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8b1141acdc
Only one link leads to it and it doesnt (right now) fit into the hierarchy. Let's get rid of the sphinx warning. Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
225 lines
9.7 KiB
ReStructuredText
225 lines
9.7 KiB
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.. _touchpads:
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==============================================================================
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Touchpads
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==============================================================================
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This page provides an outline of touchpad devices. Touchpads aren't simply
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categorised into a single type, instead they have a set of properties, a
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combination of number of physical buttons, multitouch support abilities and
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other properties.
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.. _touchpads_buttons:
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------------------------------------------------------------------------------
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Number of buttons
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------------------------------------------------------------------------------
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.. _touchapds_buttons_phys:
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..............................................................................
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Physically separate buttons
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..............................................................................
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Touchpads with physical buttons usually provide two buttons, left and right.
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A few touchpads with three buttons exist, and Apple used to have touchpads
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with a single physical buttons until ca 2008. Touchpads with only two
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buttons require the software stack to emulate a middle button. libinput does
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this when both buttons are pressed simultaneously.
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Note that many Lenovo laptops provide a pointing stick above the touchpad.
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This pointing stick has a set of physical buttons just above the touchpad.
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While many users use those as substitute touchpad buttons, they logically
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belong to the pointing stick. The \*40 and \*50 series are an exception here,
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the former had no physical buttons on the touchpad and required the top
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section of the pad to emulate pointing stick buttons, the \*50 series has
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physical buttons but they are wired to the touchpads. The kernel re-routes
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those buttons through the trackstick device. See :ref:`t440_support` for more
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information.
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.. _touchpads_buttons_clickpads:
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..............................................................................
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Clickpads
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..............................................................................
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Clickpads are the most common type of touchpads these days. A Clickpad has
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no separate physical buttons, instead the touchpad itself is clickable as a
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whole, i.e. a user presses down on the touch area and triggers a physical
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click. Clickpads thus only provide a single button, everything else needs to
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be software-emulated. See :ref:`clickpad_softbuttons` for more information.
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Clickpads are labelled by the kernel with the **INPUT_PROP_BUTTONPAD** input
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property.
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.. _touchpads_buttons_forcepads:
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..............................................................................
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Forcepads
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..............................................................................
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Forcepads are Clickpads without a physical button underneath the hardware.
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They provide pressure and may have a vibration element that is
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software-controlled. This element can simulate the feel of a physical
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click or be co-opted for other tasks.
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.. _touchpads_touch:
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------------------------------------------------------------------------------
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Touch capabilities
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------------------------------------------------------------------------------
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Virtually all touchpads available now can **detect** multiple fingers on
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the touchpad, i.e. provide information on how many fingers are on the
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touchpad. The touch capabilities described here specify how many fingers a
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device can **track**, i.e. provide reliable positional information for.
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In the kernel each finger is tracked in a so-called "slot", the number of
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slots thus equals the number of simultaneous touches a device can track.
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.. _touchapds_touch_st:
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..............................................................................
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Single-touch touchpads
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..............................................................................
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Single-finger touchpads can track a single touchpoint. Most single-touch
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touchpads can also detect three fingers on the touchpad, but no positional
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information is provided for those. In libinput, these touches are termed
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"fake touches". The kernel sends **BTN_TOOL_DOUBLETAP**,
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**BTN_TOOL_TRIPLETAP**, **BTN_TOOL_QUADTAP** and **BTN_TOOL_QUINTTAP**
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events when multiple fingers are detected.
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.. _touchpads_touch_mt:
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..............................................................................
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Pure multi-touch touchpads
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..............................................................................
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Pure multi-touch touchpads are those that can track, i.e. identify the
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location of all fingers on the touchpad. Apple's touchpads support 16
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touches, others support 5 touches like the Synaptics touchpads when using
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SMBus.
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These touchpads usually also provide extra information. Apple touchpads
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provide an ellipse and the orientation of the ellipse for each touch point.
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Other touchpads provide a pressure value for each touch point (see
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:ref:`touchpads_pressure_handling`).
