libinput/doc/palm-detection.dox

/**
@page palm_detection Palm detection

Palm detection tries to identify accidental touches while typing.

On most laptops typing on the keyboard generates accidental touches on the
touchpad with the palm (usually the area below the thumb). This can lead to
cursor jumps or accidental clicks.

Interference from a palm depends on the size of the touchpad and the position
of the user's hand. Data from touchpads showed that almost all palm events on a
Lenovo T440 happened in the left-most and right-most 5% of the touchpad. The
T440 series has one of the largest touchpads, other touchpads are less
affected by palm touches.

@section palm_exclusion_zones Palm exclusion zones

libinput enables palm detection on the edge of the touchpad. Two exclusion
zones are defined  on the left and right edge of the touchpad.
If a touch starts in the exclusion zone, it is considered a palm and the
touch point is ignored. However, for fast cursor movements across the
screen, it is common for a finger to start inside an exclusion zone and move
rapidly across the touchpad. libinput detects such movements and avoids palm
detection on such touch sequences.

Each exclusion zone is divided into a top part and a bottom part. A touch
starting in the top part of the exclusion zone does not trigger a
tap (see @ref tapping).

In the diagram below, the exclusion zones are painted red.
Touch 'A' starts inside the exclusion zone and moves
almost vertically. It is considered a palm and ignored for cursor movement,
despite moving out of the exclusion zone.

Touch 'B' starts inside the exclusion zone but moves horizontally out of the
zone. It is considered a valid touch and controls the cursor.

Touch 'C' occurs in the top part of the exclusion zone. Despite being a
tapping motion, it does not generate an emulated button event. Touch 'D'
likewise occurs within the exclusion zone but in the bottom half. libinput
will generate a button event for this touch.

@image html palm-detection.svg

@section trackpoint-disabling Palm detection during trackpoint use

If a device provides a <a
href="http://en.wikipedia.org/wiki/Pointing_stick">trackpoint</a>, it is
usually located above the touchpad. This increases the likelyhood of
accidental touches whenever the trackpoint is used.

libinput disables the touchpad whenver it detects trackpoint activity for a
certain timeout until after trackpoint activity stops. Touches generated
during this timeout will not move the pointer, and touches started during
this timeout will likewise not move the pointer (allowing for a user to rest
the palm on the touchpad while using the trackstick).
If the touchpad is disabled, the @ref t440_support "top software buttons"
remain enabled.


*/