Path: utzoo!mnetor!tmsoft!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!usc!snorkelwacker!bloom-beacon!LARRY.MCRCIM.MCGILL.EDU!mouse
From: mouse@LARRY.MCRCIM.MCGILL.EDU
Newsgroups: comp.windows.x
Subject: Re:  How do obtain and/or set a grayscale colormap?
Message-ID: <9009090444.AA06635@Larry.McRCIM.McGill.EDU>
Date: 9 Sep 90 04:44:05 GMT
Sender: daemon@athena.mit.edu (Mr Background)
Organization: The Internet
Lines: 39

> I am writing an X-Windows
[%]
> application to manipulate grayscale medical images.  I would like to
> set the colormap for the window/screen to a grayscale colormap at the
> beginning of the application to save time.  However, I cannot seem to
> set or obtain the grayscale colormap.  Here's what I've tried:

> 1) XCreateColormap() - and then use XAllocColor to set the color
>    cells.  Problem: the colormap returned by XCreateColormap will not
>    let anything be allocated to it.  And yes, I did set AllocAll, not
>    AllocNone.

If you use AllocAll, then you've already allocated all the cells, so of
*course* you can't allocate more.  Just XStoreColor or XStoreColors to
set them to what you want, XSetWindowColormap to tie the colormap to
your windows, and away you go.

> 2) XGetRGBColormaps() - to try to return the standard RGB_GRAY_MAP.
>    Keep getting a segmentation error.

Too many possible causes; I'd have to see the code.  But one quick
question: are you sure such a map has been created on that screen?

What colormap do you want to set?  You have three choices, really.
(Not even that, in some cases.  I am assuming the visual has a mutable
colormap in what follows.)  One is to allocate some subset of the cells
in the default colormap and store your grayscale ramp there; another is
to allocate your own colormap and set it as the colormap for your
window(s), with the third being to use a standard colormap.  Since you
make no mention of doing so, I assume you aren't interested in the
first possibility, and I can't tell what's going wrong with your
attempts at the other two without more information.

					der Mouse

			old: mcgill-vision!mouse
			new: mouse@larry.mcrcim.mcgill.edu

[%] "It's a window system named X, not a system named X Window."