Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!pasteur!ucbvax!agate!web8h.berkeley.edu!adamj
From: adamj@web8h.berkeley.edu (Adam J. Richter)
Newsgroups: comp.windows.x
Subject: Re: Graphics Context in X11
Message-ID: <6799@agate.BERKELEY.EDU>
Date: 31 Jan 88 06:29:15 GMT
References: <5163X@utah-cs.UUCP>
Sender: usenet@agate.BERKELEY.EDU
Reply-To: adamj@widow.berkeley.edu (Adam J. Richter)
Organization: University of California, Berkeley
Lines: 32
Keywords: caching, cost

In article <5163X@utah-cs.UUCP> shebs@utah-cs.UUCP (Stanley Shebs) writes:
>The X11 Xlib document warns against using too many graphics contexts and
>switching between them, as opposed to re-setting the attributes of a few.

	Good advice if you're using the server that I've been porting
for Jupiter Systems ("graphics far beyond your puny earthling
needs.").  Their system has eight cached GCs.  (Some of them are used
by server GCs to do things like drawing the cursor; in practice,
you'll have fewer.)

	While I think that GCs are a good idea, I don't think that
there is a good general rule for GC usage.  If there are free hardware
GCs, then, obviously, you want use them.  If there are more software
GCs than hardware GCs and a lot of software GCs are being accessed,
then you'll "thrash."  It's just like physical and virtual memory.

	As for the Jupiter, it can change parts of a GC
element-by-element, so changing the GC is cheap.  On the other hand,
if you were using a system in which you could only load hardware GCs
whole-hog, then it would always be better to use separate GCs.

	This sort of hardware information might be useful to ask for
in the form of an extension.  On the other hand, I'm hoping for a
public-domain NeWS.

P.S.--> Has anybody out there noticed that all the X protocol requests,
	except the ellipse stuff, can be generalized to N dimensions?

Adam J. Richter			adamj@widow.berkeley.edu
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