Re: [Visualpython-users] Visual Python in a 3D Immersive Environment

[Shaun P. <sha...@an...>]

On Thu, 2003-06-05 at 11:05, Bruce Sherwood wrote:
> I would be interested in adding your enhancements to Visual, if you are 
> willing. I haven't heard previously of the problems you report. As to 
> the winding rules, where does this come up, other than in the faces 
> primitive? What is the "Stereo Visual Python Program"?
> 
As some of the enhancements are intended to extend the use of Visual
Python in the teaching/modelling environment adding them to the next
release is what I had in mind. It saves the ANU from having a "local"
version instead of a standard version.

On the topic of winding. One of the enhancements I attempted was to
replace the software lighting model with the OpenGL lighting model. The
existing model just uses white light and simulates lighting by
brightening (or dimming) the colour values for each face. Replacing it
with the OpenGL lighting system, while more complex, would allow the
addition of different coloured lights as well as adding different type
of lights (spotlights etc). 
To do this, each shape needs to have associated normals for each
surface. The clasical way to calculate this is to take 3 points on the
surface (usally the vertex points) and use the formula (v1-v2) x (v2-v3)
where <x> is the cross product operator. However the direction of the
normal depends upon whether the points are in clockwise or
anti-clockwise order. Surfaces "face" the viewer in an anti-clockwise
direction (IIRC). It appears with some of the shapes the order is a
mixture of clockwise and anti-clockwise, so some normals face the viewer
and some face away. This results in a blotchy effect on the shapes
surface. While it gives a surreal effect for the viewer, it doesn't
improve the modelling in any way.
This also has consequences for other extensions such as add textures to
shapes and making shapes transparent. 

The Stereo Visual Python program was written by Hugh Fisher to provide
fullscreen and/or quad-buffered stereo displays. He posted the details
on this list in early march. The source is at
http://cs.anu.edu.au/~hugh.fisher/3dstuff/cvisual.zip



> Just yesterday I had an email exchange with people involved with the 
> Geowall consortium (http://www.geowall.org) who use stereo projection in 
> the service of geographic visualization. Their hardware configuration is 
> two projectors with polarizers mounted very close together, projecting 
> onto a screen that preserves polarization. They use passive polarizing 
> glasses. They may try out VPython in their context.

It sound similar to the Wedge except that they have a single screen
rather than the two we use. They may be able to use Hugh's program
without much modification at all.