[Fluxus] pixels-renderer weirdness

[gabor papp]

> Check. Then that covers the blur. Actually, what I thought about here was
> that it could be nice to "poke holes" in solid planes using the pixel
> renderer and getting the silhouette of a model as the "hole". I think I can
this can be done with a shader easily for example by inverting the alpha 
values.

(clear)
(define p (build-pixels 256 256 #t))
(with-primitive p (scale 0))

(define hole-vert
     "
     void main(void)
     {
         gl_Position = ftransform();
         gl_TexCoord[0] = gl_MultiTexCoord0;
     }")

(define hole-frag
     "
     uniform sampler2D txt;

     void main(void)
     {
         vec4 c = texture2D(txt, gl_TexCoord[0].xy);
         gl_FragColor = vec4(vec3(c), 1. - c.a);
     }")

(define (animate)
     (with-pixels-renderer p
         (with-state
             (identity)
             (clear-colour #(0 0)) ; transparent clear colour
             (rotate (vector (* 82 (time))
                     (* 11 (time))
                     (* 8 (time))))
             (scale 5)
             (colour #(1 1)) ; opaque cube
             (hint-unlit)
             (draw-cube)))
     (clear-colour #(0 0 1))

     (with-state
         (translate #(-.1 .5 -1))
         (draw-cube))

     ; plane with a cube hole using a shader inverting alpha
     (with-state
         (texture (pixels->texture p))
         (shader-source hole-vert hole-frag)
         (draw-plane)))

(every-frame (animate))


> do that too already, with a transparent clear colour, a plane to cover it,
> then a object before that plane that has it's origin behind it. That would
> make the transparency go "wrong" which would be exactly what I'd like.
i'm not sure how it would work with your method. i would be curious to 
see. other option would be to use stencil buffers, which are especially 
for these kind of things, but we have to implement them in fluxus first :).

best,
gabor