From: galt@hellgate.utah.edu (Greg Alt)
Subject: Re: VR hardware safety response
Date: Wed, 5 Jun 91 10:06:28 -0600
Organization: University of Utah, CS Dept., Salt Lake City



In article <1991Jun5.031158.15999@milton.u.washington.edu>, kilian@poplar.cray.com (Alan Kilian) writes:

> galt@hellgate.utah.edu (Greg Alt) Says:
>
> > but what about LCD screens?
> > While there is little or no radiation, it is still looking at something
> > only a few inches away from your face.  I would think this is not good
> > and could cause some pretty bad eyestrain.
> 
> Well, not really. The screen is only a few inches from your face but it
> is optically much farther away. Some people say "Optical infinity" but it
> seems more like one meter or so to me.

Well, that makes sense...  So I guess eyestrain would be only as bad as
using a normal monitor (more or less).

> > I wonder what the effect of the optics are on the LCD screen.  I would
> > hope they take the screen farther away from your eyes and enlarge it,
> 
> They do make the screen seem farther away but they don't really "enlarge" it.
> Well they do, but not really. it's like this:
> 
>                             /|
>                            / |
>                           /  |
>                          /   |
>                         /    |
>                        /     |
>                       /|     |
>                      / |     |
>                     /  |     |
>    Your eye-----> .    |     |     You are looking this way --->
>                     \  |     |
>                      \ |     |
>                       \|     |
>                        \     |
>                         \    |
>                        ^ \   |
>                        |  \  |
>                        |   \ |
>                        |    \|
>                        |
>                        |     ^
>                        |     |
> The "real" position ---+     +---  The optical position of the screen.
> ofn the LCD screen
> 
> So the screen "looks" bigger because you think it's farther away, but it does
> not subtend a greater solid angle so it's not really "enlarged"

That's disappointing.  I would think it would be good to make the screen
appear enlarged, but I guess at a few inches from your face, the display would
have a large angle.
 
> > Also, in a couple weeks, I will start to work on a simple 3D graphics
> > system that has perspective views.  I will write it in Turbo C, and 
> > I will post it (or send it to the new cheap-VR ftp site).  I plan on
> > using a hierarchical structure similar to PHIGS, and it will be flexible
> > with color and depth cueing.  If anyone has comments or suggestions,
> > please email me...  I  plan on not supporting lights, but I think I
> > will leave some hooks to allow expansion...
> 
> What are you trying to get? There are many public domain 3D graphics
> systems out there that support all of this. If you are trying to really
> understand 3D than this is the way to go but if you just want to be able
> to draw things get something like the simple phigs package from brown
> university. (Mail to spr@cs.brown.edu because I can't find the IP number)
> they have a PHIGS package that runs with the X-Window system.

I would rather write my own so that it is easy to use with a PC and easy to
modify.  Actually, I cranked out a big part of it last night.  I already
have functions to generate all the matrices, and I plan on re-writing them
to use fixed-point instead of floating-point (I don't have the $400 for a 
387).  I also have the hierachical structure setup to allow executing other
structures...  It will only allow polylines and polymarkers, since the
VR system I will make won't be able to handle polygons (386's are too slow).
But I will leave hooks for this so that it can be added later (I also have
code for fast polygons...)
 
            Greg