title: Draw a SCNShape with Fill and Outline
body: <p>I already figured how to draw a shape - e.g. a circle with SCNSHape.</p>
  
  <p>Now I want to draw an outline for that shape, so I added a subnode to my circle and tried drawing an outline with the help of the even-odd-file-rule.</p>
  
  <p>This does not work and creates a lot of error messages of the type "SceneKit: error, C3DSourceAccessorCopyDataToAccessor failed" in the console.</p>
  
  <p>What's the best way to create a SCNShape which represens the outline of my circle?</p>
  
  <pre><code>UIBezierPath *strokePath = [UIBezierPath bezierPath];
  strokePath.usesEvenOddFillRule = YES;
  strokePath.lineWidth = 10.0;
  [strokePath addArcWithCenter: CGPointZero radius:  5.0 startAngle: 0.0 endAngle: M_PI * 2.0f clockwise: NO];
  [strokePath addArcWithCenter: CGPointZero radius: 10.0 startAngle: 0.0 endAngle: M_PI * 2.0f clockwise: NO];
  
  SCNShape *strokeShape = [SCNShape shapeWithPath: strokePath extrusionDepth: 0];
  strokeShape.firstMaterial.diffuse.contents = [UIColor blueColor];
  strokeShape.firstMaterial.doubleSided = YES;
  
  SCNNode *strokeNode = [SCNNode nodeWithGeometry: strokeShape];
  </code></pre>