[fluxus] pixel primitive

[Dave Griffiths]

some additions for procedural texturing

(build-pixels width height) makes a new pixel primitive
(upload-pixels) uploads texture data, you need to call this when you've
finished writing to the pixelprim, and while it's grabbed
(pixels->texture pixelprim) returns a texture you can use exactly like a
normal loaded one

pixel primitives render as rectangular planes, textured with the pixel
data, this is useful, but in most cases I think it would be hidden and
applied to another primitive as a texture with (pixels->texture)

you can get/set the pixel data as colour pdata (called "c") and pdata-ops
should work with it ok (but I don't think many of them support colour yet)
and you should be able to create multiple channels etc with
pdata-add/pdata-copy. alpha works too, just use pdata-set with a vector of
size 4.

fixes:
* textures can now be set for a primitive after it's been created, with grab

todo:
* it uses a float texture type for speed, as it doesn't need conversion,
might cause problems on older cards?
* load image to pixel primitive
* save image from pixel primitive

http://www.pawfal.org/dave/images/proctex.png

; animated procedural texture
(clear)
(define a (build-pixels 50 50))

(define (rnd-tex n)
    (pdata-set "c" n (vector (sin (* n 0.1)) (cos (* n 0.01)) (sin (+
(time) n))))
    (if (zero? n)
        0
        (rnd-tex (- n 1))))

(define (render)
    (grab a)
    (rnd-tex (pdata-size))
    (upload-pixels)
    (ungrab))

(translate (vector 2 0 0))
(define b (build-sphere 10 10))
(grab b)
(texture (pixels->texture a)) ; apply the texture to the sphere
(ungrab)

(every-frame (render))