[Gzz] Buoy geometry, third version

[Tuomas Lukka]

Ok, gfx/demo/vpbuoy now contains Cg code for a buoy geometry which, to me, seems
to be getting closer to the right one.

The basic idea of using pencils of lines (pencil = set of lines crossing in a 
point),
but instead of two we use three, the third one crossing at the horizontal ideal 
point
(i.e. horizontal, non-crossing lines for those people still thinking in 
Euclidean
terms ;) ;)

When outside the circle, the horizontal lines are used, offsetting the points 
slightly to 
left or right, and when inside, the buoys are projected.

The radius of the circle onto which they are projected is somewhat smaller for 
the points closer 
to the center.

Of course, there's still some adjustment to do; there are some discontinuities. 
But nothing
that can't be handled. Check it out and give your opinions.

        Tuomas