While the Silverlight Toolkit has made some amazing strides in improving, it still lacks some functionality compared to other toolkit offerings. In particular, Silverlight Toolkit's charts lack splines, or smoothed lines. The idea here is that we don't want the graph to appears as though a line is moving from point to point directly -- that it moves parabolically, or softer.
A typical line series.
Now, this is all fun and games, but can we get something where transitions are more smooth? Yes, we can.
A spline series.
Notice, the spline series changes are more gradual and curved. Are they an entirely accurate representation of the in-between? No, not always -- but they're not meant to be (necessarily).
The Spline Series is literally a copy/paste of the LineSeries, with a few changes. Note that this is located under the Charting/Series folder of the DataVisualization.Toolkit project. Essentially, what we want to do is change the Polyline to a Path. The idea here is that a Polyline doesn't draw Beziers. Below is my (large) code,
SplineSeries.cs:
// (c) Copyright Microsoft Corporation.
// This source is subject to the Microsoft Public License (Ms-PL).
// Please see http://go.microsoft.com/fwlink/?LinkID=131993 for details.
// All other rights reserved.
using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using System.Linq;
using System.Windows.Media;
using System.Windows.Shapes;
#if !DEFINITION_SERIES_COMPATIBILITY_MODE
namespace System.Windows.Controls.DataVisualization.Charting
{
/// <summary>
/// Represents a control that contains a data series to be rendered in X/Y
/// line format.
/// </summary>
/// <QualityBand>Preview</QualityBand>
[StyleTypedProperty(Property = DataPointStyleName, StyleTargetType = typeof(LineDataPoint))]
[StyleTypedProperty(Property = "LegendItemStyle", StyleTargetType = typeof(LegendItem))]
[StyleTypedProperty(Property = "PathStyle", StyleTargetType = typeof(Path))]
[TemplatePart(Name = DataPointSeries.PlotAreaName, Type = typeof(Canvas))]
[SuppressMessage("Microsoft.Maintainability", "CA1501:AvoidExcessiveInheritance", Justification = "Depth of hierarchy is necessary to avoid code duplication.")]
public partial class SplineSeries : LineAreaBaseSeries<LineDataPoint>
{
#region public PointCollection Points
/// <summary>
/// Gets the collection of points that make up the spline.
/// </summary>
public PointCollection Points
{
get { return GetValue(PointsProperty) as PointCollection; }
private set { SetValue(PointsProperty, value); }
}
/// <summary>
/// Identifies the Points dependency property.
/// </summary>
public static readonly DependencyProperty PointsProperty =
DependencyProperty.Register(
"Points",
typeof(PointCollection),
typeof(SplineSeries),
null);
#endregion public PointCollection Points
#region public PathGeometry SplinePoints
/// <summary>
/// Gets the collection of points that make up the line.
/// </summary>
public PathGeometry SplinePoints
{
get { return GetValue(SplinePointsProperty) as PathGeometry; }
private set { SetValue(SplinePointsProperty, value); }
}
/// <summary>
/// Identifies the SplinePoints dependency property.
/// </summary>
public static readonly DependencyProperty SplinePointsProperty =
DependencyProperty.Register(
"SplinePoints",
typeof(PathGeometry),
typeof(SplineSeries),
null);
#endregion public PathGeometry SplinePoints
#region public double SplineTension
/// <summary>
/// Gets or sets the tension in the beziers that make up the spline.
/// </summary>
/// <remarks>
/// The greater the tension, the more straight/linear the spline will look.
/// Less tension creates a more curvy spline.
/// </remarks>
public double SplineTension
{
get { return (double) GetValue(SplineTensionProperty); }
set { SetValue(SplineTensionProperty, value); }
}
/// <summary>
/// Identifies the SplineTension dependency property.
/// </summary>
public static readonly DependencyProperty SplineTensionProperty =
DependencyProperty.Register(
"SplineTension",
typeof(double),
typeof(SplineSeries),
new PropertyMetadata(2.5));
#endregion public double SplineTension
#region public Style PathStyle
/// <summary>
/// Gets or sets the style of the Path object that follows the data
/// points.
/// </summary>
[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Naming", "CA1704:IdentifiersShouldBeSpelledCorrectly", MessageId = "Path", Justification = "Matches System.Windows.Shapes.Path.")]
public Style PathStyle
{
get { return GetValue(PathStyleProperty) as Style; }
set { SetValue(PathStyleProperty, value); }
}
/// <summary>
/// Identifies the PathStyle dependency property.
/// </summary>
[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Naming", "CA1704:IdentifiersShouldBeSpelledCorrectly", MessageId = "Path", Justification = "Matches System.Windows.Shapes.Path.")]
public static readonly DependencyProperty PathStyleProperty =
DependencyProperty.Register(
"PathStyle",
typeof(Style),
typeof(SplineSeries),
null);
#endregion public Style PathStyle
#if !SILVERLIGHT
/// <summary>
/// Initializes the static members of the LineSeries class.
/// </summary>
[SuppressMessage("Microsoft.Performance", "CA1810:InitializeReferenceTypeStaticFieldsInline", Justification = "Dependency properties are initialized in-line.")]
static SplineSeries()
{
DefaultStyleKeyProperty.OverrideMetadata(typeof(SplineSeries), new FrameworkPropertyMetadata(typeof(SplineSeries)));
}
#endif
/// <summary>
/// Initializes a new instance of the LineSeries class.
/// </summary>
public SplineSeries()
{
#if SILVERLIGHT
this.DefaultStyleKey = typeof(SplineSeries);
#endif
}
/// <summary>
/// Acquire a horizontal linear axis and a vertical linear axis.
