Silverlight and bezier curves

Starting to learn Silverlight, so I implemented a simple interface to allow the control points for a Quadratic bezier segment to be controlled via drag-and-drop.


(note it works in Googles chrome, just does not redraw properly)

<UserControl x:Class="DragDrop.Page"
 xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
 xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
 Width="400" Height="300">
 <Grid x:Name="LayoutRoot" Background="White">
  <Canvas>
   <Ellipse x:Name="PointStart" Canvas.Left="100" Canvas.Top="10" Width="20" Height="20" Fill="DarkGreen" Cursor="Hand"/>
   <Ellipse x:Name="PointMiddle" Canvas.Left="200" Canvas.Top="100" Width="20" Height="20" Fill="Black" Cursor="Hand"/>
   <Ellipse x:Name="PointEnd" Canvas.Left="300" Canvas.Top="10" Width="20" Height="20" Fill="DarkRed" Cursor="Hand"/>

   <Path StrokeThickness="10" Canvas.ZIndex="-1" StrokeDashArray="1,1">
    <Path.Stroke>
     <LinearGradientBrush SpreadMethod="Pad">
      <GradientStop Color="DarkGreen" Offset="0"/>
      <GradientStop Color="Black" Offset="0.5"/>
      <GradientStop Color="DarkRed" Offset="1"/>
     </LinearGradientBrush>
    </Path.Stroke>
    <Path.Data>
     <PathGeometry>
      <PathFigure x:Name="Path" StartPoint="100,10">
       <QuadraticBezierSegment x:Name="Segment" Point1="200,100" Point2="300,10" />
      </PathFigure>
     </PathGeometry>
    </Path.Data>
   </Path>
  </Canvas>
 </Grid>
</UserControl>

with C# behind:

namespace DragDrop
{
  public partial class Page : UserControl
  {
    bool isDragging = false;

    public Page()
    {
      InitializeComponent();

      AttachEventHandlers(PointStart);
      AttachEventHandlers(PointMiddle);
      AttachEventHandlers(PointEnd);

      // make sure the bezier reflects our gui control points
      UpdateBezier();
    }

    private void AttachEventHandlers(Ellipse point)
    {
      point.MouseLeftButtonDown += new MouseButtonEventHandler(Point_MouseLeftButtonDown);
      point.MouseLeftButtonUp += new MouseButtonEventHandler(Point_MouseLeftButtonUp);
      point.MouseMove += new MouseEventHandler(Point_MouseMove);
    }

    private void UpdateBezier()
    {
      double radius = this.PointStart.Width / 2;

      Path.StartPoint = Offset(GetPoint(PointStart), radius);
      Segment.Point1 = Offset(GetPoint(PointMiddle), radius);
      Segment.Point2 = Offset(GetPoint(PointEnd), radius);
    }

    private Point Offset(Point inpoint, double offset)
    {
      Point point = new Point(inpoint.X + offset, inpoint.Y + offset);

      return point;
    }

    private static Point GetPoint(DependencyObject sobj)
    {
      Point point = new Point((double)sobj.GetValue(Canvas.LeftProperty), (double)sobj.GetValue(Canvas.TopProperty));

      return point;
    }

    void Point_MouseMove(object sender, MouseEventArgs e)
    {
      if (!isDragging)
        return;

      Ellipse point = sender as Ellipse;
      Point newLocation = e.GetPosition(this);

      MoveShape(point, newLocation);

      UpdateBezier();
    }

    private static void MoveShape(DependencyObject shape, Point newLocation)
    {
      shape.SetValue(Canvas.LeftProperty, newLocation.X);
      shape.SetValue(Canvas.TopProperty, newLocation.Y);
    }

    void Point_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)
    {
      if (!isDragging)
        return;

      isDragging = false;
      Ellipse point = sender as Ellipse;
      point.ReleaseMouseCapture();
    }

    void Point_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
    {
      Ellipse point = sender as Ellipse;
      isDragging = true;
      point.CaptureMouse();
    }
  }
}