Path: utzoo!attcan!uunet!husc6!bloom-beacon!EXPO.LCS.MIT.EDU!rws
From: rws@EXPO.LCS.MIT.EDU
Newsgroups: comp.windows.x
Subject: Re: Using Colors in the X environment
Message-ID: <8907022033.AA05964@expire.lcs.mit.edu>
Date: 2 Jul 89 20:33:01 GMT
References: <8906212236.AA27410@sun.com>
Sender: daemon@bloom-beacon.MIT.EDU
Organization: The Internet
Lines: 27


    Application draws three partially overlapping polygons (red, green, blue)
    with an 'OR' operator.  Want the overlapping regions to exhibit the correct
    color (eg: color==white, where the 3 polygons overlap) for this 'OR'
    operation, that is the requirement is for particular pixels to represent
    particular rgb values (upto 64 such "OR-predictable" values may be required
    in this particular case).

Donna Converse has given you one scheme for this, if direct server support of
read-only allocation is required.

XAllocColorCells will do what you want, if you're willing to give up on the
read-only constraint.  You want npixels set to one, and nplanes set to however
many independent OR bits you need.  For your application, you should be able to
specify contig as False.  As nplanes approaches the depth of the window, of
course, the request is likely to fail, and you may have to create your own
colormap.

    In other parts of the application, don't care which pixel represents the
    desired color values (for menus and such), but preferably want to use
    shared pixel allocation to minimize color-cell consumption.

There's no server support for this if you use AllocColorCells, you'd have to
do it yourself by maintaining a mapping on the client side.  What you might
be fishing for is either a mechanism to turn a read-write cell into a read-only
one, or a request like AllocColorCells that takes the RGB values and returns
read-only cells.