Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!mit-eddie!uw-beaver!Teknowledge.COM!unix!hplabs!hp-sdd!ncr-sd!ncrlnk!wright!odin!ardatta
From: ardatta@odin.wright.edu (Arpita Datta)
Newsgroups: comp.windows.x
Subject: Transparent Pixel values
Keywords: Pixmap, Window, Pixels
Message-ID: <809@thor.wright.EDU>
Date: 2 Nov 89 19:42:44 GMT
Sender: news@wright.EDU
Lines: 14


I have a Pixmap with some graphics objects (lines, arcs, points, etc)
drawn on it. On an Expose event I would like to copy the objects from
the Pixmap onto the exposed areas of the window, rather than redrawing
them on the window.

How can I copy objects drawn on the Pixmap, onto the window without
destroying the tiled background of the window ?  XCopyArea() copies
all pixel values in a particular area and thereby destroys the
background of the corresponding area in the window. The GC boolean
functions (GXCopy, Gxand, GXor, etc) don't seem to be general enough
for arbitrary background tiles. A "transparent" pixmap with objects
drawn in the foreground color would have helped. Is there anyway of
specifying a pixel value to be "transparent" ?