hello~ I am making map editor one of the editor's ability is select tile image from chip-set(kind of town map tile) image and circle the selected tile I made a following code but I don't think that this is good way to update image and it doesn't working properly as well. could somebody give me an little advice? #lang scheme/gui (require 2htdp/image) (define pic dc<%>) (define chipset (make-object bitmap% "town.png" 'png)) (define f (instantiate frame% ("map editor"))) (define mcan% (class canvas% (override on-event on-paint) (define on-paint (ë () (send (send this get-dc) draw-bitmap chipset 0 0))) (define on-event (ë (e) (send msg set-label (string-append (number->string (floor (/ (send e get-x) 16))) " " (number->string (floor (/ (send e get-y) 16))))) (when (send e get-left-down) (begin (set! chipset (place-image (circle 8 "outline" "orange") (send e get-x) (send e get-y) chipset)) (send f refresh)));it doesn't seems to good way )) (super-instantiate ()))) (define mcan (new mcan% (parent f) (min-width (image-width chipset)) (min-height (image-height chipset)))) (define msg (instantiate message% ("nothing so far" f))) (define tile-width-field (instantiate text-field% ("width") (init-value "16") (parent f) (stretchable-width #f))) (define tile-height-field (instantiate text-field% ("height") (init-value "16") (parent f) (stretchable-width #f))) (send f show #t)