Set lineWidth of UIBezierPath for use in SceneKit

Question

I can't get UIBezierPath's lineWidth property to work when using it in SceneKit. The end product has the minimum lineWidth (it's very thin), whereas I need a thick line.

The path is used to construct an SCNShape, which is then used to construct an SCNNode.

Consider the following code:

let hugePath = UIBezierPath()
        
hugePath.lineWidth = 40.0 //Has no effect

hugePath.move(to: CGPoint(x: previousPathPosition.x, y: previousPathPosition.y))

hugePath.addLine(to: CGPoint(x: block.position.x, y: block.position.y))

let hugeShape = SCNShape(path: hugePath, extrusionDepth: 150.0)
let hugeMaterial = SCNMaterial()
hugeMaterial.diffuse.contents = UIColor.red
hugeShape.materials = [hugeMaterial, hugeMaterial, hugeMaterial, hugeMaterial, hugeMaterial, hugeMaterial]

let hugeNode = SCNNode(geometry: hugeShape)
hugeNode.position.x = 0.0 
hugeNode.position.z = 5.0
hugeNode.position.y = 0.0

scnView.scene?.rootNode.addChildNode(hugeNode)

There are numerous SO questions on how this problem pertains to UIBezierPath and CAShapeLayer, but none that I see on how it pertains to SceneKit. With the CAShapeLayer problem, the solution is apparently to set lineWidth on the actual layer -- NOT the path. But that doesn't seem to apply to the SceneKit situation.

How can I create a path for use in SceneKit that has a functioning lineWidth property?

EDIT: What I'm trying to do is connect a series of points with a solid, 3D path. Thanks to Andy's answer, I think I'm on the right track, but I'm still a bit stuck.

So, here's where I'm at now: Instead of trying to create a line by manually drawing each side of a bunch of 2D rectangles that are then extruded (which is what I believe Andy's answer recommends), I'm trying to take advantage of UIBezierPath's apply(_ transform:) method. So, I'm drawing a single line connecting the points (hugePath), then making a copy of that line (hugePathTopPart), then transforming the copy to the desired "lineWidth", then connecting the two lines to form a single path.

Like this:

//Make a copy of the line:
let hugePathTopPart = hugePath.copy() as? UIBezierPath
//Move the copy upward. This is effectively the "lineWidth":
hugePathTopPart?.apply(CGAffineTransform(translationX: 0.0, y: 40.0))
//Combine the lines to (hopefully) create a single object:
hugePath.append(hugePathTopPart!)

The problem, now, is that I have these two parallel lines with a big gap between them. I need to fill that gap so it's just one solid shape/line.

Answer 1

From Apple's docs: "SceneKit uses a right-handed coordinate system where (by default) the direction of view is along the negative z-axis..."

Path geometry starts on the XY plane, and is extruded on the Z-axis.

So, if we start with a (vertical) "line" path and extrude it:

    let path = UIBezierPath()
    path.move(to: .zero)
    path.addLine(to: .init(x: 0.0, y: 1.0))
    
    // extrude it to create the shape
    let shape = SCNShape(path: path, extrusionDepth: 10.0)

We get this:

It has Y and Z dimensions, but no X (width).

So, instead of a line, let's start with a rectangle - 0.1 width and 1.0 height:

    // rectangle bezier path
    let path = UIBezierPath(rect: CGRect(x: 0.0, y: 0.0, width: 0.10, height: 1.0))

We see that the path is on the XY plane... if we extrude it:

    // rectangle bezier path
    let path = UIBezierPath(rect: CGRect(x: 0.0, y: 0.0, width: 0.10, height: 1.0))

    // extrude it to create the shape
    let shape = SCNShape(path: path, extrusionDepth: 10.0)

We get this:

Quick example code:

class WallViewController: UIViewController {
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let sceneView = SCNView(frame: self.view.frame)
        self.view.addSubview(sceneView)
        
        sceneView.allowsCameraControl = true
        sceneView.autoenablesDefaultLighting = true
        sceneView.backgroundColor = .black
        
        let scene = SCNScene()
        sceneView.scene = scene
        
        // rectangle bezier path
        let path = UIBezierPath(rect: CGRect(x: 0.0, y: 0.0, width: 0.10, height: 1.0))
        
