如何通过在屏幕上拖动手指来更改相机位置 - Swift

Question

I'm trying to learn ARKIT and make a small demo app to draw in 3D. The following is the code I wrote and so far there are no problems:

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()

    override func viewDidLoad() {
        super.viewDidLoad()

        self.sceneView.session.run(config)
        self.sceneView.delegate = self
    }

    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)
        let cameraCurrentPosition = 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
                }
        }
    }
}

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

As you can see, I set the scene and configure it, I create a button to draw when pressed, a pointer (or viewfinder) that takes the center of the scene and a button to delete the nodes inserted.

Now I would like to be able to move the cameraCurrentPosition to a different point from the center: I would like to move it if possible with a touch on the screen taking the position of the finger. If possible, could someone help me with the code?

Answer 1

Generally speaking, you can't programmatically move the Camera within an ARSCN, the camera transform is the physical position of the device relative to the virtual scene.

With that being said, one way you could draw the user touches to the screen is using the touchesMoved method within your View Controller.

var touchRoots: [SCNNode] = [] // list of root nodes for each set of touches drawn

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    // get the initial touch event
    if let touch = touches.first {
        guard let pointOfView = self.sceneView.pointOfView else { return }
        let transform = pointOfView.transform // transformation matrix
        let orientation = SCNVector3(-transform.m31, -transform.m32, -transform.m33) // camera rotation
        let location = SCNVector3(transform.m41, transform.m42, transform.m43) // location of camera frustum
        let currentPostionOfCamera = orientation + location // center of frustum in world space
        DispatchQueue.main.async {
            let touchRootNode : SCNNode = SCNNode() // create an empty node to serve as our root for the incoming points
            touchRootNode.position = currentPostionOfCamera // place the root node ad the center of the camera's frustum
            touchRootNode.scale = SCNVector3(1.25, 1.25, 1.25)// touches projected in Z will appear smaller than expected - increase scale of root node to compensate
            guard let sceneView = self.sceneView else { return }
            sceneView.scene.rootNode.addChildNode(touchRootNode) // add the root node to the scene
            let constraint = SCNLookAtConstraint(target: self.sceneView.pointOfView) // force root node to always face the camera
            constraint.isGimbalLockEnabled = true // enable gimbal locking to avoid issues with rotations from LookAtConstraint
            touchRootNode.constraints = [constraint] // apply LookAtConstraint

            self.touchRoots.append(touchRootNode)
        }
    }
}

override func func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
    if let touch = touches.first {
        let translation = touch.location(in: self.view)
        let translationFromCenter = CGPoint(x: translation.x - (0.5 * self.view.frame.width), y: translation.y - (0.5 * self.view.frame.height))

        // add nodes using the main thread
        DispatchQueue.main.async {
            guard let touchRootNode = self.touchRoots.last else { return }
            let sphereNode : SCNNode = SCNNode(geometry: SCNSphere(radius: 0.015))
            sphereNode.position = SCNVector3(-1*Float(translationFromCenter.x/1000), -1*Float(translationFromCenter.y/1000), 0)
            sphereNode.geometry?.firstMaterial?.diffuse.contents = UIColor.white
            touchRootNode.addChildNode(sphereNode)  // add point to the active root
        }
    }
}

Note: solution only handles a single touch, but it is simple enough to extend the example to add multi-touch support.