Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!sdd.hp.com!hp-pcd!hpcvlx!harry
From: harry@hpcvlx.cv.hp.com (Harry Phinney)
Newsgroups: comp.sys.hp
Subject: Re: xwcreate question
Message-ID: <101950200@hpcvlx.cv.hp.com>
Date: 9 Apr 91 19:15:07 GMT
References: <1991Apr04.141312.10371@eye.com>
Organization: Hewlett-Packard Co., Corvallis, OR, USA
Lines: 48

Dan Loewus writes . . .
> When running X11 in combine mode on a hp98731 and executing xwcreate
> with a depth of 24 ( xwcreate graphwin -depth 24 ) two windows are 
> created, the first being a transparent window in the overlay planes
> and the second being the 24 depth window in the image planes ( correct
> me if this is wrong ).  My question is how come the transparent window
> is needed? 

I'm not intimately familiar with xwcreate.  It should not need to create
any extra windows if the server is in combined mode.

John Brown writes:
> The server itself doesn't automatically create two windows.  However,
> if you're running a reparenting window manager (like mwm) then the
> window manager will indeed create additional windows associated with
> the window of interest.  If you're running the server in combined
> mode these windows will reside in the overlay planes.  One of these 
> windows would directly obscure (overlay) the image plane window, and
> so it must be "transparent" in order that you can see the image data
> beneath it.

This is basically correct, although it should be stressed that the
client(s) do not need to do anything special to make this work.  Also,
the window created by the window manager is not really made transparent.
This window is simply logically obscured, and so is not drawn.  When the
server is running in "combined" mode there is no need (nor, I believe,
any means) for any client to create a transparent window.  While a
reparenting window manager will indeed create additional windows, they
will not obscure the image plane window they are associated with.  The
window manager's window(s) will be logically "behind" the image window,
and the X server will insure that the image window is visible.  The
server does this by "painting" the overlay planes "transparent" over the
visible portions of the image window.  The server does this painting
whenever the configuration (size, location, stacking order, etc) of the
windows changes.  The combined-mode servers simply "know" enough to
clear the overlay planes in the visible regions of any image plane
windows.  You can view this as an image plane window "owning" all the
planes, including overlays, within its visible regions.

> It is not
> necessary to create a special transparent window (the window manager
> will do that for you :-)

Again, in combined mode neither the window manager nor the server have
to create a transparent window.  The server only needs to remember to
"clear" the overlays anywhere the image-plane window is visible.

Harry Phinney   harry@hp-pcd.cv.hp.com