[fluxus] upload-pixels fixed + hair example

[dave]

I thought I'd have a play with the pixel-primitive, as I don't think
I've ever used it since I added it. I found a bug in the cvs version
binding which is fixed now. 

It's purpose is to write directly into texture data via the pdata
commands - so you can procedurally generate textures. 

A pic: http://www.pawfal.org/dave/images/knit2.jpg

I've used it to do an example of the shells technique for hair rendering
which makes it's own texture:

http://www.pawfal.org/dave/images/carpet.jpg

(clear)

(define (clear-pixels n)
    (pdata-set "c" n (vector 0 0 0 0))
    (if (zero? n)
        0
        (clear-pixels (- n 1))))

(define (spray n)
    (pdata-set "c" (random (pdata-size)) 
        (vector (flxrnd) (flxrnd) (flxrnd)))
    (if (zero? n)
        0
        (spray (- n 1))))

(define (expand n dst dist)
    (let ((v (vadd (pdata-get "p" n) (vmul (pdata-get "n" n) dist))))
    (grab dst)
    (pdata-set "p" n v)
    (ungrab))
    (if (zero? n)
        0
        (expand (- n 1) dst dist)))

(define (shell n dist incr)
    (expand (pdata-size) (build-cube) dist)
    (if (zero? n)
        0
        (shell (- n 1) (+ dist incr) incr)))

(define p (build-pixels 100 100))
(grab p)
(clear-pixels (pdata-size))
(spray 2000)
(upload-pixels)
(ungrab)

(scale (vector 3 3 3))
(define ob (build-cube))

(push)
(texture (pixels->texture p))
(hint-unlit)
(grab ob)
(shell 30 0 0.003)
(ungrab)
(pop)

(clear-colour (vector 1 1 1))