如何使SceneKit SCNCameraController的frameNodes正确设置目标？

我也遇到过这个问题，确实frameNodes(_:)在iOS 11.x版本处理多节点时存在明确的bug——它只会调整相机视角让所有节点进入视野，但完全不会按照头文件注释所说的，将相机目标设置为所有节点包围球的中心，默认会 fallback 到原点(0,0,0)。下面是我验证过的解决思路和代码：

简便计算多节点包围体中心的方法 #

要手动获取多个节点的整体包围体中心，你可以遍历所有节点的boundingBox，合并出一个能包含所有节点的最小包围盒，再计算这个包围盒的中心坐标。这个方法轻量且可靠：

func calculateCombinedBoundingBoxCenter(nodes: [SCNNode]) -> SCNVector3 {
    guard !nodes.isEmpty else { return SCNVector3Zero }
    
    // 初始化最小/最大边界为第一个节点的包围盒
    var minVector = nodes[0].boundingBox.min
    var maxVector = nodes[0].boundingBox.max
    
    // 遍历剩余节点，扩展边界以包含所有节点
    for node in nodes.dropFirst() {
        let nodeMin = node.boundingBox.min
        let nodeMax = node.boundingBox.max
        
        minVector.x = min(minVector.x, nodeMin.x)
        minVector.y = min(minVector.y, nodeMin.y)
        minVector.z = min(minVector.z, nodeMin.z)
        
        maxVector.x = max(maxVector.x, nodeMax.x)
        maxVector.y = max(maxVector.y, nodeMax.y)
        maxVector.z = max(maxVector.z, nodeMax.z)
    }
    
    // 返回包围盒中心
    return SCNVector3(
        x: (minVector.x + maxVector.x) / 2,
        y: (minVector.y + maxVector.y) / 2,
        z: (minVector.z + maxVector.z) / 2
    )
}

修复后的Playground代码 #

把这个计算方法整合到你的示例代码中，手动设置相机控制器的target，就能解决旋转目标错误的问题：

import UIKit
import SceneKit
import PlaygroundSupport

var sceneView = SCNView(frame: CGRect(x: 0, y: 0, width: 400, height: 400))
var scene = SCNScene()
sceneView.scene = scene
PlaygroundPage.current.liveView = sceneView
sceneView.autoenablesDefaultLighting = true

var cameraNode = SCNNode()
cameraNode.camera = SCNCamera()
cameraNode.position = SCNVector3(x: 0, y: 0, z: 10)
scene.rootNode.addChildNode(cameraNode)

sceneView.allowsCameraControl = true
sceneView.defaultCameraController.interactionMode = .orbitTurntable
sceneView.defaultCameraController.pointOfView = sceneView.pointOfView

var torus = SCNTorus(ringRadius: 1, pipeRadius: 0.5)
var torusNode = SCNNode(geometry: torus)
torusNode.position = SCNVector3(0, 0, 0)
scene.rootNode.addChildNode(torusNode)
torus.firstMaterial?.diffuse.contents = UIColor.red
torus.firstMaterial?.specular.contents = UIColor.white

var cube = SCNBox(width: 1, height: 1, length: 1, chamferRadius: 0)
var cubeNode = SCNNode(geometry: cube)
cubeNode.position = SCNVector3(4, 0, 0)
scene.rootNode.addChildNode(cubeNode)
cube.firstMaterial?.diffuse.contents = UIColor.blue
cube.firstMaterial?.specular.contents = UIColor.white

// 计算多节点的包围盒中心
let targetCenter = calculateCombinedBoundingBoxCenter(nodes: [torusNode, cubeNode])

SCNTransaction.begin()
SCNTransaction.animationDuration = 1.0
sceneView.defaultCameraController.frameNodes([torusNode, cubeNode])
// 手动设置正确的旋转目标
sceneView.defaultCameraController.target = targetCenter
SCNTransaction.commit()

// 新增的包围盒计算函数
func calculateCombinedBoundingBoxCenter(nodes: [SCNNode]) -> SCNVector3 {
    guard !nodes.isEmpty else { return SCNVector3Zero }
    
    var minVector = nodes[0].boundingBox.min
    var maxVector = nodes[0].boundingBox.max
    
    for node in nodes.dropFirst() {
        let nodeMin = node.boundingBox.min
        let nodeMax = node.boundingBox.max
        
        minVector.x = min(minVector.x, nodeMin.x)
        minVector.y = min(minVector.y, nodeMin.y)
        minVector.z = min(minVector.z, nodeMin.z)
        
        maxVector.x = max(maxVector.x, nodeMax.x)
        maxVector.y = max(maxVector.y, nodeMax.y)
        maxVector.z = max(maxVector.z, nodeMax.z)
    }
    
    return SCNVector3(
        x: (minVector.x + maxVector.x) / 2,
        y: (minVector.y + maxVector.y) / 2,
        z: (minVector.z + maxVector.z) / 2
    )
}

修改后，相机会正确围绕圆环和立方体之间的中心旋转，这个方法在iOS 11.2.1及后续测试过的版本中都能稳定工作，直到苹果修复frameNodes的底层bug。

内容的提问来源于stack exchange，提问作者LenK