[RFC libinput] Add dial input device support

[Peter Hutterer]

On Fri, Feb 19, 2016 at 08:03:52PM +0530, PrasannaKumar Muralidharan wrote:
> > right. the approach we used for this was to have an API that exports the
> > value in degrees and an API for get_value_discrete() or similarly named.
> > Look up the libinput_event_pointer*axis* API to get an idea.
> 
> For several devices (example dimmers used for controlling lamps) value
> in degrees is not useful. Exported value depends on device.

remember that libinput is a low-level library and doesn't know about how a
specific device is being used by the layers above it. Hence a value in
degrees isn't any less useful than a value in miscellaneous units which is
what the _discrete() API bit is for. If the caller cares about units, it
uses discrete steps, if it cares about number of rotations, it uses
degrees.

The only requirement in libinput is that you have a units -> physical
degrees mapping which is something we used the hwdb for (in the case of
mouse wheels anyway).

Cheers,
   Peter