基于ARKit的AR尺子Demo代码分析

final class ViewController: UIViewController {
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        resetValues()
        isMeasuring = true
        targetImageView.image = UIImage(named: "targetGreen")
    }
  
    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        isMeasuring = false
        targetImageView.image = UIImage(named: "targetWhite")
        if let line = currentLine {
            lines.append(line)
            currentLine = nil
            resetButton.isHidden = false
            resetImageView.isHidden = false
        }
    }
}

extension ViewController: ARSCNViewDelegate {
    func renderer(_ renderer: SCNSceneRenderer, updateAtTime time: TimeInterval) {
        DispatchQueue.main.async { [weak self] in
            self?.detectObjects()
        }
    }
}
  
extension ViewController {
    fileprivate func detectObjects() {
        guard let worldPosition =
          sceneView.realWorldVector(screenPosition: view.center) else { return }
        targetImageView.isHidden = false
        meterImageView.isHidden = false
        if lines.isEmpty {
            messageLabel.text = "Hold screen & move your phone…"
        }
        loadingView.stopAnimating()
        if isMeasuring {
            if startValue == vectorZero {
                startValue = worldPosition
                currentLine = Line(sceneView: sceneView, startVector: startValue, unit: unit)
            }
            endValue = worldPosition
            currentLine?.update(to: endValue)
            messageLabel.text = currentLine?.distance(to: endValue) ?? "Calculating…"
        }
    }
}
  
extension ARSCNView {
    func realWorldVector(screenPosition: CGPoint) -> SCNVector3? {
        let results = self.hitTest(screenPosition, types: [.featurePoint])
        guard let result = results.first else { return nil }
        return SCNVector3.positionFromTransform(result.worldTransform)
    }
}
  
final class Line {
    func distance(to vector: SCNVector3) -> String {
        return String(format: "%.2f%@", startVector.distance(from: vector) * unit.fator, unit.unit)
    }
}