Mouse accelleration needs some tweaking

[Michael Zanetti]

Since the mouse acceleration has been implemented, touch pads have become hard to use because moving the finger very slow causes the mouse cursor to not move at all. Speeding the finger movement up a little bit, makes the mouse cursor move too fast to easily center in on small mouse areas (e.g. window control buttons)

The acceleration should work in a way that the slowest possible finger movement already does move the cursor slowly. Increasing the finger movement speed should then increase the acceleration progressively, and not like at the moment, where there is a jump between not moving at all and moving relatively fast already.

[Daniel van Vugt (vanvugt)]

The "not moving at all" problem is bug 1528109, fixed in Mir 0.22.0.

The remaining issue is that the libinput acceleration curve is subjectively not a pleasant one to use, and the cursor soon (non-linearly) moves too quickly. That's bug 1524145 still open. But the fix for that is simple -- we just need to default to acceleration 'off'. Then the cursor will move exactly like it does in Unity7.

[Daniel van Vugt (vanvugt)]

Attached to bug 1524145 you will find:
  (a) A rejected branch that fixes it; and
  (b) A landed branch that provides options (disabled by default) to fix it.

:)

[Daniel van Vugt (vanvugt)]

Having said that, please check the fix for Unity8 bug 1510382 to make sure it does not regress on the fix for bug 1528109.