如何在 Canvas 上画一个圆圈？

Question

我是 WPF 的新手，正在做 MyPaint 应用程序。 当我在画布上画一个圆或一个正方形时，当​​我沿着 Oy 轴移动鼠标时，它们会跟随我的鼠标。 我不知道如何解决这个问题。 这里是。 感谢阅读。

Point p1, p2;
        Point currClick;
        //int i = 0;
        //private bool flag = true;
        Rectangle Myline;

        SolidColorBrush scb = new SolidColorBrush(Colors.Black);
private void MyCanvas_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
        {
            p1 = e.GetPosition(MyCanvas);
            Myline = new Rectangle();

            Myline.Stroke = scb;
            Myline.StrokeThickness = 1;
            DoubleCollection Mydash = new DoubleCollection { 5, 3 };
            Myline.StrokeDashArray = Mydash;
            Canvas.SetLeft(Myline, p1.X);
            Canvas.SetTop(Myline, p1.Y);
            //Myline.Fill = scb;


            MyCanvas.Children.Add(Myline);

        }
private void MyCanvas_MouseMove_1(object sender, System.Windows.Input.MouseEventArgs e)
{
            if (e.LeftButton == MouseButtonState.Released)
            {
                return;
            }
else
            {
                Myline.Width = Math.Max(p2.X, p1.X) - Math.Min(p2.X, p1.X);
                Myline.Height = Myline.Width;
                Canvas.SetLeft(Myline, Math.Min(p1.X, p2.X));
                Canvas.SetTop(Myline, Math.Min(p1.Y, p2.Y));
            }
        }

Answer 1

像这样改变鼠标移动事件：

 private void MyCanvas_MouseMove_1(object sender, System.Windows.Input.MouseEventArgs e)
    {
        p2 = e.GetPosition(MyCanvas);
        if (e.LeftButton == MouseButtonState.Pressed)
        {
            if (p1.X < p2.X)
                Canvas.SetLeft(Myline, p1.X);  else Canvas.SetLeft(Myline, p2.X);
            if (p1.Y < p2.Y)
                Canvas.SetTop(Myline, p1.Y);  else Canvas.SetTop(Myline, p2.Y);

            Myline.Width = Math.Max(p2.X, p1.X) - Math.Min(p2.X, p1.X);
            Myline.Height = Math.Max(p2.Y, p1.Y) - Math.Min(p2.Y, p1.Y);
       }
    }