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Some files had pre-commit style issues. Fix them. Signed-off-by: José Expósito <jose.exposito89@gmail.com> Part-of: <https://gitlab.freedesktop.org/libinput/libinput/-/merge_requests/1036>
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.. _touchpad_pressure:
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==============================================================================
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Touchpad pressure-based touch detection
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==============================================================================
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libinput uses the touchpad pressure values and/or touch size values to
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detect whether a finger has been placed on the touchpad. This is
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:ref:`kernel_pressure_information` and combines with a libinput-specific hardware
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database to adjust the thresholds on a per-device basis. libinput uses
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these thresholds primarily to filter out accidental light touches but
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the information is also used for some :ref:`palm_detection`.
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Most devices only support one of either touch pressure or touch size.
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libinput uses whichever is available but a preference is given to touch size
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as it provides more specific information. Since most devices only provide
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one type anyway, this internal preference does not usually matter.
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Pressure and touch size thresholds are **not** directly configurable by the
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user. Instead, libinput provides these thresholds for each device where
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necessary. See :ref:`touchpad_pressure_hwdb` for instructions on how to adjust
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the pressure ranges and :ref:`touchpad_touch_size_hwdb` for instructions on
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how to adjust the touch size ranges.
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.. _kernel_pressure_information:
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------------------------------------------------------------------------------
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Information provided by the kernel
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------------------------------------------------------------------------------
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The kernel sends multiple values to inform userspace about a finger touching
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the touchpad. The most basic is the ``EV_KEY/BTN_TOUCH`` boolean event
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that simply announces physical contact with the touchpad. The decision when
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this event is sent is usually made by the kernel driver and may depend on
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device-specific thresholds. These thresholds are transparent to userspace
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and cannot be modified. On touchpads where pressure or touch size is not
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available, libinput uses ``BTN_TOUCH`` to determine when a finger is
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logically down.
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Many contemporary touchpad devices provide an absolute pressure axis in
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addition to ``BTN_TOUCH``. This pressure generally increases as the pressure
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increases, however few touchpads are capable of detecting true pressure. The
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pressure value is usually related to the covered area - as the pressure
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increases a finger flattens and thus covers a larger area. The range
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provided by the kernel is not mapped to a specific physical range and
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often requires adjustment. Pressure is sent by the ``ABS_PRESSURE`` axis
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for single-touch touchpads or ``ABS_MT_PRESSURE`` on multi-touch capable
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touchpads. Some devices can detect multiple fingers but only provide
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``ABS_PRESSURE``.
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Some devices provide additional touch size information through
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the ``ABS_MT_TOUCH_MAJOR/ABS_MT_TOUCH_MINOR`` axes and/or
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the ``ABS_MT_WIDTH_MAJOR/ABS_MT_WIDTH_MINOR`` axes. These axes specifcy
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the size of the touch ellipse. While the kernel documentation specifies how
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these axes are supposed to be mapped, few devices forward reliable
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information. libinput uses these values together with a device-specific
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:ref:`device-quirks` entry. In other words, touch size detection does not work
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unless a device quirk is present for the device.
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