1.. _touchpad_jumping_cursor: 2 3============================================================================== 4Touchpad jumping cursor bugs 5============================================================================== 6 7A common bug encountered on touchpads is a cursor jump when alternating 8between fingers on a multi-touch-capable touchpad. For example, after moving 9the cursor a user may use a second finger in the software button area to 10physically click the touchpad. Upon setting the finger down, the cursor 11exhibits a jump towards the bottom left or right, depending on the finger 12position. 13 14When libinput detects a cursor jump it prints a bug warning to the log with 15the text **"Touch jump detected and discarded."** and a link to this page. 16 17.. note:: This warning is ratelimited and will stop appearing after a few 18 times, even if the touchpad jumps continue. 19 20In most cases, this is a bug in the firmware (or kernel driver) and to 21libinput it appears that the touch point moves from its previous position. 22The pointer jump can usually be seen in the :ref:`libinput record 23<libinput-record>` output for the device: 24 25:: 26 27 E: 249.206319 0000 0000 0000 # ------------ SYN_REPORT (0) ---------- 28 E: 249.218008 0003 0035 3764 # EV_ABS / ABS_MT_POSITION_X 3764 29 E: 249.218008 0003 0036 2221 # EV_ABS / ABS_MT_POSITION_Y 2221 30 E: 249.218008 0003 003a 0065 # EV_ABS / ABS_MT_PRESSURE 65 31 E: 249.218008 0003 0000 3764 # EV_ABS / ABS_X 3764 32 E: 249.218008 0003 0001 2216 # EV_ABS / ABS_Y 2216 33 E: 249.218008 0003 0018 0065 # EV_ABS / ABS_PRESSURE 65 34 E: 249.218008 0000 0000 0000 # ------------ SYN_REPORT (0) ---------- 35 E: 249.230881 0003 0035 3752 # EV_ABS / ABS_MT_POSITION_X 3752 36 E: 249.230881 0003 003a 0046 # EV_ABS / ABS_MT_PRESSURE 46 37 E: 249.230881 0003 0000 3758 # EV_ABS / ABS_X 3758 38 E: 249.230881 0003 0018 0046 # EV_ABS / ABS_PRESSURE 46 39 E: 249.230881 0000 0000 0000 # ------------ SYN_REPORT (0) ---------- 40 E: 249.242648 0003 0035 1640 # EV_ABS / ABS_MT_POSITION_X 1640 41 E: 249.242648 0003 0036 4681 # EV_ABS / ABS_MT_POSITION_Y 4681 42 E: 249.242648 0003 003a 0025 # EV_ABS / ABS_MT_PRESSURE 25 43 E: 249.242648 0003 0000 1640 # EV_ABS / ABS_X 1640 44 E: 249.242648 0003 0001 4681 # EV_ABS / ABS_Y 4681 45 E: 249.242648 0003 0018 0025 # EV_ABS / ABS_PRESSURE 25 46 E: 249.242648 0000 0000 0000 # ------------ SYN_REPORT (0) ---------- 47 E: 249.254568 0003 0035 1648 # EV_ABS / ABS_MT_POSITION_X 1648 48 E: 249.254568 0003 003a 0027 # EV_ABS / ABS_MT_PRESSURE 27 49 E: 249.254568 0003 0000 1644 # EV_ABS / ABS_X 1644 50 E: 249.254568 0003 0018 0027 # EV_ABS / ABS_PRESSURE 27 51 52 53In this recording, the pointer jumps from its position 3752/2216 to 541640/4681 within a single frame. On this particular touchpad, this would 55represent a physical move of almost 50mm. libinput detects some of these 56jumps and discards the movement but otherwise continues as usual. 57If your only encounter with these jumps is the warning printed to the log, 58libinput functions as intended. 59 60When you encounter the warning in the log, please generate a recording of 61your touchpad with :ref:`libinput record <libinput-record>` and file a bug. 62See :ref:`reporting_bugs` for more details. 63 64Note that it most cases, libinput cannot actually fix the issue. Filing a 65bug is useful to figure out if there are other factors at play or whether 66there are heuristics we can employ to reduce the impact. 67 68------------------------------------------------------------------------------ 69AlpsPS/2 ALPS DualPoint TouchPad jumping to 4095/0 70------------------------------------------------------------------------------ 71 72A special case of pointer jumps happens on ``AlpsPS/2 ALPS DualPoint TouchPad`` 73devices found in the Lenovo ThinkPad E465 and E550 and likely others with 74the same touchpad hardware. On those devices, the touchpad occasionally 75sends an event for the second finger to move to position 4095/0 before 76moving back to the original position. libinput detects this movement and 77removes it but depending on the interaction this may cause a smaller jump 78later when the coordinates reset to the new position of the finger. 79 80Some more information is available in `Gitlab Issue #492 <https://gitlab.freedesktop.org/libinput/libinput/-/issues/492>`__. 81