Comment 3 for bug 1866653

I did some investigation, a virtual comboboxes would help, but it is hiding the root cause:

I traced the code, and have found the following issues:

Most of the time is spent outside of Pinta, but rather in GTK/GTKSharp. It is probably using a sub-optimal path.

The program is running all of this in the UI thread though, and it freezes for the user for over 90 seconds, often timing out and cancelling the operation.