WPF画图5000个以上，再画十字线鼠标移动很卡，求解决

代码

Line line1;
Line line2;

private void Main_MouseMove(object sender, MouseEventArgs e)
{
if (line1 != null)
{
main.Children.Remove(line1);
main.Children.Remove(line2);
}
Point p = e.GetPosition(this);
line1 = new Line();
line1.Stroke = Brushes.White;
line1.StrokeThickness = 1;
line1.X1 = 0;
line1.X2 = main.ActualWidth;
line1.Y1 = p.Y;
line1.Y2 = p.Y;
line1.SnapsToDevicePixels = true;
line2 = new Line();
line2.Stroke = Brushes.White;
line2.StrokeThickness = 1;
line2.X1 = p.X;
line2.X2 = p.X;
line2.Y1 = 0;
line2.Y2 = main.ActualHeight;
line2.SnapsToDevicePixels = true;
main.Children.Add(line1);
main.Children.Add(line2);
}

Rectangle rect;
private void button_Click(object sender, RoutedEventArgs e)
{
Random rd = new Random();
for (int i = 0; i < 5000; i++)
{
rect = new Rectangle();
rect.Fill = new SolidColorBrush(Colors.Black);
rect.Stroke = new SolidColorBrush(Colors.White);
rect.Width = 10;
rect.Height = 10;
main_canvas.Children.Add(rect);
Canvas.SetLeft(rect, rd.Next(Convert.ToInt32(main_canvas.ActualWidth)));
Canvas.SetTop(rect, rd.Next(Convert.ToInt32(main_canvas.ActualHeight)));

}

}