[PATCH libinput 01/10] Replace pointer acceleration with a much simpler linear one

[Steven Newbury]

On Fri, 2014-09-19 at 15:44 +1000, Peter Hutterer wrote:
> We ran a userstudy, evaluating three different accel methods. 
> Detailed results are
> available at:

> http://www.who-t.net/publications/hutterer2014_libinput_ptraccel_study.pdf
> 
> We found that there was little difference between the method we had 
> in
> libinput 0.6 and this three-line function. Users didn't really 
> notice a
> difference, but measured data suggests that it has slight advantages 
> in some
> use-cases.
> 
> The method proposed here is the one labeled "linear" in the paper, 
> its profile
> looks roughly like this:
> 
>         _____________
>        /
>   ____/
>  /
> /
> 
> where the x axis is the speed, y is the acceleration factor.
> The first plateau is at the acceleration factor 1 (i.e. unaccelerated
> movement), the second plateau is at the max acceleration factor. The 
> threshold
> in the code defines where and how long the plateau is.
> 
> Differences to the previous accel function:
> - both inclines are linear rather than curved
> - the second incline is less steep than the current method
> 
> From a maintainer's point-of-view, this function is significantly 
> easier to
> understand and manipulate than the previous one.
> 
Hi Peter,
I'm going to read the report, but I would like to just state my 
initial feeling on this.  Right now, in my experience*, the pointer 
acceleration in libinput/weston is inferior** to that currently in 
Xorg.  I find it relatively difficult to accurately position the 
pointer in Weston while at the same time being able to comfortably 
move the pointer over larger distances in a predictable manner.  The 
Xorg code has been very well tuned over the last few years and IMHO is 
at least as good as the Windows implementation (from a user point of 
view).

Any comparison between the libinput/weston implementations needs to be 
base-lined against current Xorg and Windows/OSX!  I'm certainly not 
opposed to improvements!

Maybe my concerns are unfounded, I'll have a read of the report now... 
:-)

* Using a Synaptics touchpad

** For all I know it's the same code (haven't checked) but the 
parameters must be different or there's a bug somewhere.

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