Right now, extension specific actions on screen closing implemented by wrapping
the ScreenRec's PositionWindow() proc pointer: the extensions are storing the
original pointer in their private data and putting in their own one. On each
call, their proc restores the original one, calls it, and switches back again.
When multiple extensions doing so, they're forming a kind of daisy chain.
(the same is done for lots of other procs)
While that approach is looking nice and elegant on the drawing board, it's
complicated, dangerous like a chainsaw and makes debugging hard, leading to
pretty blurred API borders.
This commit introduces a simple approach for letting extension hook into the
screen closing path safely, w/o having to care much about side effects with
the call chain. Extensions now can simply register their hook proc (and an
opaque pointer) and get called back - w/o ever having to mess with the
ScreenRec's internal structures. These hooks are called before the original
vector (usually handled by DDX/screen driver directly) is called.
Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
e6b506d46f