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。