hello I finally circle the bitmap where I point by mouse but there are several problem 1. the circle filled with white color that I can't see bitmap through the circle 2. the drawn circle didn't erased after I point another coordinates could somebody give me an little advice? my code looks messy and not neat but I paste the code for make it easier to understand #lang scheme (require 2htdp/image racket/gui) (define chipset (make-object bitmap% "town.png" 'png)) (define (check dc m) (define x (send m get-x)) (define y (send m get-y)) (send dc draw-ellipse (- x (modulo x 16)) (- y (modulo y 16)) 16 16)) (define f (new frame% (label "map editor"))) (define xymsg (new message% (label "nth so far") (parent f))) (define select% (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 (m) (send xymsg set-label (string-append "x:" (number->string (send m get-x)) " y:" (number->string (send m get-y)))) (when (send m get-left-down) (check (send this get-dc) m)))) (super-new ) )) (new select% (parent f) (min-width (image-width chipset)) (min-height (image-height chipset)) ) (send f show #t)