<Window.Resources>  
     <!--外-->
        <Storyboard x:Key="Storyboard1" RepeatBehavior="Forever">
            <PointAnimationUsingKeyFrames Storyboard.TargetProperty="(Shape.Stroke).(LinearGradientBrush.StartPoint)" 
                                          Storyboard.TargetName="rectangle">
                <EasingPointKeyFrame KeyTime="0:0:0.5" Value="0.855,0.148"/>
                <EasingPointKeyFrame KeyTime="0:0:1" Value="0.852,0.855"/>
                <EasingPointKeyFrame KeyTime="0:0:1.5" Value="0.148,0.855"/>
                <EasingPointKeyFrame KeyTime="0:0:2" Value="0.144,0.149"/>
                <EasingPointKeyFrame KeyTime="0:0:2.5" Value="0,0"/>

            </PointAnimationUsingKeyFrames>
            <PointAnimationUsingKeyFrames Storyboard.TargetProperty="(Shape.Stroke).(LinearGradientBrush.EndPoint)" 
                                          Storyboard.TargetName="rectangle">
                <EasingPointKeyFrame KeyTime="0:0:0.5" Value="0.145,0.852"/>
                <EasingPointKeyFrame KeyTime="0:0:1" Value="0.148,0.145"/>
                <EasingPointKeyFrame KeyTime="0:0:1.5" Value="0.852,0.145"/>
                <EasingPointKeyFrame KeyTime="0:0:2" Value="0.856,0.851"/>
                <EasingPointKeyFrame KeyTime="0:0:2.5" Value="0,1"/>

            </PointAnimationUsingKeyFrames>
        </Storyboard>
     <!--中-->
        <Storyboard x:Key="Storyboard2" RepeatBehavior="Forever">
            <PointAnimationUsingKeyFrames Storyboard.TargetProperty="(Shape.Stroke).(LinearGradientBrush.StartPoint)" 
                                          Storyboard.TargetName="rectangle1">
                <EasingPointKeyFrame KeyTime="0:0:0.5" Value="0.855,0.148"/>
                <EasingPointKeyFrame KeyTime="0:0:1" Value="0.852,0.855"/>
                <EasingPointKeyFrame KeyTime="0:0:1.5" Value="0.148,0.855"/>
                <EasingPointKeyFrame KeyTime="0:0:2" Value="0.144,0.149"/>
                <EasingPointKeyFrame KeyTime="0:0:2.5" Value="0,0"/>

            </PointAnimationUsingKeyFrames>
            <PointAnimationUsingKeyFrames Storyboard.TargetProperty="(Shape.Stroke).(LinearGradientBrush.EndPoint)" 
                                          Storyboard.TargetName="rectangle1">
                <EasingPointKeyFrame KeyTime="0:0:0.5" Value="0.145,0.852"/>
                <EasingPointKeyFrame KeyTime="0:0:1" Value="0.148,0.145"/>
                <EasingPointKeyFrame KeyTime="0:0:1.5" Value="0.852,0.145"/>
                <EasingPointKeyFrame KeyTime="0:0:2" Value="0.856,0.851"/>
                <EasingPointKeyFrame KeyTime="0:0:2.5" Value="0,1"/>

            </PointAnimationUsingKeyFrames>
        </Storyboard>
     <!--內-->
        <Storyboard x:Key="Storyboard3" RepeatBehavior="Forever">
            <PointAnimationUsingKeyFrames Storyboard.TargetProperty="(Shape.Stroke).(LinearGradientBrush.StartPoint)" 
                                          Storyboard.TargetName="rectangle2">
                <EasingPointKeyFrame KeyTime="0:0:0.5" Value="0.855,0.148"/>
                <EasingPointKeyFrame KeyTime="0:0:1" Value="0.852,0.855"/>
                <EasingPointKeyFrame KeyTime="0:0:1.5" Value="0.148,0.855"/>
                <EasingPointKeyFrame KeyTime="0:0:2" Value="0.144,0.149"/>
                <EasingPointKeyFrame KeyTime="0:0:2.5" Value="0,0"/>

            </PointAnimationUsingKeyFrames>
            <PointAnimationUsingKeyFrames Storyboard.TargetProperty="(Shape.Stroke).(LinearGradientBrush.EndPoint)" 
                                          Storyboard.TargetName="rectangle2">
                <EasingPointKeyFrame KeyTime="0:0:0.5" Value="0.145,0.852"/>
                <EasingPointKeyFrame KeyTime="0:0:1" Value="0.148,0.145"/>
                <EasingPointKeyFrame KeyTime="0:0:1.5" Value="0.852,0.145"/>
                <EasingPointKeyFrame KeyTime="0:0:2" Value="0.856,0.851"/>
                <EasingPointKeyFrame KeyTime="0:0:2.5" Value="0,1"/>

            </PointAnimationUsingKeyFrames>
        </Storyboard>
    </Window.Resources>
    <Window.Triggers>
        <!--外-->
        <EventTrigger RoutedEvent="FrameworkElement.Loaded">
            <BeginStoryboard Storyboard="{StaticResource Storyboard1}"/>
        </EventTrigger>
        <!--中-->
        <EventTrigger RoutedEvent="FrameworkElement.Loaded">
            <BeginStoryboard Storyboard="{StaticResource Storyboard2}"/>
        </EventTrigger>
        <!--內-->
        <EventTrigger RoutedEvent="FrameworkElement.Loaded">
            <BeginStoryboard Storyboard="{StaticResource Storyboard3}"/>
        </EventTrigger>
    </Window.Triggers>
    <Grid> 
        <!--外-->
        <Rectangle x:Name="rectangle" Width="300" Height="300" 
                   StrokeThickness="3">
            <Rectangle.Stroke>
                <LinearGradientBrush  Opacity="0.6">
                    <GradientStop Color="Transparent" Offset="0"/>
                    <GradientStop Color="Violet"  Offset="1"/>
                </LinearGradientBrush>
            </Rectangle.Stroke>

        </Rectangle>
        <!--中-->
        <Rectangle x:Name="rectangle1" Width="200" Height="200" 
                   StrokeThickness="3">
            <Rectangle.Stroke>
                <LinearGradientBrush  Opacity="0.6">
                    <GradientStop Color="Transparent" Offset="0"/>
                    <GradientStop Color="Green"  Offset="1"/>
                </LinearGradientBrush>
            </Rectangle.Stroke>

        </Rectangle>
        <!--內-->
        <Rectangle x:Name="rectangle2" Width="100" Height="100" 
                   StrokeThickness="3">
            <Rectangle.Stroke>
                <LinearGradientBrush  Opacity="0.6">
                    <GradientStop Color="Transparent" Offset="0"/>
                    <GradientStop Color="red"  Offset="1"/>
                </LinearGradientBrush>
            </Rectangle.Stroke>

        </Rectangle>

    </Grid>