dix: Add hybrid full-size/empty-clip mode to SetRootClip

216bdbc735 removed the SetRootClip call in the XWayland output-hotplug
handler when running rootless (e.g. as a part of Weston/Mutter), since
the root window has no storage, so generating exposures will result in
writes to invalid memory.

Unfortunately, preventing the segfault also breaks sprite confinement.
SetRootClip updates winSize and borderSize for the root window, which
when combined with RRScreenSizeChanged calling ScreenRestructured,
generates a new sprite-confinment area to update it to the whole screen.

Removing this call results in the window geometry being reported
correctly, but winSize/borderSize never changing from their values at
startup, i.e. out of sync with the root window geometry / screen
information in the connection info / XRandR.

This patch introduces a hybrid mode, where we update winSize and
borderSize for the root window, enabling sprite confinement to work
correctly, but keep the clip emptied so exposures are never generated.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Tested-by: Olivier Fourdan <ofourdan@redhat.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/hw/xwayland/xwayland.h b/hw/xwayland/xwayland.h
index a7d71193d..4fcdee5c9 100644
--- a/hw/xwayland/xwayland.h
+++ b/hw/xwayland/xwayland.h
@@ -49,6 +49,7 @@ struct xwl_screen {
     ScreenPtr screen;
     WindowPtr pointer_limbo_window;
     int expecting_event;
+    enum RootClipMode root_clip_mode;
 
     int wm_fd;
     int listen_fds[5];