Swift中如何通过手指拖动调整ARKit相机位置（3D绘图Demo）

Great work on your ARKit 3D drawing demo! To make the drawing position follow where the user touches the screen, we need to convert 2D touch coordinates into a 3D world position using ARKit's hit-testing capabilities. Here's a step-by-step modification to your code:

Key Changes Explained #

1. Track Touch Position: Add a variable to store the 3D world position corresponding to the user's touch.
2. Convert Touch to 3D Space: Use hitTest to map the screen touch to a real-world position (either on a detected plane or a point in front of the camera if no plane is found).
3. Update Drawing Logic: Modify your renderer method to use the touch-derived position instead of the camera's center when the user is touching the screen.

Modified Full Code #

import UIKit
import ARKit

class ViewController: UIViewController, ARSCNViewDelegate {
    @IBOutlet weak var sceneView: ARSCNView!
    @IBOutlet weak var DRAW: UIButton!
    @IBOutlet weak var DEL: UIButton!
    let config = ARWorldTrackingConfiguration()
    // Variable to store the 3D position from user touch
    private var touchWorldPosition: SCNVector3?
    
    override func viewDidLoad() {
        super.viewDidLoad()
        self.sceneView.session.run(config)
        self.sceneView.delegate = self
        // Enable horizontal plane detection for more accurate hit test results
        config.planeDetection = .horizontal
    }
    
    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        guard let touch = touches.first else { return }
        let touchLocation = touch.location(in: sceneView)
        
        // Perform hit test to find real-world position matching the touch
        let hitTestResults = sceneView.hitTest(touchLocation, types: [.existingPlaneUsingExtent, .estimatedHorizontalPlane])
        
        if let result = hitTestResults.first {
            // Extract world position from the hit test result's transform
            let worldTransform = result.worldTransform
            touchWorldPosition = SCNVector3(
                worldTransform.columns.3.x,
                worldTransform.columns.3.y,
                worldTransform.columns.3.z
            )
        } else {
            // Fallback: if no plane is detected, use a point 0.5 meters in front of the camera
            guard let pointOfView = sceneView.pointOfView else { return }
            let transform = pointOfView.transform
            let cameraOrientation = SCNVector3(-transform.m31, -transform.m32, -transform.m33)
            let cameraLocation = SCNVector3(transform.m41, transform.m42, transform.m43)
            touchWorldPosition = cameraLocation + cameraOrientation * 0.5
        }
    }
    
    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        // Reset touch position when the user stops touching the screen
        touchWorldPosition = nil
    }
    
    func renderer(_ renderer: SCNSceneRenderer, willRenderScene scene: SCNScene, atTime time: TimeInterval) {
        guard let pointOfView = sceneView.pointOfView else {return}
        let transform = pointOfView.transform
        let cameraOrientation = SCNVector3(-transform.m31,-transform.m32,-transform.m33)
        let cameraLocation = SCNVector3(transform.m41,transform.m42,transform.m43)
        // Use touch-derived position if available; fall back to camera center otherwise
        let cameraCurrentPosition = touchWorldPosition ?? (cameraOrientation + cameraLocation)
        
        DispatchQueue.main.async {
            if (self.DRAW.isTouchInside){
                let sphereNode = SCNNode(geometry: SCNSphere(radius: 0.02))
                sphereNode.position = cameraCurrentPosition
                self.sceneView.scene.rootNode.addChildNode(sphereNode)
                sphereNode.geometry?.firstMaterial?.diffuse.contents = UIColor.red
                print("RED Button is Pressed")
            }else if (self.DEL.isTouchInside){
                self.sceneView.scene.rootNode.enumerateChildNodes{ (node, stop) in
                    node.removeFromParentNode()
                }
            }else{
                let pointer = SCNNode(geometry: SCNSphere(radius: 0.01))
                pointer.name = "pointer"
                pointer.position = cameraCurrentPosition
                self.sceneView.scene.rootNode.enumerateChildNodes({(node,_) in
                    if node.name == "pointer"{
                        node.removeFromParentNode()
                    }
                })
                self.sceneView.scene.rootNode.addChildNode(pointer)
                pointer.geometry?.firstMaterial?.diffuse.contents = UIColor.purple
            }
        }
    }
}

// Helper operators for vector math
func +(left:SCNVector3,right:SCNVector3) -> SCNVector3 {
    return SCNVector3Make(left.x + right.x, left.y + right.y, left.z + right.z)
}

func *(left: SCNVector3, right: Float) -> SCNVector3 {
    return SCNVector3Make(left.x * right, left.y * right, left.z * right)
}

Additional Notes #

• Plane Detection: I enabled horizontal plane detection in viewDidLoad to make hit tests more accurate when the user touches flat surfaces like tables or floors.
• Fallback Distance: The fallback position uses a point 0.5 meters in front of the camera—you can adjust this distance by changing the 0.5 value in the fallback logic.
• Continuous Touch Updates: touchesMoved updates the 3D position in real-time as the user drags their finger, and touchesEnded resets the position when they lift their finger.

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