GtkScrollbar horizontal mouse wheel scroll direction is wrong
In a horizontal scrollbar, wheel-up should scroll to the left (the origin of whatever is scrolled) just like scroll-up on a vertical scrollbar scrolls up.
Try this: have any scrolled window with scrollbars, shift-scroll-up on the content scrolls to the left, scroll-up on the scrollbar scrolls to the right.
I tried to figure the invert logic, but it got a lot more complicated since GTK+ 2.x.
Edited by Michael Natterer