WPF之小米Logo超圆角的实现

某些新闻：小米logo换新，程序员一行代码（border-radius:19px）实现，目前此行代码价值200万

某程序员内心：所以还是因为我代码写太少了，所以这200万才没有我的份吗？

这事儿也成功的引起了本羊的注意，花点时间，咱也用WPF来实现一下，到底这超圆角有多好看？

先上效果图：

经过一番了解，其实本质也就一条数学函数：|x|^n+|y|^n=1，上代码：

 1  public class UIElementHelper
 2     {
 3         public static double GetSuperCornerRadius(FrameworkElement obj)
 4         {
 5             return (double)obj.GetValue(SuperCornerRadiusProperty);
 6         }
 7
 8         public static void SetSuperCornerRadius(FrameworkElement obj, double value)
 9         {
10             obj.SetValue(SuperCornerRadiusProperty, value);
11         }
12
13         public static readonly DependencyProperty SuperCornerRadiusProperty =
14             DependencyProperty.RegisterAttached("SuperCornerRadius", typeof(double), typeof(UIElementHelper), new PropertyMetadata(0.0, new PropertyChangedCallback((s, e) =>
15             {
16                 var n = (double)e.NewValue;
17                 var el = s as FrameworkElement;
18                 if (n == 0)
19                 {
20                     el.Clip = null;
21                 }
22                 else
23                 {
24                     UpdateClip(el);
25                     if (!el.IsLoaded)
26                     {
27                         el.SizeChanged += OnSizeChanged;
28                     }
29                 }
30             })));
31
32         private static void OnSizeChanged(object sender, SizeChangedEventArgs e)
33         {
34             UpdateClip(sender as FrameworkElement, false);
35         }
36
37         private static void UpdateClip(FrameworkElement el, bool updatePoints = true)
38         {
39             if (!updatePoints && el.Clip is StreamGeometry clip && !clip.IsFrozen)
40             {
41                 //
42             }
43             else
44             {
45                 clip = new StreamGeometry();
46                 var points = GetSuperCornerRadiusPoints(GetSuperCornerRadius(el));
47                 using(var context = clip.Open())
48                 {
49                     context.BeginFigure(points[0], true, true);
50                     context.PolyBezierTo(points, true, true);//根据坐标点画贝塞尔曲线
51                 }
52                 points.Clear();
53                 el.Clip = clip;//元素的剪切路径
54             }
55             var group = new TransformGroup();
56             group.Children.Add(new TranslateTransform(1, 1));//WPF以左上角为坐标原点，所以这里进行位移
57             var w = el.RenderSize.Width / 2;
58             group.Children.Add(new ScaleTransform(w, w));//放大
59             clip.Transform = group;
60         }
61
62         /// <summary>
63         /// 计算超圆角路径的坐标点
64         /// </summary>
65         /// <param name="n"></param>
66         /// <returns></returns>
67         public static List<Point> GetSuperCornerRadiusPoints(double n = 3)
68         {
69             var points = new List<Point>();
70             //求出Y>0时坐标
71             for (double x = -1; x <= 1; x += 0.001)
72             {
73                 var y = Math.Pow(1 - Math.Pow(Math.Abs(x), n), 1 / n);//公式：|x|^n+|y|^n=1
74                 points.Add(new Point(x, Math.Round(y, 3)));//3位小数，精度应该足够了
75             }
76             //Y<0的坐标
77             var count = points.Count;
78             for (int i = 1; i < count + 1; i++)
79             {
80                 var p = points[count - i];
81                 points.Add(new Point(p.X, p.Y * -1));
82             }
83             return points;
84         }
85
86
87     }

工程文件，感兴趣的下载玩玩。