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There are a number of use-cases where tapping may be desirable, but tap-and-drag is not, e.g. where tapping is used to select multiple items in a list. Having tap-and-drag on hinders this, and the nature of the interaction means it cannot be detected based on timeouts, movement thresholds, etc. Provide an option instead to turn tap-an-drag off. Tap-and-drag remains enabled by default (though tapping is disabled by default). For the touchpad tap state diagram, the new option disables the transition from state TOUCH to state TAPPED and releases the button immediately instead. This means that multitap-and-drag is disabled too since we now just loop around in the single-tap state for multitap. It also makes tapping more responsive - we don't have to wait for the timeout before we know whether it's a tap event. The first touch time is noted, we now send the button press with the time of the first touch and the release with the time of the release. This ensures a realistic time diff between the two events. https://bugs.freedesktop.org/show_bug.cgi?id=93502 Signed-off-by: Peter Hutterer <peter.hutterer@who-t.netto> Reviewed-by: Hans de Goede <hdegoede@redhat.com>
70 lines
3.5 KiB
Text
70 lines
3.5 KiB
Text
/**
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@page tapping Tap-to-click behaviour
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"Tapping" or "tap-to-click" is the name given to the behavior where a short
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finger touch down/up sequence maps into a button click. This is most
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commonly used on touchpads, but may be available on other devices.
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libinput implements tapping for one, two, and three fingers, where supported
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by the hardware, and maps those taps into a left, right, and middle button
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click, respectively. Not all devices support three fingers, libinput will
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support tapping up to whatever is supported by the hardware. libinput does
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not support four-finger taps or any tapping with more than four fingers,
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even though some hardware can distinguish between that many fingers.
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Tapping is **disabled** by default, see [this
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commit](http://cgit.freedesktop.org/wayland/libinput/commit/?id=2219c12c3aa45b80f235e761e87c17fb9ec70eae)
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because:
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- if you don't know that tapping is a thing (or enabled by default), you get
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spurious button events that make the desktop feel buggy.
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- if you do know what tapping is and you want it, you usually know where to
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enable it, or at least you can search for it.
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Tapping can be enabled on a per-device basis. See
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libinput_device_config_tap_set_enabled() for details.
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@section tapndrag Tap-and-drag
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libinput also supports "tap-and-drag" where a tap immediately followed by a
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finger down and that finger being held down emulates a button press. Moving
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the finger around can thus drag the selected item on the screen.
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Tap-and-drag is optional and can be enabled or disabled with
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libinput_device_config_tap_set_drag_enabled(). Most devices have
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tap-and-drag enabled by default.
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Also optional is a feature called "drag lock". With drag lock disabled, lifting
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the finger will stop any drag process. When enabled, libinput will ignore a
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finger up event during a drag process, provided the finger is set down again
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within a implementation-specific timeout. Drag lock can be enabled and
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disabled with libinput_device_config_tap_set_drag_lock_enabled().
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Note that drag lock only applies if tap-and-drag is be enabled.
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@image html tap-n-drag.svg "Tap-and-drag process"
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The above diagram explains the process, a tap (a) followed by a finger held
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down (b) starts the drag process and logically holds the left mouse button
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down. A movement of the finger (c) will drag the selected item until the
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finger is released (e). If needed and drag lock is enabled, the finger's
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position can be reset by lifting and quickly setting it down again on the
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touchpad (d). This will be interpreted as continuing move and is especially
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useful on small touchpads or with slow pointer acceleration.
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If drag lock is enabled, the release of the mouse buttons after the finger
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release (e) is triggered by a timeout. To release the button immediately,
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simply tap again (f).
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If two fingers are supported by the hardware, a second finger can be used to
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drag while the first is held in-place.
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@section tap_constraints Constraints while tapping
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A couple of constraints apply to the contact to be converted into a press, the most common ones are:
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- the touch down and touch up must happen within an implementation-defined timeout
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- if a finger moves more than an implementation-defined distance while in contact, it's not a tap
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- tapping within @ref clickpad_softbuttons "clickpad software buttons" may not trigger an event
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- a tap not meeting required pressure thresholds can be ignored as accidental touch
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- a tap exceeding certain pressure thresholds can be ignored (see @ref
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palm_detection)
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- a tap on the edges of the touchpad can usually be ignored (see @ref
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palm_detection)
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*/
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