Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!uwm.edu!rpi!iear.arts.rpi.edu!kyriazis
From: kyriazis@iear.arts.rpi.edu (George Kyriazis)
Newsgroups: comp.graphics
Subject: Re: Will PEX become popular? (In English)
Message-ID: <+{=#|6^@rpi.edu>
Date: 8 Mar 90 03:00:53 GMT
References: <490eac1b.20b6d@apollo.HP.COM>
Organization: Rensselaer Polytechnic Institute, Troy NY
Lines: 57

In article <490eac1b.20b6d@apollo.HP.COM> jch@apollo.HP.COM (Jan Hardenbergh) writes:
>
>> 2.	Simulations are becoming more and more popular.  Those need
>> 	physical interactions between geometric objects.  The tree structure
>> 	of PHIGS does not easily allow picturing of those interactions.
>> 	Therefore some more object-oriented approaches to rendering should
>> 	be developed to "replace" PHIGS.
>
>That depends if the objects are rigid bodies. PHIGS is ideal for rigid
>body animation. Just diddle a single matrix and move the object.
>
Hmm..  I can argue about that. PHIGS is good for rigid-body animations that
have an obvious tree structure, eg. robot arms.  I'll bring an easy 
conter example and how it ties into simulation:

Say you have a 3-legged table that can tip over easily over some floor.
You interactively apply forces at different positions of the table to
see how it behaves.  In this example, the tree structure of PHIGS does not
help at all.  Even worse, you have to do your rigid body simulation away
from the graphics interface and then struggle to map your structure into 
some PHIGS tree.  In other words, you are using the massive computational power
you have in your graphics engine just for graphics and doing the simulation
on your poor SPARC/R2000/68040, even if data that you need for simulation
are already calculated by the graphics engine! Ouch!

>What the display list aspect of PHIGS is not good for is deformations of
>a large percentage of the objects. When the number of edits between
>refreshes ( percentChange ) goes up a display list is bad, a display
>list accross the net is worse. But you still use the same basic
>primitives of PHIGS: viewing, modelling matrices, lighting, shading and
>polygons/tristrips or whatevers.
>
I would strongly agree on that.  But, is there another graphics 'standard'
that does this efficiently today?

>I do agree that allowing some sort of object oriented interface to
>PHIGS would be a good idea. PHIGS is, technically, only a year old
>and already has quite a bit of support. It will change, sure. But
>get replaced? I don't think so.
>
My point is that a "graphics standard" will not actually be very useful
in the future.  Something like a "graphics simulation standard" sounds
better.  Graphics engines is a nice idea, but I think it's a waste to keep
them just for graphics work.  Maybe rename them to "accelerator engines" in
the future?  PHIGS will eventually be replaced several years down the road.
Companies will keep on supporting existing standards as long as nothing 
better is in sight, and research environments will keep on trying to 
pursuade companies that what they are working on is better than the existing
standards.. :-)

>
>-Jan Hardenbergh - jch@apollo.hp.com - HP / Graphics Technology Division

----------------------------------------------------------------------
  George Kyriazis                 kyriazis@turing.cs.rpi.edu
				  kyriazis@rdrc.rpi.edu
 				  kyriazis@iear.arts.rpi.edu