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doc: expand trackpoint pointer acceleration documentation a bit

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Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
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Peter Hutterer 2016-11-03 14:01:17 +10:00
parent 76008034ca
commit e0ccfc87f0
1 changed files with 22 additions and 3 deletions
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doc/pointer-acceleration.dox
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@ -108,14 +108,33 @@ The image above shows the touchpad acceleration profile in comparison to the
@section ptraccel-trackpoint Pointer acceleration on trackpoints
Trackpoint hardware is quite varied in how it reacts to user pressure and
unlike other devices it cannot easily be normalized for physical properties.
Measuring pressure objectively across a variety of hardware is nontrivial.
libinput relies on some sytem-wide configured properties, specifically the
@ref udev_config. The two properties that influence trackpoint acceleration
````POINTINGSTICK_CONST_ACCEL```` which is a constant factor applied to the
trackpoint's motion data. For example, a factor of 3 will see all input data
multipled by 3. This multiplication is done by libinput.
Additionally, some trackpoints provide the ability to adjust the sensitivity in
hardware by modifying a sysfs file on the serio node. The udev property
````POINTINGSTICK_SENSITIVITY```` indicates the desired value, a udev
builtin is expected to apply this to the device, i.e. libinput does not
handle this property. Once applied, the sensitivity adjusts the deltas
coming out of the hardware.
Trackpoint pointer acceleration uses the @ref ptraccel-low-dpi profile, with a
constant deceleration factor taking the place of the DPI settings.
constant acceleration factor taking the place of the DPI settings.
@image html ptraccel-trackpoint.svg "Pointer acceleration curves for trackpoints"
The image above shows the trackpoint acceleration profile in comparison to the
@ref ptraccel-linear. The constant acceleration factor, usually applied by
udev, shapes the acceleration profile.
@ref ptraccel-linear.
The constant acceleration factor, usually applied in
@ref udev_config, shapes the acceleration profile and is pre-applied before
any user-specific acceleration adjustments.
@section ptraccel-profile-flat The flat pointer acceleration profile