套餐套餐(球拍)

Question

我正在尝试设计一个名为add-frame的函数，它接受一张图像，并在所有四个边都用一个像素的黑色边框包围它。这就是我所拥有的：

(define (horizontal-line x)
(line x 0 "black"))

(define (vertical-line x)
(line 0 x "black"))

(define (add-left-border height design color)
  (overlay/align "left" "top"
                 (vertical-line height)
                 (square height design color)))

(define (add-right-border height design color)
  (overlay/align "right" "top"
                 (vertical-line height)
                 (square height design color)))

(define (add-top-border height design color)
  (overlay/align "right" "top"
                 (horizontal-line height)
                 (square height design color)))

(define (add-bottom-border height design color)
  (overlay/align "right" "bottom"
                 (horizontal-line height)
                 (square height design color)))

(define (add-frame height design color)
  (overlay (square height design color)
           (add-left-border height design color)
           (add-right-border height design color)
           (add-top-border height design color)
           (add-bottom-border height design color)))

当我运行"add-frame“时，返回的是一个只有左边框的正方形图像。如何使边框的其余部分显示在返回的正方形上？

Answer 1

此表达式

(overlay/align "left" "top"
               (vertical-line height)
               (square height design color))

将正确地在正方形的左侧添加一条垂直线。

这是一个表达式

(overlay/align "right" "top"
               (vertical-line height)
               (square height design color))

将正确地在正方形的右侧添加一条垂直线。

然而，如果你把这两个图像放在一起，那么由于它们的大小相同，你只能看到顶部的那个。

要解决这个问题(部分地)，你可以在正方形的另一边添加一条透明线。

更好的解决方案是传递要添加线条的图像。

也就是说，将add-left-border更改为：

(define (add-left-border height design color image)
  (overlay/align "left" "top"
                 (vertical-line height)
                 image))

这将在图像顶部添加左侧边框。

如下所示：

(define (horizontal-line x)
  (line x 1 "black"))

(define (vertical-line x)
  (line 1 x "black"))

(define (add-left-border height design color image)
  (overlay/align "left" "top"
                 (vertical-line height)
                 image))

(define (add-right-border height design color image)
  (overlay/align "right" "top"
                 (vertical-line height)
                 image))

(add-left-border 80 "solid" "red"
                 (add-right-border 80 "solid" "red"
                                   (circle 40 "solid" "red")))

注意:最好在镜像上使用image-width和image-height，以便自动获得正确的大小。