Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!boulder!stan!toml
From: toml@Solbourne.COM (Tom LaStrange)
Newsgroups: comp.windows.x
Subject: Re: Proper way to set the root window's colormap?
Message-ID: <2763@ninja.Solbourne.COM>
Date: 12 Oct 89 22:00:11 GMT
References: <40151@bu-cs.BU.EDU>
Organization: Solbourne Computer Inc., Longmont, Co.
Lines: 51

> I need to know what the "proper" way to set the root window's colormap
> and/or pixmap is.  I am currently just setting the window attributes,
> which works under some window managers but appears to confuse others
> terribly.  What is the "right" way?

Very good question.  From some of the work we have done here, we too have
found that setting the colormap of the root window to be a desirable thing
to do.  If you have a bunch of clients that wish to use a standard colormap
such as RGB_BEST_MAP, it is useful to set that colormap on the root
window so that applications can use it rather than creating there own.
Since most applications create their windows while simply inheriting the
colormap of their parent this should not present too many problems.

There is a problem however in current window managers.  Here is the problem,
at least with twm:  When the window manager starts up, it uses 
DefaultColormap(dpy, screen) as the colormap to install when the pointer
is on the root window.  It also uses this colormap when allocating 
colors for title bars, menus, etc.  Basically the colormap currently
in the root window's attributes is ignored.

What should probably be done is for the window manager to find out what
colormap is currently in the root window's attributes and install it and
use it for its default colormap.  This also requires that the window manager
watch for colormap changes on the root window.

What this buys the user is the ability to set a standard colormap 
(such as RGB_BEST_MAP) on the root window and have all clients, including
the window manager, use it instead of the default colormap.  This eliminates
the "technicolor" flashing as the user moves between applications that
are using this standard common colormap.

This is not a difficult change, we have already changed the yet to be
unveiled swm (Solbourne Window Manager) to do just what I have described
and have noticed no problems whatsoever.  I would also be more than happy
to provide a patch for twm to allow this functionality.

One other interesting problem arises.  Since most Xt clients inherit
the colormap of the root window, setting that colormap to a standard
colormap may cause problems.  A standard colormap may not have any
cells that can be changed.  This causes Xt clients to fail when trying
to allocate a named color.  Solbourne's Xt clients have been fixed
so that they use the closest color available when no color cells
can be allocated.  We expect MIT to provide a similar fix in the
future.

--
Tom LaStrange

Solbourne Computer Inc.    ARPA: toml@Solbourne.COM
1900 Pike Rd.              UUCP: ...!{boulder,nbires,sun}!stan!toml
Longmont, CO  80501