WPF 实现雪花效果

雪花控件类：
class MM:Control
    {
        DispatcherTimer dispatcherTimer = new DispatcherTimer();
        public MM()
        {
            dispatcherTimer.Interval = TimeSpan.FromMilliseconds(100); ;
            dispatcherTimer.Tick += DispatcherTimer_Tick;
            dispatcherTimer.Start();
        }

        private void DispatcherTimer_Tick(object sender, EventArgs e)
        {
            this.InvalidateVisual();
        }

        protected override void OnRender(DrawingContext drawingContext)
        {
            var currentcolor = Colors.White;
            Brush brush = new RadialGradientBrush(currentcolor,
                    Color.FromArgb(0, currentcolor.R, currentcolor.G, currentcolor.B));
            Random r = new Random();

            for (int i = 0; i < 530; i++)
            {
                var w = 35 * r.NextDouble();
                var rect =
                new RectangleGeometry(
                    new Rect(new Point(r.Next(10,(int)this.Width), r.Next(10, (int)this.Height)),
                        new Size(w, w)));
                drawingContext.DrawGeometry(brush, null, rect);
            }
            
        }
    }

前台代码：
<Window x:Class="WpfAppTest.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfAppTest"
        mc:Ignorable="d"  WindowStyle="None" AllowsTransparency="True" Top="100" Left="100"
        Title="MainWindow" Height="450" Width="800">
    <Window.Background>
        <LinearGradientBrush StartPoint="0,0" EndPoint="0,1">
            <GradientStop Color="#05438C" Offset="0"/>
            <GradientStop Color="White" Offset="0.9"/>
            <GradientStop Color="White" Offset="1"/>
        </LinearGradientBrush>
    </Window.Background>
    <local:MM x:Name="cc" HorizontalAlignment="Left" Height="417.114"  VerticalAlignment="Top" Width="791.112" RenderTransformOrigin="0.5,0.5" Margin="0,0.007,0,0">
        <local:MM.RenderTransform>
            <TransformGroup>
                <ScaleTransform/>
                <SkewTransform/>
                <RotateTransform Angle="0.387"/>
                <TranslateTransform/>
            </TransformGroup>
        </local:MM.RenderTransform>
    </local:MM>
</Window>

实现效果：