WPF中的动画——（五）路径动画

路径动画是一种专门用于将对象按照指定的Path移动的动画，虽然我们也可以通过控制动画的旋转和偏移实现对象的移动，但路径动画更专业，它的实现更加简洁明了。

路径动画中最常用的是MatrixAnimationUsingPath，它通常用于控制对象的MatrixTransform，一个简单的例子如下： 

 1     <Canvas >

 2         <Canvas.Resources>

 3             <PathGeometry x:Key="path" Figures="M 10,100 C 35,0 135,0 160,100 180,190 285,200 310,100" />

 4             <Storyboard x:Key="pathStoryboard" >

 5                 <MatrixAnimationUsingPath PathGeometry="{StaticResource path}"

 6                                           Storyboard.TargetName="ButtonMatrixTransform"

 7                                           Storyboard.TargetProperty="Matrix"

 8                                           DoesRotateWithTangent="True"

 9                                           Duration="0:0:5" RepeatBehavior="Forever" >

10                 </MatrixAnimationUsingPath>

11             </Storyboard>

12         </Canvas.Resources>

13         

14         <Canvas.Triggers>

15             <EventTrigger RoutedEvent="Control.Loaded">

16                 <BeginStoryboard Storyboard="{StaticResource pathStoryboard}" />

17             </EventTrigger>

18         </Canvas.Triggers>

19         

20         <Path Data="{StaticResource path}" Stroke="Black" StrokeThickness="1" />

21         

22         <Button Width="50" Height="20" >

23             <Button.RenderTransform>

24                 <MatrixTransform x:Name="ButtonMatrixTransform" />

25             </Button.RenderTransform>

26         </Button>

27     </Canvas>

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注意这儿有一个DoesRotateWithTangent的属性，设置上它后，对象在移动的过程中还能根据路径的坡度旋转，非常有用。

除了MatrixAnimationUsingPath外，另外还有两种路径动画：PointAnimationUsingPath和DoubleAnimationUsingPath。PointAnimationUsingPath用于靠中心点确定位置的形状， 

 1     <Canvas >

 2         <Canvas.Resources>

 3             <PathGeometry x:Key="path" Figures="M 10,100 C 35,0 135,0 160,100 180,190 285,200 310,100" />

 4             <Storyboard x:Key="pathStoryboard" >

 5                 <PointAnimationUsingPath PathGeometry="{StaticResource path}"

 6                                           Storyboard.TargetName="ellipse"

 7                                           Storyboard.TargetProperty="Center"

 8                                           Duration="0:0:5" RepeatBehavior="Forever" >

 9                 </PointAnimationUsingPath>

10             </Storyboard>

11         </Canvas.Resources>

12         

13         <Canvas.Triggers>

14             <EventTrigger RoutedEvent="Control.Loaded">

15                 <BeginStoryboard Storyboard="{StaticResource pathStoryboard}" />

16             </EventTrigger>

17         </Canvas.Triggers>

18         

19         <Path Data="{StaticResource path}" Stroke="Black" StrokeThickness="1" />

20         

21         <Path Fill="Orange">

22             <Path.Data>

23                 <EllipseGeometry x:Name="ellipse" Center="5,5" RadiusX="12" RadiusY="12"/>

24             </Path.Data>

25         </Path>

26     </Canvas>

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 DoubleAnimationUsingPath则是通过X、Y和Angle三个属性联合实现路径的变化，一般在TranslateTransform中使用，如下就是一个简单的例子： 

 1     <Canvas >

 2         <Canvas.Resources>

 3             <PathGeometry x:Key="path" Figures="M 10,100 C 35,0 135,0 160,100 180,190 285,200 310,100" />

 4             <Storyboard x:Key="pathStoryboard" >

 5                 <DoubleAnimationUsingPath PathGeometry="{StaticResource path}"

 6                                           Storyboard.TargetName="translateTransform"

 7                                           Storyboard.TargetProperty="X"

 8                                           Source="X"

 9                                           Duration="0:0:5" RepeatBehavior="Forever" >

10                 </DoubleAnimationUsingPath>

11                 <DoubleAnimationUsingPath PathGeometry="{StaticResource path}"

12                                           Storyboard.TargetName="translateTransform"

13                                           Storyboard.TargetProperty="Y"

14                                           Source="Y"

15                                           Duration="0:0:5" RepeatBehavior="Forever" >

16                 </DoubleAnimationUsingPath>

17             </Storyboard>

18         </Canvas.Resources>

19         

20         <Canvas.Triggers>

21             <EventTrigger RoutedEvent="Control.Loaded">

22                 <BeginStoryboard Storyboard="{StaticResource pathStoryboard}" />

23             </EventTrigger>

24         </Canvas.Triggers>

25         

26         <Path Data="{StaticResource path}" Stroke="Black" StrokeThickness="1" />

27         

28         <Path Fill="Orange">

29             <Path.Data>

30                 <EllipseGeometry x:Name="ellipse" Center="5,5" RadiusX="12" RadiusY="12"/>

31             </Path.Data>

32             <Path.RenderTransform>

33                 <TranslateTransform x:Name="translateTransform" />

34             </Path.RenderTransform>

35         </Path>

36     </Canvas>

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 这个实现的效果和MatrixAnimationUsingPath类似，但比它用法复杂，很难找到它的使用场景，但由于它的控制维度更多，可能一般用于需要更多的控制的地方吧。