Initial Xwayland window positioning

      From: Pekka Paalanen <pekka.paalanen@collabora.co.uk>

Many old X11 applications provide -geometry command line option that can be
used to initially position the window. Some obscure applications even rely on
this to work properly. Currently it does not work in Weston, the shell will
unconditionally pick a place of its own.

This series makes -geometry +x+y work.

First it sets up the plumbing needed to deliver initial position from
xwayland.so through libweston-desktop to the desktop shell.

However, shell using the initial position is not enough because Xwayland runs
wild with its wl_surface.commits. Commonly Xwayland does the first commit
before xwayland.so has set up the window geometry, causing the initial
placement to be wrong. It's a race. Xwayland also waits for frame callbacks so
the compositor cannot ignore the commit either, because Xwayland would never
commit again. Writing a completely separate path for Xwayland windows in Weston
core and the shell would be ugly the least and a maintenance nightmare. Hence
the race is suggested to be fixed with more X11 protocol, in the last patch, so
that the first commit from Xwayland happens when everything is actually ready.

A band-aid fix is to handle geometry changes on an already mapped window
attempting to keep the content in place, but because of a related race the
decorations are already drawn, so the window appears to jump rather than just
grow decorations. But, arguably on-the-fly geometry changes should be handled.

The jumping is fixed with the help of a new Xwayland feature:
_WAYLAND_ALLOW_COMMITS property. With that, we not only ensure the geometry is
set before the first commit, but also that the decorations are really fully
drawn.

The last is WIP, because when we investigated the original race, Daniel came up
with a plan described in https://phabricator.freedesktop.org/T7622 . I have not
yet done the XWM reorganization it calls for.

This patch series is also available at:
https://git.collabora.com/cgit/user/pq/weston.git/log/?h=x11-positioning-v1
with a couple more debug patches on top.

The Xwayland patch series needed for _XWAYLAND_ALLOW_COMMITS is:
https://patchwork.freedesktop.org/series/15904/
https://lists.x.org/archives/xorg-devel/2016-November/051913.html

A question was presented, how _XWAYLAND_ALLOW_COMMITS would interact with
_NET_WM_SYNC_REQUEST in both basic and extended forms:
https://lists.x.org/archives/xorg-devel/2016-November/051932.html


Thanks,
pq

Pekka Paalanen (7):
  xwayland: WM debug prints
  xwayland: add set_toplevel_with_position to internal API
  libweston-desktop: add set_xwayland_position API
  xwayland: detect initially positioned X11 windows
  shell: implement set_xwayland_position
  libweston-desktop/xwayland: react to geometry changes
  WIP xwayland: poke _XWAYLAND_ALLOW_COMMITS

 desktop-shell/shell.c                  | 37 ++++++++++++++++
 libweston-desktop/internal.h           |  5 +++
 libweston-desktop/libweston-desktop.c  | 10 +++++
 libweston-desktop/libweston-desktop.h  | 33 +++++++++++++++
 libweston-desktop/xwayland.c           | 18 ++++++++
 xwayland/window-manager.c              | 77 +++++++++++++++++++++++++++++++++-
 xwayland/xwayland-internal-interface.h |  2 +
 xwayland/xwayland.h                    |  1 +
 8 files changed, 181 insertions(+), 2 deletions(-)