File Display Modes -> Thumbnails -> Display Thumbnails For Folders is checked
File Display Modes -> Thumbnails -> Adjust Folder Thumbnail Settings is set to: Generate Folder Thumbnail From Images Inside Folder
so I have some kind of preview what's inside the folder.
Now, let's say I changed some pics inside and I would like the folder thumbnail to be updated accordingly. How to achieve that?
I'm translating into polish an old Amiga game called Biing. Having these folder thumbs updated would speed up the process a lot (because I can see just by looking at the thumb which folders are already done).
F5 refresh (or re-visiting the folder) updates them OK here.
Does clearing the thumbnail cache update them for you? If not, maybe the problem is something different. (e.g. If you're expecting it to find images in folders recursively, it won't do that; only images directly below each folder.)
I just found the reason - why I didn't think of it before...
I change/translate the pictures in GIMP and then use OVERWRITE (in GIMP).
Opus changes thumbnail responsible for that picture but it doesn't update folder's thumbnail (even F5 or re-visiting the folder doesn't help here).
Only when I remove or add a picture to the folder then the folder's thumbnail gets updated.
That makes sense. We probably only update the folder's thumbnail if the folder's Modified timestamp changes, which happens if a file in the folder is added or removed, but not if one is overwritten in-place (without deleting the old one and creating a new one, which some programs will do).
If the folder's timestamp has not changed, the only way to know if there are any new/changed files is to list the whole folder, which can cause unwanted disk access.
Disabling thumbnail caching while working on the project is one option, but will of course mean you get that extra disk access and thumbnail calculation every time.
A better option, perhaps, is to make a button or hotkey which runs Go REFRESHTHUMBS which should let you regenerate thumbnails for the current folder without clearing the cache for everywhere else. (You could add that to the F5 hotkey if you wanted to do it all the time.)