I have thought about it and played around with GTK 3 a few times, but due to the amount of changes in GTK 3 the task to upgrade the codebase is pretty significant - I do not have that kind of time on my hands. If I am to write a GTK 3 or 4 version of Viewnior, I will also likely switch to a different language - more or less starting from the ground up.

I work on it for some time and struggle with porting drawing from GDK to cairo. Everything other is quite straightforward.

I've got an old port of Viewnior 1.1 to GTK3 with everything working, including migration from GDK drawing to cairo.

I can clean it up a bit, rebase and make a pull request.

Hopefully the developer finds the time to update the app. It is by far the fastest and simplest app out there to just open images and I miss it dearly :(