[plt-scheme] Re: Draw and save coordinates on every mouse event on canvas?

oppss..I am sorry that I forgot to answer your question :( That
warning is written in document of "draw.ss".

regards.

On Jun 11, 1:55 am, Matthias Felleisen <matth... at ccs.neu.edu> wrote:
> Here is a solution:
>
> #lang scheme
>
> (require 2htdp/universe)
>
> ;; World = [Listof (list Nat Nat)]
> (define mt (empty-scene 200 200))
> (define col "red")
> (define DOT (circle 3 "solid" col))
>
> (define (click w x y ke)
>    (cond
>      [(mouse=? "button-down" ke)
>       (cons (list x y) w)]
>      [else w]))
>
> (define (render w0)
>    (local ((define (cnt w a) (foldl (lambda (f a) (list f (apply ln+  
> f a))) a w))
>            (define (dot s p) (place-image DOT (first p) (second p) s))
>            (define (ln+ p q s)
>              (add-line s (first p) (second p) (first q) (second q) col))
>            (define dots (foldr (lambda (f r) (dot r f)) mt w0)))
>      (cond
>        [(empty? w0) mt]
>        [else (second (cnt (rest w0) (list (first w0) (dot dots (first  
> w0)))))])))
>
> (big-bang '() (on-mouse click) (on-draw render))
>
> But this solution will give you away in case this is homework. To  
> prove that this isn't homework, you need to point us to the place  
> where our manuals recommend using world.ss.
>
> -- Matthias
>
> On Jun 10, 2009, at 6:53 AM, Captain___nemo wrote:
>
>
>
>
>
> > Hi,
> > I am newbie in scheme, just started yesterday. So, please don't mind
> > if I am overlooking anything simple.
>
> > I want to draw circular points on every click on the drawing window
> > (or canvas). Also I want to save the coordinates in an array. After
> > every click a connecting line should be drawn (from last point) and so
> > on.
>
> > Now, I don't understand how I should put a canvas. As I can see in
> > Dr.Scheme manual , it is recommended to use world.ss.  But I don't
> > understand how will I get the coordinates and save in an array? Also
> > how that line can be drawn?
>
> > Any suggestion is appreciated.
>
> > Thanks in advance.
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