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Velocity animation

<Page x:Class="Microsoft.Samples.PerFrameAnimations.FrameIndependentFollowExample"     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">   <Canvas x:Name="containerCanvas" Background="Transparent">     <Rectangle x:Name="followRectangle" Canvas.Left="0" Canvas.Top="0"        Fill="red" Width="50" Height="50" />   </Canvas> </Page> //File:Window.xaml.cs using System; using System.Windows; using System.Windows.Controls; using System.Windows.Data; using System.Windows.Documents; using System.Windows.Media; using System.Windows.Navigation; using System.Windows.Shapes; using System.Windows.Media.Animation; namespace Microsoft.Samples.PerFrameAnimations {     public partial class FrameIndependentFollowExample : Page     {         private Vector _rectangleVelocity = new Vector(0, 0);         private Point _lastMousePosition = new Point(500, 500);         private TimeSpan _lastRender;         public FrameIndependentFollowExample(): base()         {             _lastRender = TimeSpan.FromTicks(DateTime.Now.Ticks);             CompositionTarget.Rendering += UpdateRectangle;         }         private void UpdateRectangle(object sender, EventArgs e)         {             RenderingEventArgs renderArgs = (RenderingEventArgs)e;             Double deltaTime = (renderArgs.RenderingTime - _lastRender).TotalSeconds;             _lastRender = renderArgs.RenderingTime;             Point location = new Point(0,0);             Vector toMouse = _lastMousePosition - location;             double followForce = 1.00;             _rectangleVelocity += toMouse * followForce;             double drag = 0.9;             _rectangleVelocity *= drag;             location += _rectangleVelocity * deltaTime;             Canvas.SetLeft(followRectangle, location.X);             Canvas.SetTop(followRectangle, location.Y);         }     } }