我正在尝试SCNShape使用以下代码来绘制一块馅饼：
UIBezierPath *piePiece = [UIBezierPath bezierPath];
[piePiece addArcWithCenter: CGPointZero radius: 0.150 startAngle: 0.0 endAngle: M_PI/6 clockwise: YES];
[piePiece closePath];
SCNShape *pieShape = [SCNShape shapeWithPath: piePiece extrusionDepth: 0];
pieShape.firstMaterial.diffuse.contents = [UIColor blueColor];
pieShape.firstMaterial.doubleSided = YES;
SCNNode *pieNode = [SCNNode nodeWithGeometry: pieShape];
但我得到以下形状：
样本 我看不到弧线。我究竟做错了什么？
谢谢