        // extrude it to create the shape
        let shape = SCNShape(path: path, extrusionDepth: 10.0)
        
        let mat = SCNMaterial()
        mat.diffuse.contents = UIColor(white: 0.75, alpha: 1.0)
        mat.lightingModel = .physicallyBased
        shape.materials = [mat]
        
        // set shape node
        let shapeNode = SCNNode(geometry: shape)
        
        // add it to the scene
        scene.rootNode.addChildNode(shapeNode)
        
        // let's add a camera for the "starting view"
        let camera = SCNCamera()
        let cameraNode = SCNNode()
        cameraNode.camera = camera
        cameraNode.position = SCNVector3(x: 0.5, y: 2.0, z: 7.0)
        scene.rootNode.addChildNode(cameraNode)
        
        let constraint = SCNLookAtConstraint(target: shapeNode)
        constraint.isGimbalLockEnabled = true
        cameraNode.constraints = [constraint]
        
    }
    
}

---

Edit - based on clarification in comments...

OK, so the goal is to take a UIBezierPath such as this:

and turn it into a SCNNode object like this:

First thing to understand is that drawing a path (such as on a CAShapeLayer) with the layer's .lineWidth = 20 looks like this (the red line is our original path, underneath that we have the same path with strokeColor = lightGray):

However, that line width is drawing only - it doesn't change the geometry of the path.

We can look at copy(strokingWithWidth:lineCap:lineJoin:miterLimit:transform:) (docs) to turn the "outline" into a path:

// create a CGPath by stroking the UIBezierPath
let pathRef = path.cgPath.copy(strokingWithWidth: 20.0, lineCap: CGLineCap.butt, lineJoin: CGLineJoin.miter, miterLimit: 10.0)

Here, the underneath layer has fillColor = lightGray and strokeColor = white:

Looking at the stroke, though, we quickly notice that the geometry is not really the "outline" ... and, if we try to use the resulting path as a SCNode object it will fail.

So we need to "Normalize" the path. If we're using iOS 16+, CGPath has a built-in normalize method. For earlier iOS versions, we'd need to find a suitable substitute:

// create a CGPath by stroking the UIBezierPath
let pathRef = path.cgPath.copy(strokingWithWidth: 20.0, lineCap: CGLineCap.butt, lineJoin: CGLineJoin.miter, miterLimit: 10.0)
    
// convert back to a Normalized UIBezierPath
path = UIBezierPath(cgPath: pathRef.normalized())
    

and now we have a path that looks like this:

Here's some example code to play with. Please note: This is Example Code Only!!! I used a fair bit of hard-coded values to get the desired results - particularly with scaling.

First, a view that let's us draw a path, adding segments with touch-drag. It also displays differently for path-only, lineWidth, stroked and normalized:

enum PathType: Int {
    case path, lineWidth, stroked, normalized
}

class MyPathView: UIView {
    
    // closure to report the path has changed
    public var pathChanged: (([CGPoint]) -> ())?
    
    public var pathType: PathType = .lineWidth {
        didSet {
            shapeLayerA.opacity = 1.0
            shapeLayerA.strokeColor = UIColor.white.cgColor
            shapeLayerB.strokeColor = UIColor.red.cgColor
            switch pathType {
            case .path:
                shapeLayerB.strokeColor = UIColor.white.cgColor
                shapeLayerA.opacity = 0.0
            case .lineWidth:
                shapeLayerA.strokeColor = UIColor.lightGray.cgColor
                shapeLayerA.fillColor = nil
                shapeLayerA.lineWidth = 20
            default:
                shapeLayerA.fillColor = UIColor.lightGray.cgColor
                shapeLayerA.lineWidth = 1
            }
            setNeedsLayout()
        }
    }
    
    private var myPoints: [CGPoint] = []
    private var curTouch: CGPoint = .zero
    
    // shapeLayerA will show either
    //  nothing
    //  path with lineWidth
    //  stroked and filled path from strokingWithWidth
    //  stroked and filled path from Normalized strokingWithWidth
    private let shapeLayerA = CAShapeLayer()
    
