hi , What's the best between : (define MY-CANVAS% (class canvas% (init-field (buff (make-object bitmap% 1000 1000)) (Dbuffer (new bitmap-dc% [bitmap buff ] )) (bitmap1 (make-object bitmap% "test.jpg"))) (inherit get-dc) (define/override (refresh) (send Dbuffer clear) (send Dbuffer draw-bitmap bitmap1 0 0 'solid ) (send (get-dc) draw-bitmap Dbuffer 0 0)) (define/override (on-paint) (send this refresh)) (super-new))) or like this: (define buff (make-object bitmap% 1000 1000)) (define Dbuffer (new bitmap-dc% (bitmap buff))) (define bitmap1 (make-object bitmap% "test.jpg")) (define canvas (new canvas% (parent FRAME) (paint-callback (ë (c dc) (send Dbuffer clear) (send Dbuffer draw-bitmap bitmap1 0 0 'solid ) (send dc draw-bitmap Dbuffer 0 0))))) I get the same result, but whicth method I must use ? What is the most conventional?