Aven in stereoscopic 3D

[Pedro Silva Pinto]

Hi Olly,

Your changes in the "stereo" branch work for me, except for the placement of
the for loop, because that way both images render on my left eye, and the
right eye is totally black. Remember that the change between left and right
buffers occurs inside StartDrawing, so it needs to be inside the loop.
Attached is the changes.patch (thanks for the 'git diff' tip).

As for the stereo effect: my visual assessment is that the code applies the
same separation to all objects, regardless of their z-axis position. I even
put a ruller against the screen to measure - it's the same separation
always. I think that the subtle 3D effect you mentioned results only from
the 3D objects being rendered in a different plane than the program window
(or the screen frame, if using fullscreen). Then the brain takes over and
completes the illusion.

I'll try different values for the constants involved in the math for
glFrustum to see if I get measurable stereoscopic object separation. Will
post my results.

Cheers,
Pedro