diff options
| author | Peter Hutterer <peter.hutterer@who-t.net> | 2015-12-11 17:40:36 +1000 |
|---|---|---|
| committer | Peter Hutterer <peter.hutterer@who-t.net> | 2016-01-11 15:17:46 +1000 |
| commit | 96fbf848625c0fb2eb53bd7e55664a96155c46ed (patch) | |
| tree | 898829a6f2f9b27edcf0a77be8184568f37f7e86 /doc | |
| parent | 8d79b718fd252c7e813cc8fac0bff7d064c0c524 (diff) | |
tablet: add pressure threshold handling
On tablets with ABS_PRESSURE use a pressure value to determine tip state, not
BTN_TOUCH. This enables us (down the road) to have device-specific pressure
thresholds. For now we use a 5% default for all devices.
The threshold is a range, if we go past the upper range we initiate the tip
down, if we go below the lower range we release the tip again.
This affects two current tests:
* Once we have pressure offsets and pressure thresholds, we're biased towards
pressure. So we can only check that distance is zero when there is a pressure
value, not the other way round.
* When the pressure threshold is exceeded on proximity in with a nonzero
distance, we can only warn and handle the pressure as normal. Since this is a
niche case anyway anything fancier is likely unnecessary.
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Acked-by: Jason Gerecke <jason.gerecke@wacom.com>
Diffstat (limited to 'doc')
| -rw-r--r-- | doc/tablet-support.dox | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/doc/tablet-support.dox b/doc/tablet-support.dox index c95d805..5e6f393 100644 --- a/doc/tablet-support.dox +++ b/doc/tablet-support.dox @@ -35,6 +35,22 @@ Tablet tools may send button events; these are exclusively for extra buttons unrelated to the tip. A button event is independent of the tip and can while the tip is down or up. +Some tablet tools' pressure detection is too sensitive, causing phantom +touches when the user only slightly brushes the surfaces. For example, some +tools are capable of detecting 1 gram of pressure. + +libinput uses a device-specific pressure threshold to determine when the tip +is considered logically down. As a result, libinput may send a nonzero +pressure value while the tip is logically up. Most application can and +should ignore pressure information until they receive the event of type @ref +LIBINPUT_EVENT_TABLET_TOOL_TIP. Applications that require extremely +fine-grained pressure sensitivity should use the pressure data instead of +the tip events. + +Note that the pressure threshold to trigger a logical tip event may be zero +on some devices. On tools without pressure sensitivity, determining when a +tip is down is device-specific. + @section tablet-axes Special axes on tablet tools A tablet tool usually provides additional information beyond x/y positional |