/// </summary>
/// <param name="firstDataPoint">The first data point.</param>
protected override void GetAxes(DataPoint firstDataPoint)
{
GetAxes(
firstDataPoint,
(axis) => axis.Orientation == AxisOrientation.X,
() =>
{
IAxis axis = CreateRangeAxisFromData(firstDataPoint.IndependentValue);
if (axis == null)
{
axis = new CategoryAxis();
}
axis.Orientation = AxisOrientation.X;
return axis;
},
(axis) => axis.Orientation == AxisOrientation.Y && axis is IRangeAxis,
() =>
{
DisplayAxis axis = (DisplayAxis)CreateRangeAxisFromData(firstDataPoint.DependentValue);
if (axis == null)
{
throw new InvalidOperationException(Properties.Resources.DataPointSeriesWithAxes_NoSuitableAxisAvailableForPlottingDependentValue);
}
axis.ShowGridLines = true;
axis.Orientation = AxisOrientation.Y;
return axis;
});
}
/// <summary>
/// Updates the Series shape object from a collection of Points.
/// </summary>
/// <param name="points">Collection of Points.</param>
protected override void UpdateShapeFromPoints(IEnumerable<Point> points)
{
if (points.Any())
{
PointCollection pointCollection = new PointCollection();
foreach (Point point in points)
{
pointCollection.Add(point);
}
//At least two points are necessary to generate a proper spline
if (pointCollection.Count >= 2)
{
PathGeometry geometry = new PathGeometry();
PathFigure figure = new PathFigure();
PointCollection bezierPoints = GetBezierPoints(pointCollection);
figure.StartPoint = bezierPoints[0];
for (int i = 1; i < bezierPoints.Count; i += 3)
{
figure.Segments.Add(new BezierSegment()
{
Point1 = bezierPoints[i],
Point2 = bezierPoints[i + 1],
Point3 = bezierPoints[i + 2]
});
}
geometry.Figures.Add(figure);
SplinePoints = geometry;
}
else
{
SplinePoints = null;
}
Points = pointCollection;
}
else
{
Points = null;
SplinePoints = null;
}
}
#region Bezier Curve Building
/*
* Formulas and code pulled from Kerem Kat's MapBezier example:
* http://www.codeproject.com/KB/silverlight/MapBezier.aspx
*/
private PointCollection GetBezierPoints(PointCollection pts)
{
PointCollection ret = new PointCollection();
for (int i = 0; i < pts.Count; i++)
{
// for first point append as is.
if (i == 0)
{
ret.Add(pts[0]);
continue;
}
// for each point except first and last get B1, B2. next point.
// Last point do not have a next point.
ret.Add(GetB1(pts, i - 1, SplineTension));
ret.Add(GetB2(pts, i - 1, SplineTension));
ret.Add(pts[i]);
}
return ret;
}
private Point GetB1(PointCollection pts, int i, double a)
{
Point derivedPoint = GetDerivative(pts, i, a);
return new Point(pts[i].X + derivedPoint.X / 3, pts[i].Y + derivedPoint.Y / 3);
}
private Point GetB2(PointCollection pts, int i, double a)
{
Point derivedPoint = GetDerivative(pts, i+1, a);
return new Point(pts[i + 1].X - derivedPoint.X / 3, pts[i + 1].Y - derivedPoint.Y / 3);
}
private Point GetDerivative(PointCollection pts, int i, double a)
{
if (pts.Count < 2)
throw new ArgumentOutOfRangeException("pts", "Data must contain at least two points.");
if (i == 0)
{
// First point.
return new Point((pts[1].X - pts[0].X) / a, (pts[1].Y - pts[0].Y) / a);
}
if (i == pts.Count - 1)
{
// Last point.
return new Point((pts[i].X - pts[i - 1].X) / a, (pts[i].Y - pts[i - 1].Y) / a);
}
return new Point((pts[i + 1].X - pts[i - 1].X) / a, (pts[i + 1].Y - pts[i - 1].Y) / a);
}
#endregion
}
}
#endif
Note that I borrowed my Spline/Bezier code from Kerem Kat's example:
http://www.codeproject.com/KB/silverlight/MapBezier.aspx
Essentially what it does, is takes prior points to adjust such that they curve into the next. The UpdateShapeFromPoints method was changed from the standard LineSeries and uses all of the helper methods that were added to calculate a Bezier curve.
We're pretty much almost done, except for one more minor touch. We need to have the default style included, such that it complies with how Silverlight Toolkit handles it's control templating. We add the following chunk of code to Themes\generic.xaml of the same project:
<!-- charting:SplineSeries -->
<Style TargetType="charting:SplineSeries">
<Setter Property="IsTabStop" Value="False" />
<Setter Property="PathStyle">
<Setter.Value>
<Style TargetType="Path">
<Setter Property="StrokeThickness" Value="2" />
<Setter Property="StrokeMiterLimit" Value="1" />
</Style>
</Setter.Value>
</Setter>
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="charting:SplineSeries">
<Canvas x:Name="PlotArea">
<Path Data="{TemplateBinding SplinePoints}" Stroke="{TemplateBinding Background}" Style="{TemplateBinding PathStyle}"/>
<Polyline Points="{TemplateBinding Points}" />
</Canvas>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
Now, just recompile the Toolkit and you should be good to go!
I've included a "patch" with these files and their updates -- they should be capable of being pasted over their old versions (the Themes\generic.xaml just has the SplineSeries.xaml pasted into it -- I would strongly recommend you doing this with your own source):
https://docs.google.com/viewer?a=v&pid=explorer&chrome=true&srcid=0B9hGvs6yJgfJNzA4YmE1OTctNzNmYy00MzMzLWJhNDQtNTc0M2FlNTA3NzFm&hl=en_US 