    // shapeLayerB will always show the path with lineWidth = 1
    private let shapeLayerB = CAShapeLayer()

    public func reset() {
        myPoints = []
        setNeedsLayout()
    }
    override init(frame: CGRect) {
        super.init(frame: frame)
        commonInit()
    }
    required init?(coder: NSCoder) {
        super.init(coder: coder)
        commonInit()
    }
    private func commonInit() {
        backgroundColor = .black

        layer.addSublayer(shapeLayerA)
        layer.addSublayer(shapeLayerB)

        shapeLayerA.strokeColor = UIColor.white.cgColor
        shapeLayerA.fillColor = nil
        shapeLayerA.lineWidth = 20
        
        shapeLayerB.strokeColor = UIColor.white.cgColor
        shapeLayerB.fillColor = nil
        shapeLayerB.lineWidth = 1
        
        shapeLayerA.opacity = 0.0
    }
    
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        guard let t = touches.first else { return }
        curTouch = t.location(in: self)
        setNeedsLayout()
    }
    override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
        guard let t = touches.first else { return }
        
        // let's keep it inside the view
        var p = t.location(in: self)
        p.x = max(0.0, min(bounds.maxX, p.x))
        p.y = max(0.0, min(bounds.maxY, p.y))
        curTouch = p

        setNeedsLayout()
    }
    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        guard let t = touches.first else { return }
        
        // let's keep it inside the view
        var p = t.location(in: self)
        p.x = max(0.0, min(bounds.maxX, p.x))
        p.y = max(0.0, min(bounds.maxY, p.y))
        myPoints.append(p)

        curTouch = .zero
        
        pathChanged?(myPoints)
        
        setNeedsLayout()
    }
    override func layoutSubviews() {
        super.layoutSubviews()
        
        var path: UIBezierPath!
        
        if myPoints.isEmpty {
            myPoints.append(.init(x: 20.0, y: bounds.midY))
            pathChanged?(myPoints)
        }
        
        path = UIBezierPath()
        
        myPoints.forEach { pt in
            if pt == myPoints.first {
                path.move(to: pt)
            } else {
                path.addLine(to: pt)
            }
        }
        if curTouch != .zero {
            path.addLine(to: curTouch)
        }
        
        shapeLayerB.path = path.cgPath
        
        if pathType != .lineWidth {
            // create a CGPath by stroking the path
            let pathRef = path.cgPath.copy(strokingWithWidth: 20.0, lineCap: CGLineCap.butt, lineJoin: CGLineJoin.miter, miterLimit: 10.0)
            if pathType == .stroked {
                // convert back to a UIBezierPath
                path = UIBezierPath(cgPath: pathRef)
            } else {
                // convert back to a Normalized UIBezierPath
                path = UIBezierPath(cgPath: pathRef.normalized())
            }
        }

        shapeLayerA.path = path.cgPath
        
    }
    
}

Next, a controller to hold the drawing view and a SCNView, as well as a couple options:

class ExampleViewController: UIViewController {

    var pathView: MyPathView!
    
    var sceneView: SCNView!
    var scene: SCNScene!
    
    var cameraNode: SCNNode!
    var shapeNode: SCNNode!
    
    var pathPoints: [CGPoint] = []
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        view.backgroundColor = UIColor(white: 0.95, alpha: 1.0)

        pathView = MyPathView()
        
        sceneView = SCNView(frame: .zero)
        sceneView.allowsCameraControl = true
        sceneView.autoenablesDefaultLighting = true
        sceneView.backgroundColor = .black
        
        scene = SCNScene()
        sceneView.scene = scene

        // a couple options
        let resetButton: UIButton = {
            let v = UIButton()
            v.setTitle("Reset", for: [])
            v.setTitleColor(.white, for: .normal)
            v.setTitleColor(.lightGray, for: .highlighted)
            v.backgroundColor = .systemBlue
            v.layer.cornerRadius = 6
            v.addTarget(self, action: #selector(resetTapped(_:)), for: .touchUpInside)
            return v
        }()
        let segCtrl = UISegmentedControl(items: ["path", "lineWidth", "stroked", "normalized"])
        segCtrl.selectedSegmentIndex = 0
        segCtrl.addTarget(self, action: #selector(segChanged(_:)), for: .valueChanged)
        
        let cStack = UIStackView(arrangedSubviews: [resetButton, segCtrl])
        cStack.spacing = 12
        
