[Visualpython-users] active and passive stereo

[Bruce S. <bas...@un...>]

John Zelle has contributed to Visual code that handles both "active" and 
"passive" stereo, and this is now available in the Windows version of 
VPython (Linux/Unix to follow quickly). Many thanks to John. Also thanks 
to Hugh Fisher who contributed to an earlier version of "active" stereo 
and to the design.

This new capability is quite fantastic. Old demos leap out of the screen 
at you, with the addition of a single line of code!

 From the new documentation for displays:

scene.stereo
Stereoscopic option; scene.stereo = 'active' will render alternating 
left eye/right eye images for viewing through shutter glasses if the 
graphics system supports quad buffered stereo.

Setting scene.stereo = 'passive' will render a scene with double window 
width, for display using two polarized projectors (with viewing using 
simple passive polarized glasses for stereo).

If stereo equipment is not available, setting the option has no effect, 
and scene.stereo will have the value 'nostereo'.

(Quad buffered 'active' stereo is only available on specialised graphics 
systems that have the necessary hardware and shutter glass connector, 
such as SGI machines and PCs with nVidia Quadro or 3DLabs Wildcat 
graphics cards. It generates the illusion of depth by rendering each 
frame twice from slightly different viewpoints corresponding to the left 
and right eyes. Special shutter glasses are synchronised with the 
alternating images so that each eye sees only the matching frame, and 
our brains do the rest. It's called 'quad buffered' because there is an 
OpenGL buffer per eye, both double-buffered for smooth updating. 
'Passive' stereo requires a video card that can drive two monitors, or 
two projectors.)

scene.stereodepth
By default, the front of the scene is located at the location of the 
physical screen, which reduces eye strain. Setting scene.stereodepth = 1 
moves the center of the scene to the location of the physical screen, 
with the front half of the scene seeming to stick dramatically out of 
the screen. scene.stereodepth = 2 moves the scene fully in front of the 
physical screen, for maximally dramatic stereo effect.

Note: There is work in progress to implement "anaglyph" stereo (red/blue 
glasses) , but this isn't quite ready.

Small detail: stonehenge.py has been slightly altered to remove the 
crosshairs, which got in the way if you add stereo. None of the standard 
demos have stereo turned on, but this is trivially easy to do.

Bruce Sherwood