Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!hplabs!hp-pcd!hpcvlx!kam
From: kam@hpcvlx.HP.COM (Keith Marchington)
Newsgroups: comp.sys.hp
Subject: Re: X color maps and switching
Message-ID: <101950043@hpcvlx.HP.COM>
Date: 1 Aug 89 17:33:07 GMT
References: <578@mmlai.UUCP>
Organization: Hewlett-Packard Co., Corvallis, OR, USA
Lines: 46



Yes Tony, we have noticed it and in reality, it is intentional.  Here's 
the scenario:

Starbase has a notion of a default setting of the colormap.  I.e. when
a program gopen's a "device" with either RESET or INIT specified in
the mode field, the program can assume that the colormap is set up in
a particular fashion.  Many Starbase programs take advantage of this
fact and do not bother to set up the colormap beyond that.

X, on the other hand, assumes nothing about the initial state of the
colormap.  It allocates BlackPixel and WhitePixel in the default
colormap, but beyond that the rest of the colormap is in an "unknown"
state.  Clients allocate pixels as need in what amounts to a random
order.  

Now, how do we make these two systems work together.  Well, X11 has
the notion of virtual colormaps.  I.e., a client can allocate a whole
colormap and set it up in any fashion it desires.  Then when any
windows that have specified this colormap get the color focus (which
usually follows input focus) the colormap is installed in the
hardware.  For displays that support only one colormap in hardware,
this produces an interesting effect most refer to as "technicolor."  

So, since Starbase applications that are gopen'd with INIT | RESET 
assume that they have a particular colormap and full and unlimited use
of that colormap to change as they see fit, we decided that when an
X window is gopen'd with INIT | RESET, we would create a colormap for
that window and initialize it in the Starbase fashion.  In this way,
old "window dumb" Starbase programs could continue to run and be
visually correct without running rough-shod over the hardware
colormap.  And X applications needn't worry.  The side effect, as you
have seen is that when the Starbase window is visually correct, other
windows are not.

Please note though that this phenomenon is not restricted to Starbase
applications.  Other X applications are beginning to take advantage of
virtual colormaps also and I expect to see this more frequently.  Of
course, in time we should see hardware capable of supporting colormaps
on a per-window basis which will reduce the amount of "technicolor"
that we must put up with.

Ah, the price of flexibility!

Keith