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From: mnp@cs.brown.edu (Matthew Nicholas Pappas)
Newsgroups: comp.windows.x
Subject: Re: Setting up color tables for an image.
Message-ID: <MNP.89Oct19134820@blanche.cs.brown.edu>
Date: 19 Oct 89 17:48:20 GMT
References: : <4743@ncar.ucar.edu>
Sender: news@brunix.UUCP
Organization: Brown University Department of Computer Science
Lines: 72
In-reply-to: davis@karl.ucar.edu's message of 17 Oct 89 20:36:16 GMT

In article <4743@ncar.ucar.edu> davis@karl.ucar.edu (Glenn P. Davis) writes:

   From: davis@karl.ucar.edu (Glenn P. Davis)
   Newsgroups: comp.windows.x
   Keywords: XInstallColormap
   Date: 17 Oct 89 20:36:16 GMT
   Reply-To: davis@karl.UCAR.EDU (Glenn P. Davis)
   Organization: Unidata/UCAR, Boulder CO

   I'm experimenting with a very simple X client to render color images.
   ...
   What is the correct sequence of calls to create and install the new
   colormap? 
   ...
	   cmap = XCreateColormap(dpy, XtWindow(box3), vis, AllocAll) ;
ok
	   XStoreColors(dpy, cmap, colors, ncolors) ;
ok
	   XInstallColormap(dpy,cmap);
NOT ok.  Read the manpage for this function.  Only window managers should
call this function.  Or look at the Gettys & Scheifler book (you know--the
maroon one).

   I have also fooled around with not executing 'XInstallColormap'
   in the main line code, instead adding two event handler to 'box' for
   entering and leaving the box, Install and UnInstall the colormap.
You're still not allowed to call XInstallColormap (even if the mouse entered
your window).

   This latter system works when I'm not running any window manager.
You are in effect acting as the window manager.

   It doesn't with twm, even with ncolors = 64. 
   I assume I'm not being 'a good client'.  
This is true.  But it's hard to know that without trying first.

   What should I be doing?
Assuming your toplevel widget has the same visual type as the root window
(which it must if you are using release 3), call XSetWindowColormap after you
call XStoreColors in the code above.  XSetWindowColormap sets a property on
your toplevel window; this property is read by the window manager, and the
window manager then makes sure that your colormap is installed (using
XInstallColormap) whenever your window has the colormap focus.  Note that the
mous probably has to be inside your window for the window manager to give you
the colormap focus.

If you are using a nonstandard visual, or just want a better sense of the
more complex issues of colormap sharing/installation, read the ICCCM doc,
which is available on expo (18.30.0.212).  It's actually one of the shorter X
documents, and reasonably readable.

   For the case ncolors = 64, I would prefer to set things up so there
   is no 'flash', if possible.
There shouldn't be any serious flash.  Be more specific if you think this is
a problem.

   Thanks

   Glenn P. Davis
   UCAR / Unidata
   PO Box 3000                   1685 38th St.
   Boulder, CO 80307-3000        Boulder, CO  80301

   (303) 497 8643

Good luck,

-matt
Brown Graphics Group
_________________________________________________________________________
   uunet ! brunix ! mnp                           Matthew Nicholas Pappas
or mnp @ {cs.brown.edu, browncs.bitnet }                 Brown University