[PATCH weston 4/8] shell: Update bindings to conform to pointer axis protocol

Scott Moreau oreaus at gmail.com
Sat Sep 29 03:01:04 PDT 2012

> Ok, so what I'm trying to do is to enable what people call "smooth
> scrolling" on an input level, meaning that scrolling is not based on
> discrete arbitrary "steps" but on a more fluid motion. These types of
> events makes most sense for certain types of step-less scroll wheels
> and touchpads and I'll try to explain why.
> When axis events are discrete steps, there is indeed little need to
> relate to any kind of coordinate space except knowing what is "up" and
> what is "down". A step can only be 1 or -1, thats it. This is how it
> traditionally works in X11 (except XI2 I think supports non-discrete
> axis events).
> If one wants to have axis events that more resemble smooth motions,
> such as the ones emitted by those step-less scroll wheels or
> touchpads, one needs to specify what the events actually mean, since
> they are no longer only limited to 1 and -1. To do this, if we specify
> an axis event to be a vector along an axis in a coordinate space
> identical to motion events, we can create axis events that relate to
> some measurement already known to both the compositor and client. A
> step-less scroll wheel would transform its scroll events to a motion
> vector measured in pixels and a touchpad would simply emit an axis
> event as it would emit a motion event when scrolling. A client could
> then read these events and can scroll its view by that amount of
> pixels specified by the value parameter.
> Jonas

This makes it much clearer. I saw there was some discussion in IRC a few
days ago too. Perhaps you could put the key points you've made here, in the
protocol description. I guess the only thing is now, evdev needs fixing to
emit the same expected format.

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