        [cStack, pathView, sceneView].forEach { v in
            v.translatesAutoresizingMaskIntoConstraints = false
            view.addSubview(v)
        }

        let g = view.safeAreaLayoutGuide
        NSLayoutConstraint.activate([

            cStack.topAnchor.constraint(equalTo: g.topAnchor, constant: 20.0),
            cStack.leadingAnchor.constraint(equalTo: g.leadingAnchor, constant: 40.0),
            cStack.trailingAnchor.constraint(equalTo: g.trailingAnchor, constant: -40.0),

            resetButton.widthAnchor.constraint(equalToConstant: 160.0),

            pathView.topAnchor.constraint(equalTo: cStack.bottomAnchor, constant: 20.0),
            pathView.leadingAnchor.constraint(equalTo: g.leadingAnchor, constant: 40.0),
            pathView.trailingAnchor.constraint(equalTo: g.trailingAnchor, constant: -40.0),
            pathView.bottomAnchor.constraint(equalTo: sceneView.topAnchor, constant: -40.0),

            sceneView.leadingAnchor.constraint(equalTo: g.leadingAnchor, constant: 0.0),
            sceneView.trailingAnchor.constraint(equalTo: g.trailingAnchor, constant: 0.0),
            sceneView.bottomAnchor.constraint(equalTo: g.bottomAnchor, constant: 0.0),
            sceneView.heightAnchor.constraint(equalTo: g.heightAnchor, multiplier: 0.5),

        ])
        
        pathView.pathChanged = { [weak self] pts in
            guard let self = self else { return }
            self.pathPoints = []
            // let's normalize the path points by
            //  setting minimum X and Y to zero
            // and, because CALayer uses 0,0 at top left we'll also
            //  invert the Y values
            let minx = pts.min(by: {$0.x < $1.x})!
            let miny = pts.min(by: {$0.y < $1.y})!
            pts.forEach { pt in
                self.pathPoints.append(.init(x: pt.x - minx.x, y: -(pt.y - miny.y)))
            }
            self.updateScene()
        }
        
        initScene()
    }
    func initScene() {

        scene = SCNScene()
        sceneView.scene = scene
        
        // add a RGB axis indicator
        let axis = Origin(radiusRatio: 0.02)
        axis.simdScale = simd_float3(x: 200.0, y: 200.0, z: 200.0)
        scene.rootNode.addChildNode(axis)

        // add a camera node
        cameraNode = SCNNode()
        cameraNode.camera = SCNCamera()
        scene.rootNode.addChildNode(cameraNode)

        // position it off-center
        cameraNode.position = SCNVector3Make(10, 20, 50)

        // tell the camera to look at the center of the axis indicator
        let constraint = SCNLookAtConstraint(target: axis)
        constraint.isGimbalLockEnabled = true
        cameraNode.constraints = [constraint]
        
    }
    
    @objc func resetTapped(_ sender: Any?) {
        pathPoints = []
        // remove previously added shape if it exists
        if let sn = shapeNode {
            sn.removeFromParentNode()
        }
        pathView.reset()
    }
    @objc func segChanged(_ sender: UISegmentedControl) {
        if let pt = PathType(rawValue: sender.selectedSegmentIndex) {
            pathView.pathType = pt
        }
    }
    func updateScene() {
        
        if pathPoints.isEmpty {
            // nothing to generate yet
            return()
        }

        // remove previously added shape if it exists
        if let sn = shapeNode {
            sn.removeFromParentNode()
        }
        
