Hi there fluxers,
Something odd is happening when I try and create custom pdata,
following the example in the particles.scm file. I use pdata-set to
create a pdata field called "age" which will be the particle age, and
a field called "p-end" which will be the final position of the
particle, but I am unable to alter the "age" or "p-end" fields (they
are always 0) whereas I can alter the "p0" and the rest of the fields
just fine. Try the code below - it will complain that "p-end" is not
a vector in the (vdiv ...) function n (update)
(Note: this code is just to try things out - there are definitely
better ways of doing this! I would NOT use this for any real purpose
other than teaching / learning)
;--- begin moving-particles.scm -------------
(clear)
(define particle-count 100)
(define stuff
(with-state
(hint-anti-alias)
(build-particles particle-count)))
; init one particle
(define (init-particles n)
(pdata-set "p" n (vector -10 0 0))
(pdata-set "p-end" n (vector (+ (* 10 (flxrnd)) 10) 0 (* 3
(flxrnd))))
(pdata-set "age" n 0)
(pdata-set "c" n (vector 1 1 1))
(pdata-set "s" n (vector 1 1 1))
(cond [(> n 0)
(init-particles (- n 1))]
[else 0])
)
(with-primitive stuff
(init-particles (pdata-size))
(pdata-copy "p" "p0")
)
(define (update p)
(with-primitive p
(pdata-map!
(lambda (age)
(modulo (+ age 1) 1000)) "age")
(pdata-map!
(lambda (p p0 p-end age)
(vdiv (vsub p-end p0) age))
"p" "p0" "p-end" "age")
)
)
(every-frame
(update stuff))
