You say NURB I say Poly Quadratic Bezier curves

A small step forward from the last post, to using multi control segment lines.

Looking at PolyQuadraticBezierSegment you might think it allows multiple control points - unfortunately it should really be called QuadraticBezierPolySegments, its a collection of segments with their own distinct control points rather a one segment with multiple control points.

Having said that it still allows you to create:

(use the "+" key to add new segments)

The XAML is very similar, though I have removed the points as they are created dynamically by the C# code now:

<UserControl x:Class="DragDropMulti.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 x:Name="Container">
   <Path StrokeThickness="1" Canvas.ZIndex="-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">
       <PolyQuadraticBezierSegment x:Name="Segment" Points="200,200,300,10" />
      </PathFigure>
     </PathGeometry>
    </Path.Data>
   </Path>
  </Canvas>
 </Grid>
</UserControl>

The class variables have changed to manage a dynamic list of control pointss, and a random generator:

public Page()
{
 InitializeComponent();

 // create first point for start point
 CreateNewPoint();
 // create two control points
 CreateControlPointSet();

 this.KeyUp += new KeyEventHandler(Page_KeyUp);
 // make sure the bezier reflects our gui control points
 UpdateBezier();
}

private void CreateControlPointSet()
{
 CreateNewPoint();
 CreateNewPoint();
}

private void CreateNewPoint()
{
 // create a new circle
 Ellipse ellipse = new Ellipse();
 ellipse.Width = RADIUS * 2;
 ellipse.Height = RADIUS * 2;

 // make it a random colour
 ellipse.Fill = new SolidColorBrush(
  Color.FromArgb(
   255,
   GetRandomColour(),
   GetRandomColour(),
   GetRandomColour()));

 // add it to the interface
 Container.Children.Add(ellipse);

 // put it in a random location
 MoveShape(ellipse, new Point(rand.Next((int)Width), rand.Next((int)Height)));

 // keep a track of them for control points
 ellipses.Add(ellipse);

 // let the user move it, and indicate they can
 AttachEventHandlers(ellipse);
 ellipse.Cursor = Cursors.Hand;
}

private byte GetRandomColour()
{
 return (byte)rand.Next(byte.MaxValue);
}

void Page_KeyUp(object sender, KeyEventArgs e)
{
 if (e.Key == Key.Add)
 {
  CreateControlPointSet();
  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()
{
 this.Path.StartPoint = Offset(GetPoint(ellipses[0]), RADIUS);
 PointCollection points = new PointCollection();

 this.Segment.Points.Clear();
 ellipses.ForEach(ellipse =>
 {
  // not start point (already set as path StartPoint)
  if (ellipse != ellipses[0])
   points.Add(Offset(GetPoint(ellipse), RADIUS));
 });

 // just changing the points in the collection does not work (clear, add)
 // appears to be a bug, so we just replace the whole collection of points
 this.Segment.Points = points;

}

The rest of the code is the same as before for the utility and event handlers. Note the last comment about a bug (by design?) which means making changes to the points collection in place has no effect. I'm thinking bug rather than feature...