Conference bulova::decw_jan-89_to_nov-90

>    The information I have is that Digital systems do not do Backing Store
>    or Save Unders, but I am also told that Decwindows version 2.0 has
>    support for these functions.

Which operating system do you want the answer for?  VMS DECwindows V2
(bundled with VMS V5.3) does not do Backing Store or Save Unders.

Note that it is perfectly okay for applications to specify Backing Store
or Save Unders today.  That way, when the server does implement backing
store and/or save unders, the application will be able to take advantage
of it.  Note that having Backing Store and Save Unders does not make the
application any simpler.  You must still code all the expose logic, as
the protocol does not guarantee that backing store will always be maintained.

Think of Backing Store and Save Unders as performance improvements only.

As of UWS2.2, all Ultrix X servers support backing store and some
support save unders.  I think VAX servers have save unders, while MIPS
servers don't.

Ken

Will backing store really improve performance where you have to 
maintain a pixmap anyway for exposes?

It seems to me like you get an extra "pixmap" creation, copy to on 
occlusion, and copy from on expose where without backing store you just 
have one copy from the pixmap you already have to maintain.

Elapsed time should be shorter with backing store, but you're putting
an extra load on the server that may hurt its performance if it is 
already, for instance, pushing lots of real-time graphics.

Bruce

Backing store is intended for applications that recompute window
contents after expose events.  If you're going to be keeping a shadow
pixmap, backing store is probably not a good idea because the protocol
saved will not pay for the extra memory and computation load.  

Remember, the client must ask for backing store for each window that
wants it.  If you're going to keep a shadow pixmap for a window, don't
ask for backing store.

Ken

See my other reply somewhere close in time to this one as well.  It is sort of
the inverse (or dual or something) of what Ken said.  I suggested that if the
server does do backing store, you might want to at least consider doing only
the slower form of exposes and not keeping a pixmap.  Then if the server dumps
backing store (hopefully not often) do have a recourse, albeit a slow one.

If you see too many exposures coming, then maybe you want to fallback to non-
backedup windows with a pixmap.

Be flexible!  Make decisions dynamically!

Burns

    
    Even though I keep getting cut off at the knee's for complaining about
    these issues... X11 is *really* a distributed architecture:-)  It's
    distributed a thorny problem back to the programmer and will cause
    hundreds of man-years to be spent by endless programmers re-inventing
    all this.  And it's not because X11 couldn't solve the problem --
    even without any real up front cost (i.e. remove one of the mirrors
    from the smoke of it's backing store and *allow* for providing optional
    *guaranteed* backing store - it doesn't need to require it's provision).
    

    I have a customer running a 3rd party software package called
    PRO/ENGINEER (by Parametrics) on a DECstation 5000.  They have been
    told there are problems running the software under DECwindows
    (ULTRIX V4.0 new install), and that a fix is to run the software
    with SAVE UNDER and BACKING STORE turned off.  Could someone tell me
    how to disable these options for the server?  If anyone has any
    ideas, I would be truly grateful.

    						Thanks,
    						Warren
    

This is only a small help...but if noone with more details responds, I think
there is a switch to the server that enables backing store/save unders in
different forms, presumably including disabled.  Perhaps there is a man
page for it to find the right switch?

Or you could switch to VMS :-)  (For just a bit longer, anyway).

Burns

    
    if (DoesBackingStore(screen)) {
        valuemask= CWBackingStore;
         set_win_attr.backing_store = NotUseful;
         XChangeWindowAttributes(display, XtWindow(graph_pw), valuemask,
             &set_win_attr);
    }