Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!crdgw1!galactica!farleyja
From: farleyja@galactica.crd.ge.com (James Farley)
Newsgroups: comp.windows.x
Subject: Transparent windows
Message-ID: <18377@crdgw1.crd.ge.com>
Date: 9 Apr 91 21:08:56 GMT
Sender: news@crdgw1.crd.ge.com
Reply-To: farleyja@galactica.crd.ge.com (James Farley)
Organization: GE Corporate Research and Development
Lines: 21


     Has anyone compiled a listing of the resonses that were posted to this
group concerning how to implement transparent windows?  I remember 
seeing this issue raised more than a few times, with several responses,
but I can't find any of them in the "Frequently asked..." articles.

     What I need to do is have a window that acts like glass, and that can be
drawn on and erased from.  In other words, I need to overlap two windows, one
transparent and one opaque.  The transparent window contain the contents
of the opaque window, and any graphics drawn in the transparent window should
take precendence over the opaque window's contents (i.e. should behave as if 
drawn in the usual manner with a GXcopy GC function).  However, when pixels in
the transparent window are erased (i.e. set to the background value), I want
these pixels to be filled with the contents of the opaque window.  In essence,
I'm trying to implement a background pixel that is a function of another 
window's pixmap.

     Any ideas or past experiences are welcome and appreciated.

                                                     Jim Farley
                                                     farley@crd.ge.com