        // generate path
        var path = UIBezierPath()
        path.move(to: pathPoints[0])
        for i in 1..<pathPoints.count {
            path.addLine(to: pathPoints[i])
        }

        // create a CGPath by stroking the UIBezierPath
        let pathRef = path.cgPath.copy(strokingWithWidth: 20.0, lineCap: CGLineCap.butt, lineJoin: CGLineJoin.miter, miterLimit: 10.0)
        
        // convert back to a Normalized UIBezierPath
        path = UIBezierPath(cgPath: pathRef.normalized())
        
        // this only has an effect if we have arcs in the path
        path.flatness = 0
        
        // our path is based on points, so
        // scale down by 10
        path.apply(CGAffineTransform(scaleX: 0.1, y: 0.1))

        // extrude it to create the shape
        let shape = SCNShape(path: path, extrusionDepth: 10.0)
        
        let mat = SCNMaterial()
        mat.diffuse.contents = UIColor.systemYellow
        mat.lightingModel = .physicallyBased
        shape.materials = [mat]
        
        // set shape node
        shapeNode = SCNNode(geometry: shape)

        // add it to the scene
        scene.rootNode.addChildNode(shapeNode)

        // move the shape so its boundingBox is centered at 0,0,0
        let box = shapeNode.boundingBox
        let xx = box.max.x - box.min.x
        let yy = box.min.y - box.max.y
        shapeNode.position = SCNVector3(x: -xx * 0.5, y: -yy * 0.5, z: 0.0)
        
    }
    
}

And, a few "helper" classes / extensions used in the above code:

// slightly modified version from
//  https://gist.github.com/cenkbilgen/ba5da0b80f10dc69c10ee59d4ccbbda6
class Origin: SCNNode {
    
    // see: https://developer.apple.com/documentation/arkit/arsessionconfiguration/worldalignment/gravityandheading
    // if ar session configured with gravity and heading, then +x is east, +y is up, +z is south
    
    private enum Axis {
        case x, y, z
        
        //var normal: float3 {
        var normal: SIMD3<Float> {
            switch self {
            case .x: return simd_float3(1, 0, 0)
            case .y: return simd_float3(0, 1, 0)
            case .z: return simd_float3(0, 0, 1)
            }
        }
    }
    
    // TODO: Set pivot to origin and redo tranforms, it'll make it easier to place additional nodes
    
    init(length: CGFloat = 0.1, radiusRatio ratio: CGFloat = 0.04, color: (x: UIColor, y: UIColor, z: UIColor, origin: UIColor) = (.systemRed, .systemGreen, .systemBlue, .cyan)) {
        
        // x-axis
        let xAxis1 = SCNCylinder(radius: length*ratio, height: length)
        xAxis1.firstMaterial?.diffuse.contents = color.x.darker()
        let xAxisNode1 = SCNNode(geometry: xAxis1)
        xAxisNode1.simdWorldOrientation = simd_quatf.init(angle: .pi/2, axis: Axis.z.normal)
        xAxisNode1.simdWorldPosition = simd_float1(length) * 0.5 * Axis.x.normal

        let xAxis2 = SCNCylinder(radius: length*ratio, height: length)
        xAxis2.firstMaterial?.diffuse.contents = color.x.lighter()
        let xAxisNode2 = SCNNode(geometry: xAxis2)
        xAxisNode2.simdWorldOrientation = simd_quatf.init(angle: .pi/2, axis: Axis.z.normal)
        xAxisNode2.simdWorldPosition = simd_float1(length) * -0.5 * Axis.x.normal

        // y-axis
        let yAxis1 = SCNCylinder(radius: length*ratio, height: length)
        yAxis1.firstMaterial?.diffuse.contents = color.y.darker()
        let yAxisNode1 = SCNNode(geometry: yAxis1)
        yAxisNode1.simdWorldPosition = simd_float1(length) * 0.5 * Axis.y.normal // just shift

