[Fluxus] Pdata-index-map!

[gabor papp]

hi Luis,

> Thanks Gabor for the script about finding the verts number,
> it'great.
you are welcome. i'm glad it's useful.

> I have another question, when you say that the "pdata-index-map!
> supplies the current pdata index number to the procedure", do you
> refer that I am giving a name to the current pdata?
no, it has a different function. i believe you are familiar with 
pdata-ref and pdata-set! to read and write pdata. if you understand 
pdata-map!, pdata-index-map! is similar it just gives you the index of 
the pdata in the list as well as its current value.

the following example sets the colour of the torus vertices. low indices 
get dark colour, high ones get lighter ones, which demonstrates the use 
of the index in pdata-index-map!

(clear)

(define prim (build-torus 1 2 10 20))

(with-primitive prim
     (hint-vertcols)
     (pdata-index-map!
         (lambda (i c)
             (/ i (pdata-size)))
         "c"))

best,
gabor