[Kst] Ways to evaluate expressions...

[Brisset, Nicolas]

>   You can't with a data plugin yet.  We're going to make a 
> new plugin model in the next release which will let you do 
> that.  
I hope it will also include the possibility to provide custom
configuration widgets, as that would open the door to much more usable
plugins in some cases. It could be an option: either use the existing
string/scalar/vector input type, or provide a custom class with a
special tag in the .xml + corresponding implementation.

> At best you can just copy the existing evaluator into 
> your tree.  
I hoped to import it into the svn tree if that's OK. The license allows
it and it is quite small so that it sounds like a good option. I will
have to look at where to import it and how to add it to the build
system. It lives in its own namespace, so that it can probably be added
anywhere safely. I suppose the cleanest way is to put it in a separate
library... 

> I have some ideas I want to experiment with in 
> the evaluator to make it much faster yet, but that probably 
> won't happen until the summer at the earliest.
The "muparser" looks quite good (also performance-wise) from what I can
tell. If you don't know it already, I think it is definitely worth
looking at. 

On a related note, I have looked again at qwtplot3d recently
(http://qwtplot3d.sourceforge.net/), and it looks very good: efficient,
nice examples, clean API... Ted will probably be interested to know that
it already supports vector fields :-) And once we have a clean design to
plug such external renderers into kst, we could get nice 3D plots (also
in qwtplot3d) "for free" (I'd say O(days) and not O(months)).

Nicolas