New plotting function surfl

[Kai Habel]

...
>
> Very cool!
>
> It works for me on Mac OSX with Aquaterm as well as with x11. I'm
> unable to try wxt at the moment ... I broke it when I started running
> the developers sources for gnuplot :-(
>
> To be sure, what *I* see is what *you* see, I've attached a pdf.
>
> Ben
>
>
Thanks for trying. Yes, that's how it should look like. If you have not
tried already, an 'interp shading' removes the grid lines and gives even
better graphics.

For the interested, the implementation was not that complicated. The
algorithms are well documented in the OpenGL literature (e.g. "Red Book"
OpenGL [1]).

Kai

[1] http://fly.srk.fer.hr/~unreal/theredbook/chapter06.html