Communicate scroll inversion/natural scrolling flag to clients
"Natural scrolling" is intended to convey a change in scrolling behavior from scrollbar/viewport-centric to content-centric. Typically, this is implemented by globally inverting the scroll Y direction, which was traditionally defined the other way around.
However, this doesn't work for scroll actions where there is no viewport. There, the existing behavior is already "natural". Therefore, even if scroll direction is inverted globally at the compositor/input layer, clients need to be told about this so they can choose whether to invert it again where necessary.
On macOS, this was accomplished by tagging scroll events with an isDirectionInvertedFromDevice
flag. Qt implements this and therefore everything works as expected on macOS. On Wayland, Qt just always takes this flag as false, and this results in unexpected behavior for clients [1] [2] [3] etc.
There was an attempt to add this back in 2017, but it went nowhere. I think we should move forward with this, as more and more users are expecting natural scrolling on their machines.