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Note that the kernel sends **BTN_TOOL_DOUBLETAP**,
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**BTN_TOOL_TRIPLETAP**, **BTN_TOOL_QUADTAP** and **BTN_TOOL_QUINTTAP**
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events for all touches for backwards compatibility. libinput ignores these
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events if the touchpad can track touches correctly.
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.. _touchpads_touch_partial_mt:
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..............................................................................
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Partial multi-touch touchpads
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..............................................................................
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The vast majority of touchpads fall into this category, the half-way
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point between single-touch and pure multi-touch. These devices can track N
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fingers, but detect more than N. For example, when using the serial
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protocol, Synaptics touchpads can track two fingers but may detect up to
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five.
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The number of slots may limit which features are available in libinput.
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Any device with two slots can support two-finger scrolling, but
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:ref:`thumb-detection` or :ref:`palm_detection` may be limited if only two
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slots are available.
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.. _touchpads_touch_semi_mt:
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..............................................................................
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Semi-mt touchpads
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..............................................................................
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A sub-class of partial multi-touch touchpads. These touchpads can
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technically detect two fingers but the location of both is limited to the
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bounding box, i.e. the first touch is always the top-left one and the second
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touch is the bottom-right one. Coordinates jump around as fingers move past
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each other.
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Many semi-mt touchpads also have a lower resolution for the second touch, or
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both touches. This may limit some features such as :ref:`gestures` or
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:ref:`scrolling`.
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Semi-mt are labelled by the kernel with the **INPUT_PROP_SEMI_MT** input
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property.
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.. _touchpads_mis:
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------------------------------------------------------------------------------
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Other touchpad properties
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------------------------------------------------------------------------------
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.. _touchpads_external:
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..............................................................................
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External touchpads
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..............................................................................
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External touchpads are USB or Bluetooth touchpads not in a laptop chassis,
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e.g. Apple Magic Trackpad or the Logitech T650. These are usually
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:ref:`touchpads_buttons_clickpads` the biggest difference is that they can be
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removed or added at runtime.
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One interaction method that is only possible on external touchpads is a
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thumb resting on the very edge/immediately next to the touchpad. On the far
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edge, touchpads don't always detect the finger location so clicking with a
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thumb barely touching the edge makes it hard or impossible to figure out
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which software button area the finger is on.
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These touchpads also don't need :ref:`palm_detection` - since they're not
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located underneath the keyboard, accidental palm touches are a non-issue.
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.. _touchpads_pressure_handling:
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..............................................................................
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Touchpads pressure handling
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..............................................................................
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Pressure is usually directly related to contact area. Human fingers flatten
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out as the pressure on the pad increases, resulting in a bigger contact area
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and the firmware then calculates that back into a pressure reading.
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libinput uses pressure to detect accidental palm contact and thumbs, though
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pressure data is often device-specific and unreliable.
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.. _touchpads_circular:
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..............................................................................
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Circular touchpads
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Only listed for completeness, circular touchpads have not been used in
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laptops for a number of years. These touchpad shaped in an ellipse or
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straight.
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.. _touchpads_tablets:
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..............................................................................
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Graphics tablets
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Touch-capable graphics tablets are effectively external touchpads, with two
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differentiators: they are larger than normal touchpads and they have no
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regular touchpad buttons. They either work like a
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:ref:`touchpads_buttons_forcepads` Forcepad, or rely on interaction methods that
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don't require buttons (like :ref:`tapping`). Since the physical device is
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shared with the pen input, some touch arbitration is required to avoid touch
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input interfering when the pen is in use.
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.. _touchpads_edge_zone:
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..............................................................................
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Dedicated edge scroll area
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Before :ref:`twofinger_scrolling` became the default scroll method, some
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touchpads provided a marking on the touch area that designates the
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edge to be used for scrolling. A finger movement in that edge zone should
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trigger vertical motions. Some touchpads had markers for a horizontal
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scroll area too at the bottom of the touchpad.
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