SpinnerControl.xaml

<UserControl x:Class="PhantomUI.SpinnerControl"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
             xmlns:phantomUi="clr-namespace:PhantomUI"
             mc:Ignorable="d" 
             d:DesignHeight="300" d:DesignWidth="300">
    <UserControl.Resources>
        <Storyboard x:Key="Storyboard">
            <DoubleAnimation Storyboard.TargetName="ellipse"
                       Storyboard.TargetProperty="(UIElement.RenderTransform).(TransformGroup.Children)[2].(RotateTransform.Angle)"
                       From="0" To="360" Duration="00:00:01"
                       RepeatBehavior="Forever"/>
            <ColorAnimationUsingKeyFrames Storyboard.TargetProperty="(Shape.Fill).(SolidColorBrush.Color)" Storyboard.TargetName="ellipse">
                <EasingColorKeyFrame KeyTime="0" Value="Black"/>
            </ColorAnimationUsingKeyFrames>
        </Storyboard>
    </UserControl.Resources>
    <UserControl.Triggers>

        <EventTrigger RoutedEvent="phantomUi:SpinnerControl.StartAnimation">
            <BeginStoryboard Storyboard="{StaticResource Storyboard}" Name="MyStoryBoard"/>
        </EventTrigger>
        
        <EventTrigger RoutedEvent="phantomUi:SpinnerControl.StopAnimation">
            <StopStoryboard BeginStoryboardName="MyStoryBoard"></StopStoryboard>
        </EventTrigger>        
      
    </UserControl.Triggers>
    <Grid>
        <Ellipse x:Name="ellipse" Fill="Black" RenderTransformOrigin="0.5,0.5">
            <Ellipse.RenderTransform>
                <TransformGroup>
                    <ScaleTransform/>
                    <SkewTransform/>
                    <RotateTransform/>
                    <TranslateTransform/>
                </TransformGroup>
            </Ellipse.RenderTransform>
            <Ellipse.OpacityMask>
                <ImageBrush ImageSource="media/spinnermask.png"/>
            </Ellipse.OpacityMask>
        </Ellipse>
    </Grid>
</UserControl>