Question

I am trying to draw a figure something like this:

I need to have a unique element for each arc segment that I can handle events on and recolor as I need. I am a bit unsure on how to create the proper geometries in WPF. I can easily calculate the four points for each arc segment from the radius of the circles and the angle from center. Using a radius of 100 for the outer circle and 50 for the inner, the four points in red are (clockwise from top left with origin at top of circle):

0,0
70,30
35,65
0,50

Using these points I create a simple path to draw the segment:

<Path Stroke="Black" Fill="Black" StrokeThickness="1" >
  <Path.Data>
    <PathGeometry>
      <PathGeometry.Figures>
        <PathFigure StartPoint="0,0">
          <PathFigure.Segments>
            <ArcSegment Point="70,30" />
            <LineSegment Point="35,65" />
            <ArcSegment Point="0,50" />
          </PathFigure.Segments>
        </PathFigure>
      </PathGeometry.Figures>
    </PathGeometry>
  </Path.Data>
</Path>

But that just draws a trapezoid with straight lines. I know I can alter the Size on the ArcSegments, but I can’t seem to figure out how that affects the curvature. I want the arcs to follow the main circle, but I am not sure how to express that. How can I make the arcs have the right curvature?

Also, how do I express and add paths in the c# code behind,rather than in the xaml?

Answer 1

I’ve drawn exactly that sort of shape (two coaxial arcs and two radials joining them) like this:

new LineSegment(new Point(x2, y2), true),
new ArcSegment(new Point(x3,y3),new Size(100*outerRadius,100*outerRadius), 0,largeAngle, SweepDirection.Clockwise, true),
new LineSegment(new Point(x4, y4), true),
new ArcSegment(new Point(x1, y1),new Size(100*innerRadius,100*innerRadius), 0,largeAngle, SweepDirection.Counterclockwise, true),

Obviously that’s code rather than XAML, but it might give you a kick-start.