@c@b@lStereo
This module supports these viewing modes:
   "monoscopic", the normal non-stereo view,
   "crosseyed", with a pair of left-right eye views arranged horizontally,
                viewed by crossing the eyes to focus on a plane nearer than
                the screen,
   "hardware", which uses the stereo capability available on some Irises,
                viewed with special polarizing glasses, and
   "red/cyan", which draws the left eye's view in red, the right in
		blue-green, viewed using red/blue or red/green glasses.

You can control the sense of depth by adjusting the stereo convergence angle;
large angles give greater sense of depth.  Convergence angle and window
size together determine the viewer-to-screen distance (for a geometrically
correct view) and thus the angular field of view; larger convergence angles
imply wider field of view.

When parameter changes require the angular field of view to vary,
this program attempts to maintain roughly similar views of the object of
interest, using the camera's "focal distance" parameter to indicate
where this is.  (Geomview defaults to 40-degree field of view and 3 unit
focal distance; Stereo generally enforces smaller angular field of view
with correspondingly greater focal length.)

This version of Stereo works only in Euclidean space.

@c@bThe focal plane
You can specify the object of interest by pressing the "Focal Plane" button,
then clicking the right mouse on an object in the geomview window.
The focal plane is redefined to lie at the selected point, i.e. that point
will appear in the same place in both left and right eye views.

You can also use Geomview's "Look At" button, or choose a point of interest
with shift-rightmouse-click in the Geomview window, to select the 
convergence plane.  You may need to press "Look At" more than once.

@c@bField-of-view adjustment
When the field of view changes, the camera is moved along its Z axis
(viewing direction) so that objects in the focal plane maintain constant size
on the screen (though other objects may change dramatically).  (Also,
the camera's clipping planes are adjusted in the same ratio).
The "Fixed Camera" button on the "More..." panel suppresses moving the camera.

A side effect of the focal-plane style is that you must take care when
moving the camera manually: use Focal Plane button (or shift-rightclick)
after flying to tell the stereo module about the new object of interest.

@c@bOther controls
The "Eye Swap" button exchanges the left and right eye's images.  May be
especially handy in hardware stereo mode.

The "More..." panel lets you indicate
  - which geomview camera window to use,
  - the true size of the screen (measured horizontally, in inches),
  - the distance between the viewer's eyes, also in inches, and
  - whether Stereo should attempt to move the camera to preserve the view.
The default camera is "focus", the window most recently pointed at.
The default screen size may be wrong if you've attached a monitor different
from the standard one, or if you're using a projection system.

@c@bIn typical use, to examine an object in stereo, you might:
  - Select some stereo mode.
  - If you have multiple Geomview windows, use the More... panel
	to specify which camera to use.
  - Use "Look At" and/or shift-rightmouse to get some view of an object,
	and make it lie in the stereo convergence plane.
  - Use "Geom Scale" or "Zoom" or "Fly" to adjust the view.
  - Adjust convergence angle to change sense of depth.  (Large convergence
	angles may cause more eyestrain.)
  
As a test of stereo perception, try loading "ico.grp" (a stellated icosahedron)
and "cube".  Select "cube", and scale it to a fairly small size.
Then using "Translate" mode, try to skewer the cube on a spike of ico.grp.

#
 
Effective stereo viewing involves matching configurations in two spaces:
"real" space, where the viewer's eyes and the screen live, and
"virtual" space, where computer-graphical objects live.
This program describes the stereo configuration in terms of several
interrelated parameters: interocular separation "o",
window width "w", stereo convergence angle "c", distance from the
eyes to the "focal" plane "f", and angular field of view "v".

     |-----o-----|
 ---eye (L)     eye (R)
 ||  \           /
 ||   \         /
 |f    \       /
 ||     \     /
 ||      \   /
 ||       \ /
 |-================ "focal plane"
 s        / \
 |       /   \
 |      /     \
 -- RRRRRRRLLLLLLL  screen plane, showing left & right
    |--w--||--w--|  eyes' subwindows as for crosseyed view


The convergence angle (hard to draw in the diagram above) is the
angle between the eye axes looking at something centered in the focal plane.
Eye muscles limit the range of tolerable convergence angles, from approximately
zero up to 10-15 degrees.

The "focal" plane is defined as that plane where stereo disparity is
zero:  objects lying in the focal plane appear at the same place in the left
and right eye subwindows.  The focal plane may or may not coincide (in real
space) with the plane of the screen.  In crosseyed mode, the left and right
eye windows are separated, and the focal plane lies between the viewer and
the screen.  In hardware and red/cyan stereo modes, the eye windows
coincide on the screen, and the focal plane matches the screen plane.

Field of view is related to convergence angle.  The