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From: cflatter@ZIA.AOC.NRAO.EDU (Chris Flatters)
Newsgroups: comp.windows.x
Subject: Re:  Help on X colormap
Message-ID: <9008221650.AA22257@zia.aoc.nrao.edu>
Date: 22 Aug 90 16:50:55 GMT
Sender: daemon@athena.mit.edu (Mr Background)
Organization: The Internet
Lines: 49


Brian Ho writes:

>  I have some problems which are concerning colors display in X-window system.
>  I am trying to display more than 256 different colors, however, everytime
>  when I used up the available color cells (256), I will obtain some (junky)
>  color.  I am wondering if there is a way that I can create another color
>  map to display 256+ colors.  
>
>  I used XAllocColor to allocate the color cells.
>
>  I have tried to use XCopyColormapAndFree() function (Xlib). But it does not
>  seem to work.
>  The following is the configuration on my system under X..
>
>
>  Class : PseudoColor
>  Depth : 8 planes
>  size of colormap : 256 entries
>  red, green, blue mask : 0x0, 0x0, 0x0
>  significant bits in color speci. : 8 bits. (I think it is the problem)

There is no way Brian can get a colour map with more than 256 entries. His
actual problem appears to be that he needs to allocate more than 256 - n
colors where n is the number of colormap entries already allocated by other
clients.

I'm not sure why XCopyColormapAndFree() isn't working.  The O'Reilly
manual (Vol 2) seems to imply that it only works if the original colormap
was created by the client; I need to do some experiments to find out if
that is really the case.

I you want to set up a colormap with a large number of exact colors that is
known in advance you may want to try preallocating a range of colors with
XAllocColorCells() and creating a new colormap with XCreateColormap() if
this fails.

However the private colormap is created you need to exercise some care if
it is associated with a subwindow.  If you are using an ICCCM compliant
window manager you will need to register the subwindow and colormap with
the window manager using XSetWMColormapWindows().  Unfortunately some
ICCCM window managers ignore this and won't install the colormap when
you need it.  If you are using a non-ICCCM window manager you will need
to install the colormap from the client and restore the default when 
necessary (note that ICCCM window managers may regard this as an illegal
act).

				Chris Flatters
				cflatter@nrao.edu