mirror of
https://gitlab.freedesktop.org/libinput/libinput.git
synced 2025-12-20 04:30:06 +01:00
0c51121556
Some ALPS touchpad send the occasional 4095/0 event on slot 1 during two-finger interaction before snapping back to the actual position of the finger. There doesn't seem to be a specific heuristic to predict this so let's hardcode those values. When detected, overwrite the current touch point with the position of the last point. This will likely cause a small pointer jump when the finger later moves to the real position but based on #492 this could be a second later, so all bets are off anyway. Fixes https://gitlab.freedesktop.org/libinput/libinput/-/issues/492 Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
80 lines
4.5 KiB
ReStructuredText
80 lines
4.5 KiB
ReStructuredText
.. _touchpad_jumping_cursor:
|
|
|
|
==============================================================================
|
|
Touchpad jumping cursor bugs
|
|
==============================================================================
|
|
|
|
A common bug encountered on touchpads is a cursor jump when alternating
|
|
between fingers on a multi-touch-capable touchpad. For example, after moving
|
|
the cursor a user may use a second finger in the software button area to
|
|
physically click the touchpad. Upon setting the finger down, the cursor
|
|
exhibits a jump towards the bottom left or right, depending on the finger
|
|
position.
|
|
|
|
When libinput detects a cursor jump it prints a bug warning to the log with
|
|
the text **"Touch jump detected and discarded."** and a link to this page.
|
|
|
|
.. note:: This warning is ratelimited and will stop appearing after a few
|
|
times, even if the touchpad jumps continue.
|
|
|
|
In most cases, this is a bug in the firmware (or kernel driver) and to
|
|
libinput it appears that the touch point moves from its previous position.
|
|
The pointer jump can usually be seen in the :ref:`libinput record
|
|
<libinput-record>` output for the device:
|
|
|
|
::
|
|
|
|
E: 249.206319 0000 0000 0000 # ------------ SYN_REPORT (0) ----------
|
|
E: 249.218008 0003 0035 3764 # EV_ABS / ABS_MT_POSITION_X 3764
|
|
E: 249.218008 0003 0036 2221 # EV_ABS / ABS_MT_POSITION_Y 2221
|
|
E: 249.218008 0003 003a 0065 # EV_ABS / ABS_MT_PRESSURE 65
|
|
E: 249.218008 0003 0000 3764 # EV_ABS / ABS_X 3764
|
|
E: 249.218008 0003 0001 2216 # EV_ABS / ABS_Y 2216
|
|
E: 249.218008 0003 0018 0065 # EV_ABS / ABS_PRESSURE 65
|
|
E: 249.218008 0000 0000 0000 # ------------ SYN_REPORT (0) ----------
|
|
E: 249.230881 0003 0035 3752 # EV_ABS / ABS_MT_POSITION_X 3752
|
|
E: 249.230881 0003 003a 0046 # EV_ABS / ABS_MT_PRESSURE 46
|
|
E: 249.230881 0003 0000 3758 # EV_ABS / ABS_X 3758
|
|
E: 249.230881 0003 0018 0046 # EV_ABS / ABS_PRESSURE 46
|
|
E: 249.230881 0000 0000 0000 # ------------ SYN_REPORT (0) ----------
|
|
E: 249.242648 0003 0035 1640 # EV_ABS / ABS_MT_POSITION_X 1640
|
|
E: 249.242648 0003 0036 4681 # EV_ABS / ABS_MT_POSITION_Y 4681
|
|
E: 249.242648 0003 003a 0025 # EV_ABS / ABS_MT_PRESSURE 25
|
|
E: 249.242648 0003 0000 1640 # EV_ABS / ABS_X 1640
|
|
E: 249.242648 0003 0001 4681 # EV_ABS / ABS_Y 4681
|
|
E: 249.242648 0003 0018 0025 # EV_ABS / ABS_PRESSURE 25
|
|
E: 249.242648 0000 0000 0000 # ------------ SYN_REPORT (0) ----------
|
|
E: 249.254568 0003 0035 1648 # EV_ABS / ABS_MT_POSITION_X 1648
|
|
E: 249.254568 0003 003a 0027 # EV_ABS / ABS_MT_PRESSURE 27
|
|
E: 249.254568 0003 0000 1644 # EV_ABS / ABS_X 1644
|
|
E: 249.254568 0003 0018 0027 # EV_ABS / ABS_PRESSURE 27
|
|
|
|
|
|
In this recording, the pointer jumps from its position 3752/2216 to
|
|
1640/4681 within a single frame. On this particular touchpad, this would
|
|
represent a physical move of almost 50mm. libinput detects some of these
|
|
jumps and discards the movement but otherwise continues as usual.
|
|
If your only encounter with these jumps is the warning printed to the log,
|
|
libinput functions as intended.
|
|
|
|
When you encounter the warning in the log, please generate a recording of
|
|
your touchpad with :ref:`libinput record <libinput-record>` and file a bug.
|
|
See :ref:`reporting_bugs` for more details.
|
|
|
|
Note that it most cases, libinput cannot actually fix the issue. Filing a
|
|
bug is useful to figure out if there are other factors at play or whether
|
|
there are heuristics we can employ to reduce the impact.
|
|
|
|
------------------------------------------------------------------------------
|
|
AlpsPS/2 ALPS DualPoint TouchPad jumping to 4095/0
|
|
------------------------------------------------------------------------------
|
|
|
|
A special case of pointer jumps happens on ``AlpsPS/2 ALPS DualPoint TouchPad``
|
|
devices found in the Lenovo ThinkPad E465 and E550 and likely others with
|
|
the same touchpad hardware. On those devices, the touchpad occasionally
|
|
sends an event for the second finger to move to position 4095/0 before
|
|
moving back to the original position. libinput detects this movement and
|
|
removes it but depending on the interaction this may cause a smaller jump
|
|
later when the coordinates reset to the new position of the finger.
|
|
|
|
Some more information is available in `Gitlab Issue #492 <https://gitlab.freedesktop.org/libinput/libinput/-/issues/492>`__.
|