Andrew Sorensen posted some code in the Impromptu mailing list showing how to add graphics (and various other things) on top of a code ‘image’. As usual I regret not having a whole free day to play with this, but just by messing around a bit with some parameters it’s easy to achieve some interesting effects…

Here’s the source code from Andrew:

(gfx:start-live-video)

(define canvas (gfx:make-canvas 640 480))

(define gl (gl:make-opengl))
(gl:open-opengl gl '(0 0 640 480))

;; draw code behind a rotating cube
;; if you wanted you could now call gfx:start-movie-capture
;; and pass the gl context where canvas usually goes.

(define loop-gl
    (lambda (beat)
       (let* ((code (gfx:get-code-image))
              (flipped (gfx:flip-image code))
              (width (car (gfx:get-image-size code)))
              (height (cdr (gfx:get-image-size code))))
          (gl:clear gl (+ *gl:color-buffer-bit* *gl:depth-buffer-bit*))
          (gl:window-pos gl 0 0 .99)
          (gl:draw-pixels gl width height *gl:rgba* *gl:unsigned-byte* flipped)
          (gl:load-identity gl)
          (gl:translate gl 0 0 .5)
          (gl:rotate gl (* beat 10) 1 1 1)
          (gl:color gl 1 1 1 1)
          (glut:wire-cube gl 0.5)
          (gl:flush gl)
          (gl:update-backing-image gl)
          (objc:release (+ (now) 5000) code flipped)
          (callback (*metro* (+ beat (* .5 1/6))) 'loop-gl (+ beat 1/6)))))

(loop-gl (*metro* 'get-beat 4))8

;; define an image to use as layer3

(define layer3 (gfx:make-image 640 480))

;; draw paths to layer3
(define draw-on-layer3
    (lambda (beat)
       (gfx:clear-image layer3)
       (dotimes (i 10)
          (gfx:path2image (gfx:make-circle (cosr 320 200 (/ i 100))
                                           (sinr 240 200 (/ i 100))
                                           20)
                          layer3
                          '() (list (/ i 5) 0 1 1)))
       (callback (*metro* (+ beat (* .5 1/6))) 'draw-on-layer3 (+ beat 1/6))))

(draw-on-layer3 (*metro* 'get-beat 4))

;; draw video and layer3 transparently into the opengl bitmap
;; then render the opengl bitmap to the canvas
;;
;; You could easily replace
;; (gl:get-image-from-opengl gl) with (gfx:get-code-image)
;; if you didn't want to use any opengl

(define capture-code
    (lambda (time)
       (let ((video (gfx:get-live-frame))
             (opengl (gl:get-image-from-opengl gl)))
          (gfx:image2image video opengl .3)
          (gfx:image2image layer3 opengl 1)
          (gfx:draw-image time canvas opengl .9)
          (objc:release (+ time 5000) opengl video))
       (callback (+ time 2000) 'capture-code (+ time 5000))))

(capture-code (now))

;; start-movie-capture takes a canvas OR an opengl context
;; so you could call (gfx:start-movie-capture gl ...
;; as long as your gl code calls gl:update-backing-image

(gfx:start-movie-capture canvas "~/tmp/my.mov" #t)
;(gfx:stop-movie-capture canvas)