[Wayland-bugs] [Bug 67563] Touch events dropped after multiple touchpoints hit at once

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=67563

--- Comment #8 from Neil Roberts <neil at linux.intel.com> ---
Experimenting with the touch events a bit more, I think I've found three
separate problems:

1- I was a bit too hasty with my patch and it doesn't work quite right. When it
gets the sync event it immediately changes the slot number and then sets the
pending event. Then when it comes to flush the events it will use the new slot
number to flush the old pending event so the events can have the wrong finger.

2- If you get more than 32 events in one read then it resets the pending events
before processing the next batch in evdev_process_events. If I press all four
fingers down at once then it ends up with more than 32 events and the sync
message is in the second batch. The pending flag for the last finger gets
cleared so it is never emitted. I think this is what I was seeing when bashing
the screen with four fingers as described in comment #6.

3- If you release a finger and press it down again quickly you can get get the
up and down events in the same batch. However the pending events are always
processed in the order down then up so it will end up notifying two down events
and then an up. This could be what Artie is seeing with a single finger,
although I think that would only make sense if Artie's device is reporting the
multi-touch events and not the ABS_X/Y events.

I think it would be a good idea to rethink the batching mechanism a bit so that
it really only batches the motion events and anything else should cause a
flush. Perhaps the the pending motion events should be queued per-slot as well
rather than trying to have a single flag. I will experiment with a patch.

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