Unexpected visual effect under GNOME Shell

[Michael Thayer <michael thayer oracle com>]

Hello,

Wondering if anyone can help us with the following question.  In
VirtualBox we need for various reasons to know what the usable area of
each screen is - that translates as the largest rectangle which fits on
that screen without obscuring any panels or similar.  We find that out
by mapping a maximised window on each screen at start-up and checking
its position and dimensions.  To prevent disturbance to the user we
create the window fully translucent, or if the X server does not support
that we use XShape and leave only a single pixel visible.  On GNOME
Shell Wayland edition (what is the right way to say that?) this
unfortunately flashes a black rectangle up on the screen in the area
which should be translucent.  I assume this is Xwayland-related, but is
there any way to prevent it?

For a bit of background, creating a maximised window as we do was the
best way we found of getting the information we need.  Qt does not
provide it directly, _NET_WORKAREA is not quite the right thing either
and not all window managers provide usable strut information as some of
them composite panels directly rather than creating windows for them.
We use the area found for a number of things, in particular: adjusting
the size and position of windows restored from previous sessions if the
old positions no longer fit the current layout (especially to prevent
windows appearing off-screen) and correctly placing the toolbar windows
which we use in seamless mode, which we want to span the bottom
(usually) of a given screen, but above any window manager toolbars or
panels.  Of course, the problem is finding something which works, if not
in all window managers, at least for as many popular ones as possible.

Thanks!
Regards
Michael
-- 
Michael Thayer | VirtualBox engineer
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