Right now, extension specific actions on window positioning are 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
window positioning 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>
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