[racket] newb: implementation of select items

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.chia at 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)
>
>
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