Path: utzoo!attcan!uunet!bloom-beacon!ATHENA.MIT.EDU!swick
From: swick@ATHENA.MIT.EDU (Ralph R. Swick)
Newsgroups: comp.windows.x
Subject: Re: real time x, transparent windows
Message-ID: <8910111540.AA02583@LYRE.MIT.EDU>
Date: 11 Oct 89 15:40:53 GMT
References: <8910110715.AA20180@polyslo.CalPoly.EDU>
Sender: daemon@bloom-beacon.MIT.EDU
Organization: DEC/MIT Project Athena
Lines: 39

> According to the X Toolkit intrinsics, page 66, XtAppAddTimeOut allows
> a timeout procedure to be specified.
...
> can I really get millisecond response time
> granularity?

Probably not.  It's a function of the underlying OS; the value is
passed directly to select().

> Is that a gurantee of the maximum time to the timeout, or the 
> minimum time to the timeout, or in some range?

Minimum, if anything; the timer may expire during dispatching of
some other event (timer, alternate input callback, or XEvent)
which can take arbitrarily long.

> Does this work even if
> you are in a callback procedure, or only if you are in the XtMainLoop
> sitting idle?

The most recent timer event to expire is processed by XtAppProcessEvent
or XtAppNextEvent; there is no preemption.

> What I would like
> to do is have a window underneath another window and have both of them
> visible in the opaque regions and yet be able to change the pattern on either
> one, sort of like having two overhead transparancies stacked one on top of
> the other.

Not supported by the core X11 protocol.

> Failing that, I would like to be able to construct a widget 
> such that a predefined pattern would be displayed permanently in the 
> background, such as a grid or a crosshairs with tick marks on it.

Pretty simple; create a Pixmap (be careful about depth), draw your
static graphics into it, then make it be the window background.  You'll
use up a lot of server resources if you make lots of these, but then
you'd probably expect that to be the case.