Aven in stereoscopic 3D

[Olly Betts]

On Sat, Jun 30, 2018 at 12:06:25PM +0000, Pedro Silva Pinto wrote:
> --stereo=buffers is working, but left and right images are way too much
> separated, causing a lot of eye strain: the 3D image pops out of the screen
> so much that you'd have to be cross-eyed to see it comfortably! :) Way too
> close for comfort. Otherwise, the 3D effect is OK.

It seemed OK in the cardboard viewer, but I struggled to make the
coloured glasses work (but they're cereal packet ones so cheap
filters with a lot of colour bleed).

Currently the eye separation is the focal length divided by 20:

    const double APERTURE = 50.0;
    const double FOCAL_LEN = 70.0;
    const double EYE_SEP = FOCAL_LEN / 20.0;

It's possible I cranked that up to make it easier to see it was actually
working correctly and didn't restore the original values.  I'll have to
check where I got that ratio from.

> If the image is moved back closer to screen level, it will be perfect. I
> think the best practices in 3D rendering advise to set the screen plane
> halfway along the Z-axis span: closer parts of the cave render in front of
> the screen plane and more distant parts render 'behind' the screen plane.

OK, I'll have to think about what that means in terms of the values
above.

Meanwhile, if you could try increasing the 20.0 above and suggest a
value which works better than would serve as a useful cross-check.

Cheers,
    Olly