[Wayland-bugs] [Bug 89949] Fake finger switching bug in edge scrolling and tapping code

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=89949

            Bug ID: 89949
           Summary: Fake finger switching bug in edge scrolling and
                    tapping code
           Product: Wayland
           Version: unspecified
          Hardware: Other
                OS: All
            Status: ASSIGNED
          Severity: normal
          Priority: medium
         Component: libinput
          Assignee: wayland-bugs at lists.freedesktop.org
          Reporter: peter.hutterer at who-t.net
                CC: jwrdegoede at fedoraproject.org

Created attachment 114942
  --> https://bugs.freedesktop.org/attachment.cgi?id=114942&action=edit
evemu recording

To switch from one to two fingers on a touchpad without slots, the event
sequence is:
BTN_TOOL_FINGER 0
BTN_TOOL_DOUBLETAP 1
SYN_REPORT

On those touchpads, all touches are fake touches (sort-of). The above sequence
will end the currently active touch and then re-start two new touches when the
DOUBLETAP is seen. This triggers a bug message in the edge scrolling code -
since there is no SYN_REPORT between the BTN_TOOL the touch is still in AREA
state when it is re-triggered as a TOUCH_BEGIN.

This also affects the tapping code.

The sequence attached is enough to trigger it, full sequence in the bug here:
https://bugzilla.redhat.com/show_bug.cgi?id=1209151

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