How to draw arc with radius and start and stop angle

Question

If I have the following four properties in my DataContext of my Canvas element

Point  Center
double Radius
double StartAngle
double EndAngle

<

Answer 1

May I offer a slightly different solution?

class ArcII:FrameworkElement
{
    /// 

    /// Center point of Arc.
    /// 
    [Category("Arc")]
    public Point Center
    {
        get { return (Point)GetValue(CenterProperty); }
        set { SetValue(CenterProperty, value); }
    }

    // Using a DependencyProperty as the backing store for Center.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty CenterProperty =
        DependencyProperty.Register("Center", typeof(Point), typeof(ArcII), new FrameworkPropertyMetadata(new Point(0, 0), FrameworkPropertyMetadataOptions.AffectsRender));

    /// 

    /// Forces the Arc to the center of the Parent container.
    /// 
    [Category("Arc")]
    public bool OverrideCenter
    {
        get { return (bool)GetValue(OverrideCenterProperty); }
        set { SetValue(OverrideCenterProperty, value); }
    }

    // Using a DependencyProperty as the backing store for OverrideCenter.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty OverrideCenterProperty =
        DependencyProperty.Register("OverrideCenter", typeof(bool), typeof(ArcII), new FrameworkPropertyMetadata((bool)false, FrameworkPropertyMetadataOptions.AffectsRender));

    /// 

    /// Start angle of arc, using standard coordinates. (Zero is right, CCW positive direction)
    /// 
    [Category("Arc")]
    public double StartAngle
    {
        get { return (double)GetValue(StartAngleProperty); }
        set { SetValue(StartAngleProperty, value); }
    }

    // Using a DependencyProperty as the backing store for StartAngle.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty StartAngleProperty =
        DependencyProperty.Register("StartAngle", typeof(double), typeof(ArcII), new FrameworkPropertyMetadata(0.0, FrameworkPropertyMetadataOptions.AffectsRender));

    /// 

    /// Length of Arc in degrees.
    /// 
    [Category("Arc")]
    public double SweepAngle
    {
        get { return (double)GetValue(SweepAngleProperty); }
        set { SetValue(SweepAngleProperty, value); }
    }

    // Using a DependencyProperty as the backing store for SweepAngle.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty SweepAngleProperty =
        DependencyProperty.Register("SweepAngle", typeof(double), typeof(ArcII), new FrameworkPropertyMetadata((double)180, FrameworkPropertyMetadataOptions.AffectsRender));

    /// 

    /// Size of Arc.
    /// 
    [Category("Arc")]
    public double Radius
    {
        get { return (double)GetValue(RadiusProperty); }
        set { SetValue(RadiusProperty, value); }
    }

    // Using a DependencyProperty as the backing store for Radius.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty RadiusProperty =
        DependencyProperty.Register("Radius", typeof(double), typeof(ArcII), new FrameworkPropertyMetadata(10.0, FrameworkPropertyMetadataOptions.AffectsRender));

    [Category("Arc")]
    public Brush Stroke
    {
        get { return (Brush)GetValue(StrokeProperty); }
        set { SetValue(StrokeProperty, value); }
    }

    // Using a DependencyProperty as the backing store for Stroke.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty StrokeProperty =
        DependencyProperty.Register("Stroke", typeof(Brush), typeof(ArcII), new FrameworkPropertyMetadata((Brush)Brushes.Black,FrameworkPropertyMetadataOptions.AffectsRender));

    [Category("Arc")]
    public double StrokeThickness
    {
        get { return (double)GetValue(StrokeThicknessProperty); }
        set { SetValue(StrokeThicknessProperty, value); }
    }

    // Using a DependencyProperty as the backing store for StrokeThickness.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty StrokeThicknessProperty =
        DependencyProperty.Register("StrokeThickness", typeof(double), typeof(ArcII), new FrameworkPropertyMetadata((double)1,FrameworkPropertyMetadataOptions.AffectsRender));

    protected override void OnRender(DrawingContext dc)
    {
        base.OnRender(dc);
        Draw(dc);
    }

    private void Draw(DrawingContext dc)
    {
        Point center = new Point();
        if (OverrideCenter)
        {
            Rect rect = new Rect(RenderSize);
            center = Polar.CenterPointFromRect(rect);
        }
        else
        {
            center = Center;
        }

        Point startPoint = Polar.PolarToCartesian(StartAngle, Radius, center);
        Point endPoint = Polar.PolarToCartesian(StartAngle + SweepAngle, Radius, center);
        Size size = new Size(Radius, Radius);

        bool isLarge = (StartAngle + SweepAngle) - StartAngle > 180;

        List segments = new List(1);
        segments.Add(new ArcSegment(endPoint, new Size(Radius, Radius), 0.0, isLarge, SweepDirection.Clockwise, true));

        List figures = new List(1);
        PathFigure pf = new PathFigure(startPoint, segments, true);
        pf.IsClosed = false;
        figures.Add(pf);
        Geometry g = new PathGeometry(figures, FillRule.EvenOdd, null);

        dc.DrawGeometry(null, new Pen(Stroke,StrokeThickness), g);
    }
}

Usage:

Notes: A) This will not do a 360 SweepAngle, for that use an ellipse. B) OverrideCenter: This puts the center of the Arc in the center of its parent. Note that elements like a Grid that can be partitioned, still have a center, which may not be the column or row the Arc is in.