问题描述
1) 正如标题所说，当我调整窗口大小时，我绘制的对象消失了，但矩形保持原样.
1) As title says, the objects i draw disappear when i resize the window, but the rectangle stays as is.
2) 原点从左上角开始，但我希望它在左下角.
2) The origin starts from the top left, but i wish for it to be at the bottom left.
3) 除了绘图库之外，我找不到任何缩放功能，所以如果我想实现这样的功能，一个选择是通过绘制更大的对象并刷新画布来放大"?
3) I couldn't find any zoom functions, other than in the plot library so if i wish to implement such a thing, one option would to be "zooming" in by drawing bigger objects and refreshing the canvas instead?
(define top-frame (new frame%
[label "KR"]
[width 500]
[height 500]))
;Make a frame by instantiating the frame% class
(define image (pict->bitmap (rectangle 50 50)))
(define canvas (new canvas%
[parent top-frame]
[paint-callback (lambda (canvas dc)
(send dc draw-bitmap image 0 0))]))
(define drawer (send canvas get-dc))
(send top-frame show #t)
; Show the frame by calling its show method
(define (draw-object x)
(sleep/yield 0.1)
(case (first x)
[("LINE") (send drawer draw-line
(second x) (third x)
(fourth x) (fifth x))]
[("CIRCLE") (send drawer draw-bitmap (pict->bitmap (circle (round (fourth x)))) (round (second x)) (round (third x)))]
[("POINT") (send drawer draw-point (round (second x)) (round (third x)))]
[else "Not drawing anything!"]))
(draw-object (find-specific-values (third list-of-objects)))
(map draw-object (map find-specific-values list-of-objects))
推荐答案
ad 1) ...当我调整窗口大小时，我绘制的对象消失了，..."当您调整窗口大小时，系统需要重新绘制窗口的内容.发出重绘事件，最终 Racket GUI 层将调用paint-callback.因此:创建一个可以完成所有绘图的函数.从油漆回调中调用它.在此处查看类似问题:https://stackoverflow.com/a/16086594/23567
ad 1) "...the objects i draw disappear when i resize the window, ..."When you resize a window the system needs to redraw the contents of the window. A redraw event is issued, and eventually the Racket GUI layer will call the paint-callback. Therefore: Make a function that does all the drawing. Call it from the paint-callback. See similar question here: https://stackoverflow.com/a/16086594/23567
ad 2) 一种选择是在绘图上下文中进行坐标变换.请参阅 dc 文档中的 set-transformation.是这样的:
ad 2) One option is to make a coordinate transformation in the drawing context. See set-transformation in the docs for dc<%>. It's someething like this:
(send dc set-transformation
(vector (trans->vector t)
0 0 ; x and y origin
1 -1 ; x and y scale
0)))
y 尺度的 -1 将翻转 y 轴.您可能想要移动原点.
The -1 for the y-scale will flip the y-axis. You might want to move the origin.
ad 3) 缩放可以通过更改 x 和 y 比例，然后重新绘制来完成.你可以试试 1/2 -1/2 的音阶.
ad 3) Zooming can be done by changing the x and y scale, and then redrawing. You can try the scales to 1/2 -1/2 .
这篇关于方案/球拍:画布操作的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！