Re: How to check X windows events

Sharon Clay (src++at++rose)
Thu, 11 Jan 1996 11:34:59 -0800

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Actually, complex-glx.c wasn't really a great example of efficiency.

For the basic catching of events I typicall do:
         
    if (XEventsQueued(dsp, QueuedAfterFlush))
    while (XEventsQueued(dsp, QueuedAlready))
    {
        XEvent event;
             
        XNextEvent(dsp, &event);

        switch (event.type)

        {
        }
    }

This gets all the events currently in your local queue and does only one
flush at the begining to get the events X has in its buffer.
You can do this once a frame without being too impacted.
It is good to be able to have your X event handling done in a
separate process (or even separate program) so that your real-time
processes are never explicitly waiting on X.
In your X input handler process you can wrap the above with:
    while (1)
    {
        XEvent event;
        if (XPeekEvent(dsp, &event))
                GetXInput(dsp);
    }
This will put the X input process to sleep if there are no pending events.
You can use a shared memory structure (from the main arena or in a pfDataPool)
to communicate between the event process and your main application.
You want to avoid having your main application collide on locks with your
X input process so grab the events from X into a separate buffer and then
quickly copy them into a buffer for the application to grab when it is ready.
This is what the libpfutil X input handling does.

I try to avoid catching Motion events if at all possibly and if I
do catch them, I throw out all but the last one in a stream as I pull them out
of the X event queue.

src.

-- 
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Sharon Rose Clay (Fischler) - Silicon Graphics, Advanced Systems Dev.
src++at++sgi.com  (415) 933 - 1002  FAX: (415) 965 - 2658  MS 8U-590
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