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RedBear-OS/local/recipes/libs/libinput/source/doc/user/touchpad-thumb-detection.rst
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vasilito f31522130f fix: comprehensive boot warnings and exceptions — fixable silenced, unfixable diagnosed
Build system (5 gaps hardened):
- COOKBOOK_OFFLINE defaults to true (fork-mode)
- normalize_patch handles diff -ruN format
- New 'repo validate-patches' command (25/25 relibc patches)
- 14 patched Qt/Wayland/display recipes added to protected list
- relibc archive regenerated with current patch chain

Boot fixes (fixable):
- Full ISO EFI partition: 16 MiB → 1 MiB (matches mini, BIOS hardcoded 2 MiB offset)
- D-Bus system bus: absolute /usr/bin/dbus-daemon path (was skipped)
- redbear-sessiond: absolute /usr/bin/redbear-sessiond path (was skipped)
- daemon framework: silenced spurious INIT_NOTIFY warnings for oneshot_async services (P0-daemon-silence-init-notify.patch)
- udev-shim: demoted INIT_NOTIFY warning to INFO (expected for oneshot_async)
- relibc: comprehensive named semaphores (sem_open/close/unlink) replacing upstream todo!() stubs
- greeterd: Wayland socket timeout 15s → 30s (compositor DRM wait)
- greeter-ui: built and linked (header guard unification, sem_compat stubs removed)
- mc: un-ignored in both configs, fixed glib/libiconv/pcre2 transitive deps
- greeter config: removed stale keymapd dependency from display/greeter services
- prefix toolchain: relibc headers synced, _RELIBC_STDLIB_H guard unified

Unfixable (diagnosed, upstream):
- i2c-hidd: abort on no-I2C-hardware (QEMU) — process::exit → relibc abort
- kded6/greeter-ui: page fault 0x8 — Qt library null deref
- Thread panics fd != -1 — Rust std library on Redox
- DHCP timeout / eth0 MAC — QEMU user-mode networking
- hwrngd/thermald — no hardware RNG/thermal in VM
- live preload allocation — BIOS memory fragmentation, continues on demand
2026-05-05 20:20:37 +01:00

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.. _thumb_detection:
==============================================================================
Thumb detection
==============================================================================
Thumb detection tries to identify touches triggered by a thumb rather than a
pointer-moving finger. This is necessary on :ref:`touchpads_buttons_clickpads`
as a finger pressing a button always creates a new touch, causing
misinterpretation of gestures. Click-and-drag with two fingers (one holding
the button, one moving) would be interpreted as two-finger scrolling without
working thumb detection.
libinput has built-in thumb detection, partially dependent on
hardware-specific capabilities.
- :ref:`thumb_pressure`
- :ref:`thumb_areas`
- :ref:`thumb_speed`
Thumb detection uses multiple approaches and the final decision on whether
to ignore a thumb depends on the interaction at the time.
.. _thumb_pressure:
------------------------------------------------------------------------------
Thumb detection based on pressure or size
------------------------------------------------------------------------------
The simplest form of thumb detection identifies a touch as thumb when the
pressure value goes above a certain threshold. This threshold is usually
high enough that it cannot be triggered by a finger movement.
On touchpads that support the ``ABS_MT_TOUCH_MAJOR`` axes, libinput can perform
thumb detection based on the size of the touch ellipse. This works similar to
the pressure-based palm detection in that a touch is labelled as palm when
it exceeds the (device-specific) touch size threshold.
Pressure- and size-based thumb detection depends on the location of the
thumb and usually only applies within the :ref:`thumb_areas`.
For some information on how to detect pressure on a touch and debug the
pressure ranges, see :ref:`touchpad_pressure`. Pressure- and size-based
thumb detection require thresholds set in the :ref:`device-quirks`.
.. _thumb_areas:
------------------------------------------------------------------------------
Thumb detection areas
------------------------------------------------------------------------------
Pressure and size readings are unreliable at the far bottom of the touchpad.
A thumb hanging mostly off the touchpad will have a small surface area.
libinput has a definitive thumb zone where any touch is considered a
thumb. Immediately above that area is the area where libinput will label a
thumb as such if the pressure or size thresholds are exceeded.
.. figure:: thumb-detection.svg
:align: center
The picture above shows the two detection areas. In the larger (light red)
area, a touch is labelled as thumb when it exceeds a device-specific
pressure threshold. In the lower (dark red) area, a touch is always labelled
as thumb.
Moving outside the areas generally releases the thumb from being a thumb.
.. _thumb_speed:
------------------------------------------------------------------------------
Thumb movement based on speed
------------------------------------------------------------------------------
Regular interactions with thumbs do not usually move the thumb. When fingers
are moving across the touchpad and a thumb is dropped, this can cause
erroneous scroll motion or similar issues. libinput observes the finger
motion speed for all touches - where a finger has been moving a newly
dropped finger is more likely to be labeled as thumb.
------------------------------------------------------------------------------
Thumb detection based on finger positions
------------------------------------------------------------------------------
The shape of the human hand and the interactions that usually involve a
thumb imply that a thumb is situated in a specific position relative to
other fingers (usually to the side and below). This is used by libinput to
detect thumbs during some interactions that do not implicitly require a
thumb (e.g. pinch-and-rotate).