Trackpoints and Pointing Sticks
This page provides an overview of trackpoint handling in libinput, also referred to as Pointing Stick or Trackstick. The device itself is usually a round plastic stick between the G, H and B keys with a set of buttons below the space bar.
libinput always treats the buttons below the space bar as the buttons that belong to the trackpoint even on the few laptops where the buttons are not physically wired to the trackpoint device anyway, see Lenovo *40 series touchpad support.
Motion range on trackpoints
It is difficult to associate motion on a trackpoint with a physical reference. Unlike mice or touchpads where the motion can be measured in mm, the trackpoint only responds to pressure. Without special equipment it is impossible to measure identical pressure values across multiple laptops.
The values provided by a trackpoint are motion deltas, usually corresponding to the pressure applied to the trackstick. For example, pressure towards the screen on a laptop provides negative y deltas. The reporting rate increases as the pressure increases and once events are reported at the maximum rate, the delta values increase. The figure below shows a rough illustration of this concept. As the pressure decreases, the delta decrease first, then the reporting rate until the trackpoint is in a neutral state and no events are reported. Trackpoint data is hard to generalize, see Observations on trackpoint input data for more details.
The delta range itself can vary greatly between laptops, some devices send a maximum delta value of 30, others can go beyond 100. However, the useful delta range is a fraction of the maximum range. It is uncomfortable to exert sufficient pressure to even get close to the maximum ranges.
libinput provides a Magic Trackpoint Multiplier to normalize the trackpoint input data.