Path: utzoo!attcan!uunet!husc6!bloom-beacon!EXPO.LCS.MIT.EDU!rws
From: rws@EXPO.LCS.MIT.EDU
Newsgroups: comp.windows.x
Subject: Re: Color allocation
Message-ID: <8907022037.AA05971@expire.lcs.mit.edu>
Date: 2 Jul 89 20:37:14 GMT
References: <3267@portia.Stanford.EDU>
Sender: daemon@bloom-beacon.MIT.EDU
Organization: The Internet
Lines: 14


    The documentation for XAllocColor says,  (O'Reilly vol-2)
    " If a read-only color cell exists that matches the requested RGB value
    that cell is returned. If no matching cell exists and there are no
    unallocated cells the closest available colorcell that has already been
    allocated is returned"

The O'Reilly documentation is incorrect on this point.  For a dynamic
visual (such as PseudoColor), the server transforms your requested RGB values
into the closest values representable by the hardware.  There must be an
exact match of these RGB values with values stored in a colormap entry.

For image processing applications, a Standard Colormap (as described in Xlib)
is often better to use than individual color allocations.