I'm not seeing laggy behavior when I run your code, but I do see that you're refreshing the entire window on each mouse movement event. Probably you want to make sure that the event isn't a movement even before calling refresh-now. Also, you might want to call refresh instead of refresh-now.
Robby On Mon, Dec 22, 2014 at 3:37 AM, chia kang ren <kangren.c...@gmail.com> wrote: > I wish to draw onto a canvas, select certain objects using a (repaint the > selected objects red) self-implemented select method, and delete them (undo > if done wrongly) with, small misc. features like zooming in and out, > dragging the canvas to view different areas. I've gotten so far as mimicking > a graphical representation of "selecting", but it seems awfully laggy. > Second, the bounding box of "select" disappears if the user holds the mouse > cursor inert. I can remedy this by placing the line drawing functions in > paint-callback, but i don't know if that would be a good idea to do it with > a flag (to differentiate between normal drawing and redrawing selected > items) Also, implementing a select method seems way more complex than i > first thought it would be, although since now i'm at this point, i can > roughly figure out the next few steps would be. > > > 1. A function to calculate all the bounding areas of currently-drawn > objects, then redraw them in red if their coordinates are within the > bounding box of "select". > > 2. Redraw all objects without selected items if delete button pressed. > > > If i am unnecessarily doing anything or looking at the problem the wrong > way, please let me know. Thanks! > > > #lang racket/gui > > (define WIDTH 800) > (define HEIGHT 600) > (define GLOBAL-X-OFFSET 200) > (define GLOBAL-Y-OFFSET 450) > (define X-SCALE 1) > (define Y-SCALE -1) > (define TRANSFORMATION-MATRIX (vector 1 0 0 1 0 0)) > (define ROTATION 0) > (define init-x 0) > (define init-y 0) > (define top-frame (new frame% > [label "KR"] > [width WIDTH] > [height HEIGHT] > [alignment (list 'left 'top)])) > > (define my-canvas% > (class canvas% ; The base class is canvas% > ;; Declare overrides: > (override on-char) > ;; Define overriding method to handle mouse events > (define on-char (lambda (event) > (let ((key (send event get-key-code))) > (case key > ['wheel-up (set! X-SCALE (+ X-SCALE 0.1)) (set! > Y-SCALE (- Y-SCALE 0.1))] > ['wheel-down (set! X-SCALE (- X-SCALE 0.1)) (set! > Y-SCALE (+ Y-SCALE 0.1))]) > (send drawer set-transformation (vector > TRANSFORMATION-MATRIX GLOBAL-X-OFFSET GLOBAL-Y-OFFSET X-SCALE Y-SCALE > ROTATION)) > (send canvas refresh-now)))) > ;; Call the superclass initialization (and pass on all init args) > (define/override (on-event event) > (define x (send event get-x)) > (define y (send event get-y)) > (cond > ((and (send event button-down? 'left) (send event > get-control-down)) > (set! init-x x) > (set! init-y y) > (display (list y (- init-y GLOBAL-Y-OFFSET)))) > ((and (send event button-up? 'left) (send event > get-control-down))) > ;(send drawer draw-line init-x 0 x 0)) > ((and (send event dragging?) (send event get-control-down)) > (let ((start-x (/ (- init-x GLOBAL-X-OFFSET) X-SCALE)) > (start-y (/ (- init-y GLOBAL-Y-OFFSET) Y-SCALE)) > (current-x (/ (- x GLOBAL-X-OFFSET) X-SCALE)) > (current-y (/ (- y GLOBAL-Y-OFFSET) Y-SCALE))) > (send drawer draw-line start-x start-y current-x start-y) > (send drawer draw-line current-x start-y current-x current-y) > (send drawer draw-line current-x current-y start-x current-y) > (send drawer draw-line start-x current-y start-x start-y))) > ((send event button-down? 'left) > (set! init-x x) > (set! init-y y)) > ((send event button-up? 'left) > (set! GLOBAL-X-OFFSET (vector-ref (send drawer > get-transformation) 1)) > (set! GLOBAL-Y-OFFSET (vector-ref (send drawer > get-transformation) 2))) > ((send event dragging?) > (let* ((current-x (- x init-x)) > (current-y (- y init-y))) > (send drawer set-transformation (vector TRANSFORMATION-MATRIX > (+ current-x GLOBAL-X-OFFSET) (+ current-y GLOBAL-Y-OFFSET) X-SCALE Y-SCALE > ROTATION)) > (send canvas refresh-now))))) > (super-instantiate ()))) > > (new button% > [label "Select"] > [parent top-frame]) > (new button% > [label "Select"] > [parent top-frame]) > > (define canvas (new my-canvas% > [parent top-frame] > ;[style (list 'hscroll 'vscroll 'resize-corner)] > [paint-callback (lambda (canvas dc) > (define no-brush (new brush% [style > 'transparent])) > (send drawer set-brush no-brush) > (send drawer draw-line 0 0 200 200) > ;(send drawer draw-line 0 0 0 200) > ;(send drawer draw-line 0 200 200 200) > ;(send drawer draw-line 200 200 200 0) > )])) > (define drawer (send canvas get-dc)) > (send top-frame show #t) > (send drawer set-transformation (vector TRANSFORMATION-MATRIX > GLOBAL-X-OFFSET GLOBAL-Y-OFFSET X-SCALE Y-SCALE ROTATION)) > (sleep/yield 0.1) > > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users > ____________________ Racket Users list: http://lists.racket-lang.org/users
