XDRIVER failing to repainting on some X11 Servers?

[Lawrence Houston]

GrassHoppers:

On Tue, 5 Oct 1993, Darrell McCauley wrote:

> Lawrence Houston (houston at norton.geog.mcgill.ca) writes on 2 Oct 93:
> >We recently observed a problem with GRASS 4.1's XDRIVER (Spring 1993 -
> >Patch Level #1) as it runs on some of our X11 Servers and but not others. 
> >Hoping that some "nice" GRASS User(s) might be able to provide an
> >explaination for a problem with failing to repaint displayed images after
> >being covered partially or fully by another windows.  With the binaries
> 
> as you have deduced, this seems to be a problem with the server
> (and not grass). I've personally never noticed this behavior
> using Sun or MIT servers.
> 
> --Darrell

Well the cause of the failure to "Repaint" following an Expose Event turns
out to be caused by some code in XDRIVER (Serve_Xevent.c) which had been
commented out in the Update #1 Package.  This was code XDRIVER uses to
support X11 Servers which do NOT support the Backing Stores, but instead
does its own repainting from a Backup Pixmap.  It was Olga Waupotitsch at
CERL who had commented out the code as an experiment to reduce multiple
repainting when serveral Events are received.  Taking the Comments out
re-enables repainting for these "dumb" Servers, although a bit slow when
the delays over the net are long! 

In addition Martijn van Leusen suggests some X11 Servers can be forced to
support Backing Stores with the "-gs" parameter.  I have yet to try that,
but that might be another solution! 

Lawrence Houston,
McGill University.