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From: sstreep@elvis (Sam Streeper)
Newsgroups: comp.sys.next
Subject: Re: Drawing String in a View (Reply Needed ASAP)
Message-ID: <887@rosie.NeXT.COM>
Date: 4 Jun 91 17:03:51 GMT
References: <1991Jun3.164701.9219@svc.portal.com>
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In article <1991Jun3.164701.9219@svc.portal.com> moose (Michael Rutman) writes:
> ... and why should he do an NXPing()?  The window server will never be  
> more than an eyeblink behind an NXPing().  Or do I misunderstand NXPing().

NXPing() guarantees 2 things for you.  First, you know all your postscript
code has been flushed to the window server.  Second, it does not return
until that code has been rendered.

Other things can do one or both of these functions, so it is not always
necessary.  For example, any time you wait on an event (either by returning
to the event loop or explicitly by using Application's getEvent: method) you
know that your postscript code has been flushed to the window server.
(Remember, though, that the rendering is asynchronous).  Any time you call
a wrapped postscript function that returns a value, the wrap both flushes
and waits for the code to be executed (rendered) before returning.

While I'm on the subject, maybe I'll bring up some NXPing religion.
Your app can spew postscript to the window server much faster than
the window server can render it, so it's possible for your app to
get way ahead of the WS.  When this happens, the relationship between
a user action and the drawing that happens at that time (apparently
in response to the action of the moment) gets mushy.  Mouse dragged
events are coalesced by default, so if you NXPing and the next event
is a drag event, your next drawing will actually reflect the current
position of the mouse.

Pinging can definitely slow you down, because it can force extra communication
between the app and the window server, and this communication is not
always necessary.  It can also speed up rendering, because the app stops
competing with the window server for CPU time until the rendering is
done.  As always, there is no single correct answer, and your mileage may
vary.

-sam

--
Opinions are not those of my employer.  They're not even mine.  They're
probably wrong besides.  How did they get in here, anyway?