Re: Image in a drawing area to .xpm

[Owen Taylor <otaylor redhat com>]

"Michael J. Hammel" <mjhammel@graphics-muse.org> writes:

> Thus spoke Havoc Pennington
> > The X server just throws away the obscured parts - that's why you have to
> > refresh the drawing area when you get expose events. So there's no way to
> > get those pixels since they aren't stored.
> 
> Isn't that whay overlay planes are for?  Xi supports them already, and I've
> been told XFree and Metro are working on it (don't know about the
> workstation vendors, but suspect SGI already supports it).  However, apps
> have to specifically make use of it.  To my knowledge, very few on Linux
> do.  
> 
> Anyone know if Gtk is likely to support overlay planes in the future?

It already does.

If you have overlay planes, then you have (typically) a 24-bit
visual and a 8-bit visual (the overlay planes). GTK+ provides
already provides the ability for an application to query
the available visuals and choose which visual to create
each window in.

However, note that the overlay planes only help you when
a 8-bit window is overlaying a 24-window. This may help
cut down on exposures, but certainly doesn't avoid the
need to handle them.
 
> > If you're keeping a backing pixmap, you could use that though.
> 
> I think you can also turn on backing store for the server, but that may not
> actually solve the original posters problem.

Yes. You can in X (though not through GTK+ directly) 
request backing store for a window, but the X server does not
need to honor the request.

Regards,
                                        Owen