vizcave and quad-buffered stereo

[AySz88]

Confirmed - thanks!

Links are much more powerful than I anticipated - one can add/subtract/etc. sensors by using pre/postMultiplyLinkable and the appropriate transformations along with them.

FYI, I had a tough time realizing "pre" multiplication is "before", which would be "to the right" instead of "to the left" in OpenGL's conventional notation. It was obfuscated by the link operators documentation, which seems to use left-to-right row-major matrix multiplication, a DirectX math notation, instead of right-to-left column-major, which is OpenGL's convention. Vizard's other documentation pages use OpenGL convention.