D5452: Handle modifier updates in the same sequence as Wayland does

[Martin Gräßlin]

graesslin created this revision.
Restricted Application added a project: KWin.
Restricted Application added subscribers: kwin, plasma-devel.

REVISION SUMMARY
  Consider the case that capslock gets pressed and released.
  In the case of Weston we have a sequence of:
  
  1. Key press event
  2. Modifier changed event
  3. Key release event
  4. Modifier changed event
  
  KWin however used to send the events in the following sequence:
  
  1. Modifier changed event (on key press)
  2. Key press event
  3. Modifier changed event (on key release)
  4. Key release event
  
  It looks like Xwayland is not able to properly process the sequence
  sent by KWin. And in fact KWin's sequence is wrong as it sends a state
  which does not match. We report that the caps lock is pressed in the
  modifiers prior to the application getting informed about the key press
  of caps lock.
  
  This change aligns KWin's implementation to the behavior of Weston. The
  main difference is that when modifiers change Xkb internally caches the
  serialized modifier states. And KeyboardInputRedirection just forwards
  the modifiers to KWayland::Server::SeatInterface once the processing has
  finished. SeatInterface ignores the forwarding if no states changes, so
  it is fine to do it that way.
  
  BUG: 377155

TEST PLAN
  Not yet tested with an affected Xwayland as I only have 1.18 and the
  problem started with 1.19. But verified the sequence of events with WAYLAND_DEBUG
  and caps lock stil working in QtWayland clients and Xwayland 1.18

REPOSITORY
  R108 KWin

BRANCH
  modifiers-after-key

REVISION DETAIL
  https://phabricator.kde.org/D5452

AFFECTED FILES
  keyboard_input.cpp
  xkb.cpp
  xkb.h

To: graesslin, #kwin, #plasma
Cc: plasma-devel, kwin, spstarr, progwolff, lesliezhai, ali-mohamed, hardening, jensreuterberg, abetts, sebas, apol
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