s c h e m a t i c s : c o o k b o o k

;; obtain a bitmap and stick it into a bitmap dc
(define plt
  (make-object bitmap% (build-path (collection-path "icons") 
                                   "plt.gif")))
(define bm
  (new bitmap-dc% [bitmap plt]))

;; --- set up a frame with a canvas in which to display this image
(define frame
  (new frame% [label "Test for Linda"]
       [width (send plt get-width)] [height (send plt get-height)]))

(define canvas (new
                ;; --- create a class on the fly that overrides the callback for
                ;; --- mouse events in a canvas; you could name it, if needed
                (class canvas%
                  ;; Event -> Void
                  ;; act on each mouse event
                  (define/override (on-event e)
                    (define kind (send e button-down?))
                    (define x (send e get-x))
                    (define y (send e get-y))
                    (define c (new color%))
                    (when kind
                      (if (send bm get-pixel x y c)
                          (printf "color is ~s ~s ~s\n"
                                  (send c red) (send c green) (send c blue))
                          (printf "no color"))))
                  (super-new))
                ;;--- provide a frame and a paint method for displaying plt.gif
                [parent frame]
                [paint-callback (lambda (e dc) (send dc draw-bitmap plt 0 0))]))

;; --- run program run
(send frame show #t)