Swift SceneKit中concavePolyhedron下contactTest检测失效问题求助

我开发的拖拽游戏里，释放手指时需要检测物体重叠，用SCNPhysicsWorld.contactTest(with:)方法，当物理体用.convexHull时正常，但改成.concavePolyhedron后完全没接触结果返回，物理体已经设为static。

配置物理体的代码：

parentNode.physicsBody = SCNPhysicsBody(type: .static, shape: SCNPhysicsShape(node: parentNode, options: [.type: SCNPhysicsShape.ShapeType.concavePolyhedron, .collisionMargin: 0.0, .scale: scaleVector]))

调用检测的代码：

if let test = currentNode?.physicsBody {
     let list = view.scene!.physicsWorld.contactTest(with: test) {
          ...
     }
}

原因分析 #

SceneKit的物理引擎对凹面体（concavePolyhedron）的碰撞检测有特殊限制：

• 凹面体设计初衷是作为静态环境障碍物（比如地形、墙壁），引擎不会主动计算两个静态凹面体之间的接触，因为这类场景在物理模拟中被视为固定不动的，不会产生动态交互。
• contactTest(with:)方法对凹面体的支持有限，仅能检测动态物体（.dynamic类型）与静态凹面体的碰撞，无法处理两个静态凹面体或静态凹面体作为主动检测对象的情况。

解决方案 #

方案1：临时切换物理形状做检测 #

拖动结束时，把被拖动物体的物理形状临时替换为.convexHull完成检测，之后再切回.concavePolyhedron：

@objc
func handlePan(_ sender: UIPanGestureRecognizer) {
    // ... 其他拖拽逻辑 ...
    
    if sender.state == .ended {
        guard let currentNode = currentNode, let originalShape = currentNode.physicsBody?.shape else { return }
        
        // 临时替换为convexHull
        let tempShape = SCNPhysicsShape(node: currentNode, options: [.type: SCNPhysicsShape.ShapeType.convexHull, .collisionMargin: 0.0])
        currentNode.physicsBody?.shape = tempShape
        
        // 执行接触检测
        if let test = currentNode.physicsBody {
            let list = scnView?.scene?.physicsWorld.contactTest(with: test)
            if list?.count ?? 0 > 0 {
                currentNode.position = beginningPos ?? currentNode.position
            }
        }
        
        // 切回原concavePolyhedron形状
        currentNode.physicsBody?.shape = originalShape
    }
}

方案2：添加凸面体碰撞代理 #

给凹面体节点额外配置一个凸面体物理形状作为碰撞检测的代理，保持视觉显示为凹面，但碰撞检测用凸包：

// 配置节点时
let node1 = SCNNode(geometry: SCNBox(width: 1, height: 1, length: 1, chamferRadius: 0))
node1.position = SCNVector3(x: 0, y: 0, z: 0)
// 视觉用原节点，碰撞检测用convexHull的物理体
node1.physicsBody = SCNPhysicsBody(type: .static, shape: SCNPhysicsShape(node: node1, options: [.type: SCNPhysicsShape.ShapeType.convexHull, .collisionMargin: 0.0]))
scene.rootNode.addChildNode(node1)

如果必须保留凹面体的物理特性，可以给节点添加一个隐藏的子节点，用凸面体做碰撞检测，原节点的凹面体仅用于渲染。

方案3：手动几何检测 #

如果需要精确的凹面体重叠检测，可以手动实现基于 bounding box 或射线的检测逻辑：

// 示例：检测两个节点的bounding box是否重叠
func isNodeOverlapping(_ nodeA: SCNNode, _ nodeB: SCNNode) -> Bool {
    let boxA = nodeA.boundingBox
    let boxB = nodeB.boundingBox
    
    // 转换为世界坐标系下的边界
    let minA = nodeA.convertPosition(boxA.min, to: nil)
    let maxA = nodeA.convertPosition(boxA.max, to: nil)
    let minB = nodeB.convertPosition(boxB.min, to: nil)
    let maxB = nodeB.convertPosition(boxB.max, to: nil)
    
    // 检测轴对齐包围盒是否重叠
    let xOverlap = maxA.x >= minB.x && maxB.x >= minA.x
    let yOverlap = maxA.y >= minB.y && maxB.y >= minA.y
    let zOverlap = maxA.z >= minB.z && maxB.z >= minA.z
    
    return xOverlap && yOverlap && zOverlap
}

// 在拖动结束时调用
if sender.state == .ended {
    guard let currentNode = currentNode else { return }
    let sceneNodes = scnView?.scene?.rootNode.childNodes.filter { $0 != currentNode }
    let hasOverlap = sceneNodes?.contains { isNodeOverlapping(currentNode, $0) } ?? false
    if hasOverlap {
        currentNode.position = beginningPos ?? currentNode.position
    }
}

内容的提问来源于stack exchange，提问作者justinzh0905