Quoting Troels Henriksen <athas@sigkill.dk>:

wagnerdm@seas.upenn.edu writes:

That strategy doesn't work when the layout of all the windows changes,
since a window cannot be mapped at two places (and, potentially,
sizes!) at once.

You could dump the contents of the workspace region to a pixmap, render
that pixmap to a new (unmanaged) window covering the entire workspace,
perform window movement/mapping behind it and unmap the covering window
at the end.  This would work, but it's ugly and complex.  I doubt a
simple and robust solution to this aesthetic issue can be conceived.

Cute. The generalization of this idea leads directly to a simple, robust solution: never unmap clients, and using OpenGL compositing to hide them instead. ;-)