        // y-axis
        let yAxis2 = SCNCylinder(radius: length*ratio, height: length)
        yAxis2.firstMaterial?.diffuse.contents = color.y.lighter()
        let yAxisNode2 = SCNNode(geometry: yAxis2)
        yAxisNode2.simdWorldPosition = simd_float1(length) * -0.5 * Axis.y.normal // just shift

        // z-axis
        let zAxis1 = SCNCylinder(radius: length*ratio, height: length)
        zAxis1.firstMaterial?.diffuse.contents = color.z.darker()
        let zAxisNode1 = SCNNode(geometry: zAxis1)
        zAxisNode1.simdWorldOrientation = simd_quatf(angle: -.pi/2, axis: Axis.x.normal)
        zAxisNode1.simdWorldPosition = simd_float1(length) * 0.5 * Axis.z.normal
        
        // z-axis
        let zAxis2 = SCNCylinder(radius: length*ratio, height: length)
        zAxis2.firstMaterial?.diffuse.contents = color.z.lighter()
        let zAxisNode2 = SCNNode(geometry: zAxis2)
        zAxisNode2.simdWorldOrientation = simd_quatf(angle: -.pi/2, axis: Axis.x.normal)
        zAxisNode2.simdWorldPosition = simd_float1(length) * -0.5 * Axis.z.normal
        
        // dot at origin
        let origin = SCNSphere(radius: length*ratio)
        origin.firstMaterial?.diffuse.contents = color.origin
        let originNode = SCNNode(geometry: origin)
        
        super.init()
        
        self.addChildNode(originNode)
        self.addChildNode(xAxisNode1)
        self.addChildNode(xAxisNode2)
        self.addChildNode(yAxisNode1)
        self.addChildNode(yAxisNode2)
        self.addChildNode(zAxisNode1)
        self.addChildNode(zAxisNode2)

    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }
    
}

// typical UIColor extension for lighter / darker
extension UIColor {
    
    func lighter(by percentage: CGFloat = 30.0) -> UIColor? {
        return self.adjust(by: abs(percentage) )
    }
    
    func darker(by percentage: CGFloat = 30.0) -> UIColor? {
        return self.adjust(by: -1 * abs(percentage) )
    }
    
    func adjust(by percentage: CGFloat = 30.0) -> UIColor? {
        var red: CGFloat = 0, green: CGFloat = 0, blue: CGFloat = 0, alpha: CGFloat = 0
        if self.getRed(&red, green: &green, blue: &blue, alpha: &alpha) {
            return UIColor(red: min(red + percentage/100, 1.0),
                           green: min(green + percentage/100, 1.0),
                           blue: min(blue + percentage/100, 1.0),
                           alpha: alpha)
        } else {
            return nil
        }
    }
    
}

Running that example code gives us this to play with:

Again, Example Code Only!!! - and will work best on an iPad.

Answer 2

SCNScene visualizes only 3D renderable surfaces. So, since an object of UIBezierPath isn't a renderable surface (it's just a 2D line), its own width has no effect in SceneKit's 3D scene.

You need to extrude a 3D line. Here's the solution:

override func viewDidLoad() {
    super.viewDidLoad()
    
    let sceneView = self.view as! SCNView
    sceneView.scene = SCNScene()
    sceneView.allowsCameraControl = true
    sceneView.backgroundColor = .black
    sceneView.scene?.rootNode.addChildNode(createLine(0.03, length: 10.0))
}

func createLine(_ lineWidth: Double, length: Double) -> SCNNode {
            
    let path = UIBezierPath()
    path.move(to: CGPoint(x: length, y: 0))
    path.addLine(to: CGPoint(x: length, y: lineWidth))
    path.addLine(to: CGPoint(x: 0, y: lineWidth))
    path.addLine(to: CGPoint(x: 0, y: 0))
    path.close()
    
    let shape = SCNShape(path: path, extrusionDepth: lineWidth)
    let material = SCNMaterial()
    material.lightingModel = .constant
    material.diffuse.contents = UIColor.systemRed
    shape.materials = [material]
    
    let lineNode = SCNNode(geometry: shape)
    return lineNode
}