如何将SkPhysicsBody添加到半圆

Question

我无法将SKPhysicsBody添加到我的半圆中。我怎么能加一个呢？ （我现在有一个随机的圈子只是为了测试它）

以下是使用的代码：

semiCircle.path = UIBezierPath(arcCenter: CGPoint(x: 0, y: 0), radius: 100, startAngle: CGFloat(Double.pi / 2), endAngle: CGFloat(-Double.pi / 2), clockwise: false).cgPath
semiCircle.position = CGPoint(x: self.frame.width / 2, y: self.frame.height / 2)
semiCircle.physicsBody = SKPhysicsBody(circleOfRadius: CGFloat(300));
semiCircle.physicsBody?.affectedByGravity = false
semiCircle.physicsBody?.isDynamic = false
semiCircle.isHidden = false
semiCircle.strokeColor = SKColor.blue
semiCircle.strokeColor = UIColor.white
semiCircle.lineWidth = 20
semiCircle.name = "ball"
semiCircle.zPosition = 0
addChild(semiCircle)