Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!purdue!bu-cs!madd
From: madd@bu-cs.BU.EDU (Jim Frost)
Newsgroups: comp.windows.x
Subject: Re: X double buffering
Message-ID: <40616@bu-cs.BU.EDU>
Date: 17 Oct 89 16:02:41 GMT
References: <181@wbcs.UUCP> <170@med.Stanford.EDU>
Reply-To: madd@cs.bu.edu (Jim Frost)
Followup-To: comp.windows.x
Distribution: usa
Organization: Software Tool & Die
Lines: 29

In article <170@med.Stanford.EDU> rick@hanauma.UUCP (Richard Ottolini) writes:
|In article <181@wbcs.UUCP> doug@wbcs.UUCP (Doug Kratky) writes:
|>Could someone give me hints, code fragments, or examples
|>on "double-buffering" with X?
|
|Draw into an offscreen pixmap, then copy it onto screen.
|This works well on a fast X-server such as a DEC 3100 and not so well
|on a slow server such as any Sun.

Actually it works pretty well even on the 386i server (the SLOOOW
server), especially if compiled with gcc.  When working for my
previous employer we used this method to make graphics changes seem
atomic to the user; the copies were fast enough to be generally
unnoticable, especially if the copy is limited to the changed area.
We were using a fullscreen window for our display and it still worked
well.  On fast servers it works extremely well, although you're not
going to get real-time animation out of it as you can with true
double-buffering (our application worked much better under SGI GL with
or without double buffering than under X, imagine that :-).

|(Not all drawing operations that work on screens work on pixmaps such
|as erase.)

True, but it's simple enough to fill a rectangle to take care of this
case.

jim frost
software tool & die
madd@std.com