events: Pass through the scroll wheel source when known#15965
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events: Pass through the scroll wheel source when known#15965Kontrabant wants to merge 2 commits into
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If the source of a scroll event is known to be from a finger, pass this information through in the scroll wheel event. Additionally, a scroll event for a finger with a delta of 0,0 may be passed through to indicate that the scroll ended due to the finger being lifted. This allows for implementing client-side kinetic scrolling via a 'flick' gesture.
Use the new information in scroll events to implement kinetic scrolling when finger scroll events are received.
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If the source of a scroll event is known to be from a finger, pass this information through in the scroll wheel event. Additionally, a scroll event with a finger source and a delta of 0,0 may be passed through to indicate that the scroll ended due to the finger being lifted.
This allows for implementing client-side kinetic scrolling via a 'flick' gesture. A basic demonstration of this functionality was added to testmouse.
This information is currently passed through on X11 and Wayland. There is probably a way to get this information on Apple platforms, but I haven't looked into it yet, and Macs have native kinetic scrolling that can be enabled via a hint. No idea about Windows, as kinetic scrolling there seems to be implemented by third-party drivers.
As mentioned, to indicate finger lift, a mouse wheel event with x and y values of 0.0 are sent. It's unlikely that sending zero scroll values would cause problems in existing software, but it is a slight behavior change, so maybe a separate SDL_EVENT_MOUSE_WHEEL_STOP (SDL_EVENT_MOUSE_WHEEL_FINGER_LIFTED?) event would be better suited for this?
Fixes #15955