fdo-mirrors/libevdev
1
0
Fork 0
mirror of https://gitlab.freedesktop.org/libevdev/libevdev.git synced 2025-12-25 05:50:05 +01:00
Code Issues Projects Releases Packages Wiki Activity Actions

Add documentation for axis updates without a tracking ID

Browse source 
If a touch starts and terminates while in SYN_DROPPED, the tracking ID appears
to stay at -1, but the other axes may update. We need to pass these on to the
client since the kernel may buffer the next event with the same value
otherwise. Note this in the documentation so that client's don't create touch
points based on out-of-touchpoint updates.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>
This commit is contained in:
Peter Hutterer 2014-03-19 14:04:59 +10:00
parent 66a78e3391
commit a75e1c3533
1 changed files with 49 additions and 0 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

49
libevdev/libevdev.h
View file

@ -309,6 +309,55 @@ extern "C" {
* in slot 1 maintained the same ABS_MT_TRACKING_ID and only updated the
* coordinates. Slot 1 is the currently active slot.
*
* In the case of a SYN_DROPPED event, a touch point may be invisible to a
* client if it started after SYN_DROPPED and finished before the client
* handles events again. The below example shows an example event sequence
* and what libevdev sees in the case of a SYN_DROPPED event:
* @code
kernel | userspace
|
EV_ABS ABS_MT_SLOT 0 | EV_ABS ABS_MT_SLOT 0
EV_ABS ABS_MT_TRACKING_ID -1 | EV_ABS ABS_MT_TRACKING_ID -1
EV_SYN SYN_REPORT 0 | EV_SYN SYN_REPORT 0
------------------------ | ------------------------
EV_ABS ABS_MT_TRACKING_ID 30 |
EV_ABS ABS_MT_POSITION_X 100 |
EV_ABS ABS_MT_POSITION_Y 80 |
EV_SYN SYN_REPORT 0 | SYN_DROPPED
------------------------ |
EV_ABS ABS_MT_TRACKING_ID -1 |
EV_SYN SYN_REPORT 0 |
------------------------ | ------------------------
EV_ABS ABS_MT_SLOT 1 | EV_ABS ABS_MT_SLOT 1
EV_ABS ABS_MT_POSITION_X 90 | EV_ABS ABS_MT_POSITION_X 90
EV_ABS ABS_MT_POSITION_Y 10 | EV_ABS ABS_MT_POSITION_Y 10
EV_SYN SYN_REPORT 0 | EV_SYN SYN_REPORT 0
* @endcode
* If such an event sequence occurs, libevdev will send all updated axes
* during the sync process. Axis events may thus be generated for devices
* without a currently valid ABS_MT_TRACKING_ID. Specifically for the above
* example, the client would receive the following event sequence:
* @code
EV_ABS ABS_MT_SLOT 0 ← LIBEVDEV_READ_FLAG_NORMAL
EV_ABS ABS_MT_TRACKING_ID -1
EV_SYN SYN_REPORT 0
------------------------
EV_SYN SYN_DROPPED 0 → LIBEVDEV_READ_STATUS_SYNC
------------------------
EV_ABS ABS_MT_POSITION_X 100 ← LIBEVDEV_READ_FLAG_SYNC
EV_ABS ABS_MT_POSITION_Y 80
EV_SYN SYN_REPORT 0
----------------------------- → -EGAIN
EV_ABS ABS_MT_SLOT 1 ← LIBEVDEV_READ_FLAG_NORMAL
EV_ABS ABS_MT_POSITION_X 90
EV_ABS ABS_MT_POSITION_Y 10
EV_SYN SYN_REPORT 0
-------------------
* @endcode
* The axis events do not reflect the position of a current touch point, a
* client must take care not to generate a new touch point based on those
* updates.
*/
/**