Path: utzoo!attcan!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!uunet!samsung!usc!elroy.jpl.nasa.gov!lll-winken!cs!spl
From: spl@cs.nps.navy.mil (steve lamont)
Newsgroups: comp.graphics
Subject: Re: IRIS ANIMATION QUESTIONS
Message-ID: <1165@cs.nps.navy.mil>
Date: 4 Aug 90 19:54:35 GMT
References: <90Aug4.130538edt.7478@neat.cs.toronto.edu>
Reply-To: spl@cs.nps.navy.mil (steve lamont)
Organization: Naval Postgraduate School, Monterey CA
Lines: 43

In article <90Aug4.130538edt.7478@neat.cs.toronto.edu> mgreen@cs.toronto.edu (Marc Green) writes:
>I've received a number of responses to my question on IRIS animation.
>Every one suggested the same solution: hide images in the back and z
>buffers and lrectwrite to the front buffer. This is far too slow. 

Lrectwrite() does not move pixels from the back buffer to the front buffer.  
This is the job of swapbuffers().  I haven't used a PI for this kind of stuff
so I don't know how fast or slow lrectwrite() is in writing from *memory* to
the buffer, but it should be reasonably quick -- backplane speeds, I'd venture
to guess.

>It appears that the Personal IRIS is simply not very good for
>animation. You can only copy a 200x200 area in one sweep. ...

I don't know where the 200x200 restriction comes in.  I've copied larger
images than that without problem.  Is the PI's GL different in this respect
from the 4D/2x0 series?  I don't recall seeing any difference mentioned in the
documentation.  
 
When I go in to abuse the IRIS this afternoon, I'll take a look.

>       ... You can only copy a 200x200 area in one sweep. The only
>reasonable way to do animation of large, complex scenes is to hardware
>pan and scroll to by changing the entry point in memory. The IRIS,
>strangely, does not have this feature, although it is common in lower
>powered systems, such as those based on the TI34020 chip and other AT
>boards.

The IRIS's long suit, I'll admit, is really not in pixel pushing, as much as
in dealling with geometric objects, more or less directly.  You don't say what
kind of animation you're doing or how you're rendering the scenes, so it is
impossible to suggest, with any possibility of being helpful, any ways
improving graphic performance.  Just remember that the SGI has a "geometry
engine" architecture.  You may have to rethink your application completely
in order to get best use of the machine.

							spl (the p stands for
							polygon pusher)
-- 
Steve Lamont, SciViGuy -- (408) 646-2752
NPS Confuser Center, Code 0141/Naval Postgraduate School Monterey, CA 93940
"You're okay," said Honeysuckle.  "The dogs like you."
			- Charles Bukowski, "How to Get Published"