We've run into a significant technical hurdle in trying to implement a horizontal scrollbar: The Tk text widget sets the horizontal scroll position only according to the currently visible lines! If the text was scrolled to the right, scrolling down to where there are only shorter lines will scroll the text back to the left!!

Implementing this will require either getting a fix for this into Tk itself, or finding a good workaround.

The workaround I was considering--wrapping the text widget with a frame and implementing custom scrolling logic--is very unlikely to provide reasonable performance with large files. This is because it will have to have all of the text widget rendered at all times, which the Tk Text widget takes special care to avoid in order to achieve good performance.