Hi, I try to code a game: I have double buffer and I use thread for refreshing. My method to refresh my canvas: (define (start) (set! PLAY #t) (set! TH (thread (ë() (do () ((not PLAY)) (send my-canvas refresh) (sleep/yield 0.001)))))) And now I have 4 class% : ball (with x y dx dy timer%) target% (just a bitmap) target-destroy% (my target become 3 pieces ( with dx dy ) of initial target bitmap to simulate a destruction when ball is close to target) cannon% (72 bitmaps into a vector for rotation (my cannon follow my mousse)) Now my game has some slow-down !!!!!!! maybe I must use more thread ? a specific bitmap-dc% for each class ? (sorry for my english) thanks!