Silverlight & Blend动画设计系列十三：三角函数（Trigonometry）动画之飘落的雪花（Falling Snow）
平时我们所看到的雪花（Falling Snow）飘飘的效果实际上也是一个动画，是由许多的动 画对象共同完成的一个界面效果。对于不同大小的雪片可以通过缩放变换（ScaleTransform ）功能特性确定，雪片飘落是存在于一个空间之中，通过不同的透明度值可使雪花看上去具 有一定的空间视觉，雪花的飘落过程是由三角函数的原理实现的左右滑落效果，并可根据随 机生成数字作为雪花飘落的速度。
雪花UserControl
<Canvas x:Name="LayoutRoot">
<Path Data="F1 M 24.667480,10.681641 L 24.017578,9.555176 L 21.143066,9.555176 L 22.395996,7.384766 L
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24.667480,10.681641 Z" Fill="#FFFFFFFF" Width="24" Height="24" RenderTransformOrigin="0.5,0.5">
<Path.RenderTransform>
<TransformGroup>
<ScaleTransform x:Name="ScaleFlake" ScaleX="1" ScaleY="1"/>
<RotateTransform x:Name="RotateFlake" Angle="0"/>
</TransformGroup>
</Path.RenderTransform>
</Path>
</Canvas>
通过路径（Path）可绘制雪花界面，为此只需要提供一个根据不同参数构造不同的雪花界 面效果的接口，既构造方法：
//根据不同的参数构造雪花对象
public Snowflake(double Left, double Top, double Opacity)
{
InitializeComponent();
//随机速度
Speed = Rand.Next(5);
if (Speed < 1)
{
Speed = 1;
}
//随机位置、弧度、角度
DriftPosition = Left;
DriftRange = Rand.Next(50);
DriftAngle = Rand.Next(270);
Spin = Rand.Next(5);
ScaleFlake.ScaleX = ScaleFlake.ScaleY = Rand.Next(25, 100) / 100.0;
Canvas.SetLeft(this, Left);
Canvas.SetTop(this, Top);
this.Opacity = Opacity;
Position.X = Left;
Position.Y = Top;
}