omg it works!! thank you! although I am satisfied with this method, do you know the better way for it? , Richard Cleis <rcleis@mac.com>還戚拙失: > Insert the two lines below to see that what you want is possible, but I doubt such a quick hack is the right way to do it. > > > > rac > > > > On Oct 27, 2010, at 8:48 PM, kty1104@gmail.com wrote: > > > > > 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) > > > > > >  (send dc draw-bitmap chipset 0 0) > >  (send dc set-brush "blue" 'transparent) > > > > > > > > > (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 (ル () (send (send this get-dc) draw-bitmap chipset 0 0))) > > > (define on-event (ル (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)_________________________________________________ > > > For list-related administrative tasks: > > > http://lists.racket-lang.org/listinfo/users > > > >