#7 Calculating 3 variable surfaces f(x,y,z)

[Jan-Erik Vinje]

I really love the 3d-graph visualization. I'd be even more
excited if I could display the surface of a 3 variable
funtion f(x,y,z) = constant.

In addition it would be nice to be able to display a
gradient vector in the center of each face on the
surface... I'd also love to have several levels of the
same function displayed simultaniously by using
transparency.

f = constant 1 (colour blue, alpha 30%)
f = constant 2 (colour red, alpha 20%)
f = constant 3 (coulour green, alpha 80%)

Or even cooler would be to have a constant scroller.
You define minimum constant and maximum constant and
you drag the scrollbar between those extreems seing
how the surface evolves.