diff options
| author | Peter Hutterer <peter.hutterer@who-t.net> | 2014-09-16 15:13:00 +1000 |
|---|---|---|
| committer | Peter Hutterer <peter.hutterer@who-t.net> | 2016-04-28 10:01:20 +1000 |
| commit | 6a22eed4efa2a18664d62c6d8131c05258f869ab (patch) | |
| tree | a4313b12701bd522fa5f6acb10443246f30536ca /doc/touchpad-jumping-cursors.dox | |
| parent | 774be50e68b2d62d9dfbfa3bfffd59be7e89bf3c (diff) | |
touchpad: detect and warn about kernel tracking pointer jumps
If a touch moves by more than 20mm within a single frame, reset the motion
history, effectively discarding the movement. This is a relatively common bug
and almost always needs a kernel fix, so add an explanatory page to the docs.
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Diffstat (limited to 'doc/touchpad-jumping-cursors.dox')
| -rw-r--r-- | doc/touchpad-jumping-cursors.dox | 54 |
1 files changed, 54 insertions, 0 deletions
diff --git a/doc/touchpad-jumping-cursors.dox b/doc/touchpad-jumping-cursors.dox new file mode 100644 index 0000000..e581eb1 --- /dev/null +++ b/doc/touchpad-jumping-cursors.dox @@ -0,0 +1,54 @@ +/** +@page 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 <b>"Touch jump detected and discarded."</b> and a link to this page. + +In most cases, this is a bug in the 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 evemu-record output for the device: + +<pre> + 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 +</pre> + +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. However, +the bug should be fixed at the kernel level. + +When you encounter the warning in the log, please generate an evemu +recording of your touchpad and file a bug. See @ref reporting_bugs for more +details. +*/ |