如何在球拍中使用鼠标功能？

Question

我正在尝试制作一个文本移动器，即文本将移动到我单击的位置。另外，当我按下“左”键时，我可以改变文本的颜色。我想我已经完成了程序需要的每个部分，但我现在不知道如何将它们组合在一起 :( 我仍然对如何使用鼠标功能感到困惑。这是正文部分的位置：

(require 2htdp/image)
(require 2htdp/universe)
(define POSN-0 (make-posn 50 50))
(define POSN-1 (make-posn 200 200))
(define POSN-2 (make-posn 100 100))
(define (posn-temp p)
  (... (posn-x p) ...
       (posn-y p) ...))

这是颜色部分：

(define Red "red")
(define Black "black")
(define Purple "purple")
(check-expect (RBP Red) "red")
(check-expect (RBP Black) "black")
(check-expect (RBP Purple) "purple")
(define (RBP c)
   (cond
     [(string=? c Red) "red"]
     [(string=? c Black) "black"]
     [(string=? c Purple) "purple"]))

这部分提供了text-mover应用程序所需的所有信息，但我不知道如何使用它？？

(define-struct tm [str pos col])
(define T1(make-tm "apple" 10  "red"))
(define T2(make-tm "banana" 20  "black"))
(define (tm-temp tm)
  (... (tm-str tm) ...
       (tm-pos tm) ...
       (tm-col tm) ...))

待绘制：

(define bg (square 400 "solid" "white"))

(check-expect
 (draw-tm POSN-0)
  (place-image
   (text "POG!"
   25
   "red")
    50 50
     bg))
(define (draw-tm c)
  (place-image
   (text "POG!"
   25
   (RBP c))
    50 50
     bg))

按键：

(define (change-c c ke)
      (cond
        [(key=? ke "left") (RBP c)]
        [else c]))

鼠标上：

(define (move-tm c )
      (cond
        [(mouse=?  )   ]
        [else c]))

大爆炸：

(define (move-text initial-tm)
  (big-bang initial-tm
    [to-draw draw-tm]
    [on-mouse move-tm]
    [on-key change-c]))

Answer 1

阅读on-mouse description: function called with on-mouse has arguments state x y event and different types of mouse events are described in Mouse event docs。在您的情况下，您将需要 "button-up" 或 "drag".

此外，当 x 或 y 或 color 更改时，您必须使用旧实例中的数据创建表示状态的结构的新实例。

这里是示例代码 - 运行它与 (move-text "FooBar")，您可以将显示的文本拖动到新位置或使用 left 键更改颜色。

(require 2htdp/image)
(require 2htdp/universe)

(define-struct text-state [text position color])

(define (next-color color)
  (second (assoc color (list (list "black" "red")
                             (list "red" "purple")
                             (list "purple" "black")))))

(define bg (square 400 "solid" "white"))

(define (draw-state state)
  (place-image
   (text (text-state-text state)
         25
         (text-state-color state))
   (posn-x (text-state-position state))
   (posn-y (text-state-position state))
   bg))

(define (change-color state key)
  (if (key=? key "left")
      (make-text-state (text-state-text state)
                       (text-state-position state)
                       (next-color (text-state-color state)))
      state))

(define (mouse-fn state x y event)
  (if (string=? "drag" event)
      (make-text-state
       (text-state-text state)
       (make-posn x y)
       (text-state-color state))
      state))

(define (move-text text)
  (big-bang (make-text-state text (make-posn 50 50) "black")
    [to-draw draw-state]
    [on-mouse mouse-fn]
    [on-key change-color]))

如何在球拍中使用鼠标功能？

How to use on-mouse function in Racket?

racket