Real perspective to splot

[<ba...@ar...>]

Dear Developers,

For my phd thesis I needed real 3d perspective for gnuplot. As I didn't
found how to do this in the 4.0.0 version of it, I added it myself.

The small patch able to do this relative to version 4.0.0 is attached. I
extended splot, so it draws perspective by default. If one doesn't like
perspective, he/she must set the perspective eye distance to some huge
value. You can change parameters using "set perspective", view them using
"show perspective". "set perspective" accepts two numbers, the first of
which is the distance between the eye and the hypothetic screen, the
second is the distance between the graph and the screen. I didn't write a
help to it, as my english is poor, however, if you prefer it, I can write
something. And I didn't write code to check the validness of the
parameters. And there's something wrong: if I try to set the parameters,
it works, but complains about a bug, you surely know what that is about,
and how to overrride that.

I think it's a useful extension, so I would ask you to integrate this
feature into the next release of gnuplot.

Thanks:Andras Barta