save-under support

Adam Jackson ajax at
Wed Feb 4 14:17:32 PST 2009

On Thu, 2009-01-22 at 17:25 -0500, Patrick O'Donnell wrote:
> I've been told, recently, that "save-under and backing-store under
> 8-bit [visuals] are no longer supported in recent releases".  We
> maintain several old X applications that make significant use of both
> save-under and backing-store (and 8-bit PseudoColor visuals), and this
> news greatly disturbs us.  However, in several days of searching, I
> have been unable to find any definitive pronouncement that that is
> truly the case.

As mentioned downthread, bs and saveunders have never been guarantees,
and did have real bugs that would require the application to correctly
respond to Expose events.

As a trivial workaround, you can enable compositing for your own windows
with XCompositeRedirectSubwindows(dpy, win, CompositeRedirectAutomatic).
If a compositing manager is active, this will have no effect; otherwise,
it will behave essentially the same as bs's WhenMapped state, except,
you know.  Good.

I did attempt to emulate bs by doing this redirection in the server
automagically but never quite got it right.  It's certainly not the goal
to break applications just for fun, I'd love to see this working
properly.  There's also some desire to add something like bs's Always
state to Composite, but so far, nobody's stepped up with code.

- ajax
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