Path: utzoo!attcan!uunet!convex!killer!mit-eddie!bloom-beacon!ZERMATT.LCS.MIT.EDU!RWS
From: RWS@ZERMATT.LCS.MIT.EDU (Robert Scheifler)
Newsgroups: comp.windows.x
Subject: Updating a background None window
Message-ID: <19880630215231.6.RWS@KILLINGTON.LCS.MIT.EDU>
Date: 30 Jun 88 21:52:00 GMT
References: <8104@elsie.UUCP>
Sender: daemon@bloom-beacon.MIT.EDU
Organization: The Internet
Lines: 22


    Date: 30 Jun 88 18:40:46 GMT
    From: elsie!ado@cvl.umd.edu  (Arthur David Olson)

    The question on the floor:  is there a better way than Unmapping and reMapping
    to get a transparent window's background corrected after it has been moved?

You are confusing "transparency" with "background None".  Windows with
background None are not the same as X10 "transparent" windows.  An X11
InputOnly window is "transparent" with respect to output (but unlike
X10, you cannot perform graphics through an InputOnly window).  A window
with background None should primarily be viewed as meaning "don't bother
to repaint my contents, I can't define a background that will paint a
reasonable number of correct bits, I'm going to repaint the entire
exposed region anyway".  For example, a window displaying a complex
image might set the background to None.  There is a tradeoff between
setting a background so that you can "see" the window shape in the
period between when an exposure takes place and the application gets
around to repainting (e.g., right after the window is mapped), and
minimizing useless computation by the server.  A window with background
None can be used to approximate an X10 transparent window, but not
completely (e.g., you have to umap it before moving).