[GRASS5] Re: [bug #4155] (grass) d.m will not display remotely

[Glynn Clements]

Kirk R. Wythers wrote:

> > The problem applies to running wish (the Tcl/Tk interpreter), and will
> > affect all Tcl/Tk programs. There isn't anything that d.m or gis.m can
> > do to work around it.
> 
> Can you enlighten me as why with wish shell would work fine locally,  
> but not remotely. I want to think this through because I am guessing  
> that there is some odd OS X thing going on here.

There are two possibilities that I can think of, but both are really
just wild guesses.

1. Your version of Tk relies upon additional pre-defined atoms which
are specific to the MacOSX X server.

2. It is communicating with both local and remote X servers, and using
XIDs obtained from one on the other.

It's conceivable that the latter might come about due to some form of
integration between Aqua and X, e.g. clipboard integration. If Aqua is
trying to pass XIDs from the local X server to wish, and wish is
passing them to the remote X server, that isn't going to work.

Some background:

An atom is a "registered" string which can be referenced by an integer
XID. There are a set of pre-defined atoms (listed in the X11/Xatom.h
header file), but applications can register additional atoms using
XInternAtom[s]. Atoms are shared by all X clients on a given server.

Atoms are used for inter-client communication. Rather than passing
strings such as "CLIPBOARD", clients obtain the XID corresponding to
that string then pass the XID. This reduces traffic and simplifies
comparisons (integer comparison rather than string comparison).

Apart from the pre-defined atoms, the X server allocates atoms in
order, so the XID for a given atom will depend upon when it was
created. Consequently, the XIDs will vary between server instances.

If an application can have connections to multiple X servers (XEmacs
supports this), it has to remember separate XIDs for each X server. 
E.g. the XEmacs instance I'm using to compose this message is running
on a Linux box, with connections to both the local X server and a
remote X server on a Windows box. On the local X server, the XID for
the CLIPBOARD atom is 372, while on the remote X server it is 218.

-- 
Glynn Clements <glynn at gclements.plus.com>