Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!usc!elroy.jpl.nasa.gov!ncar!ico!onecom!onecom.uucp!john
From: john@onecom.uucp (John Brinegar)
Newsgroups: comp.windows.x
Subject: Colormap dilemma
Message-ID: <1991Mar12.235227.28172@onecom>
Date: 12 Mar 91 23:52:27 GMT
Sender: john@onecom (John Brinegar)
Organization: TelWatch Inc., 2905 Wilderness Place, Boulder, CO 80301
Lines: 50


I have been having philosophical discussions concerning colormaps in X, and
I am interested in receiving a dose of conventional wisdom on this topic.

I am currently working on a product that contains two separate X client 
applications with 128 colors each (same 128 colors for both applications).  
These 128 colors have to be settable (read/write) by the application.  These
colors are all specified by their RGB values.  I have tried several means of 
achieving this goal:

1. Allocating 128 read/write (non-shareable) color cells from the default 
   colormap for each application.  This does not work, because there are only
   256 cells in the colormap, and some are already allocated by other
   applications.  This clearly is not a solution because of system resource
   limits.

2. Creating a separate (identical) colormap for each application, and allocating
   128 read/write color cells from the newly created colormap.  This 
   solution has the familiar side effect of colormap swapping when the 
   mouse pointer leaves the application's window.  This is a problem in our
   environment because the colors in our application are critical to the
   functionality of our product.  However, this is only a problem when
   the mouse pointer leaves either of the two applications (because the
   applications have identical colormaps).

   Advantage: Correct colors always available for each application.
   Disadvantage: False colors when pointer outside of both applications.

3. Using XAllocColor() to try to get the exact colors we request in
   each application from the default colormap.  If our applications are the 
   first third party X applications up, the odds are very good that we will 
   successfully allocate all the requested colors (exactly as requested - by 
   RGB values).  However, this is not always guaranteed - other complex, 
   many-colored applications may have all colorcells in the default colormap 
   allocated, and we have to settle for approximations. (See Xlib Reference 
   Manual).

   Advantage: No colormap swapping
   Disadvantage: No guarantees that exact colors will be available

For further information, these applications are running on an IBM RS/6000 
running AIX V3.1 (3003 update).

Are there other alternatives for what I am trying to do, or do I need to choose
between the lesser of two evils (2 and 3)?  Any help with this dilemma is
appreciated.

-- 
John D. Brinegar	{att!uswat, uunet!dunike} !onecom!john
TelWatch Inc.  		(303) 440-4756