commit/83dc031b65d3e1406fbb6a5b049b6f32238adc78

Thanks for the quick reaction. Only I marvel, if this solution doesn't add unnecessary complexity?
- first you filter the "open-with" menu with extra code, that would give us the wanted feature "for free"
- second you re-implement an open in Gwenview somewhere else with extra code.

Haven't seen it in action and don't know jet, how it feels - But there is a chance that it is out of place and users need to tolerate another quirk in the GUI, that Gwenview itself is the only app not showing up in open with, even though it is in open with of Dolphin or others (e.g. Gwenviews own file-open-dialog, that features a rightclick menu with the file-managers open-with instance, right?).

To reconcile me, I hope for a keyboard-shortcut that can be customized to the new command? Sadly, the old open with was hard to reach form the keyboard.

That had actually occurred to me as well, but ultimately I think this solution works acceptably because it makes the intended workflow clear. And yes, the new approach can be customized with a keyboard shortcut to trigger it quickly and easily.