[PATCH libinput 0/7] tablet: add support for relative x/y motion deltas

[Peter Hutterer]

This patchset adds support for relative motion to the tablet branch. AFAICT,
this is the last large feature that was still missing.
The approach is notably different to the current X driver. There we
toggle a property in the driver to switch the tablet into relative mode and
then only send out relative events. The property works per tool.

libinput's approach is to always calculate relative motion and provide both
absolute and relative motion for each event. The caller must decide which
tool should use which type of motion. 

Unlike the X driver, the relative motion is converted into a pixel-like
motion vector that can be used like the mouse motion. if a caller wants
mm-based movement they can easily calculate the deltas themselves anyway.

Pointer acceleration is quite simple atm, it's a flat profile and the speed
setting simply multiplies the vector. Can be extended later if need be.

Cheers,
  Peter