SceneKit - SCNText centering incorrectly

I have tried to make a text string (SCNText) fit inside a box (SCNBox) in the code below. The size of the box looks correct but the text is not in the right center of the box. Any idea or solution? Thanks

let geoText = SCNText(string: "Hello", extrusionDepth: 1.0)
geoText.font = UIFont (name: "Arial", size: 8)
geoText.firstMaterial!.diffuse.contents = UIColor.red
let textNode = SCNNode(geometry: geoText)

let (minVec, maxVec) = textNode.boundingBox
scnScene.rootNode.addChildNode(textNode)

let w = CGFloat(maxVec.x - minVec.x)
let h = CGFloat(maxVec.y - minVec.y)
let d = CGFloat(maxVec.z - minVec.z)

let geoBox = SCNBox(width: w, height: h, length: d, chamferRadius: 0)
geoBox.firstMaterial!.diffuse.contents = UIColor.green.withAlphaComponent(0.5)
scnScene.rootNode.addChildNode(boxNode)

Edited: I have added a new image of the string only (no SCNBox node) with debugOptions showBoundingBoxes to see its bounding box

Solution 1:

From vdugnist's answer, I create a playground code for anyone who wants to test:

import UIKit
import SceneKit
import PlaygroundSupport

var sceneView = SCNView(frame: CGRect(x: 0, y: 0, width: 600, height: 600))
var scene = SCNScene()
sceneView.scene = scene
PlaygroundPage.current.liveView = sceneView

let geoText = SCNText(string: "Hello", extrusionDepth: 1.0)
geoText.font = UIFont (name: "Arial", size: 12)
geoText.firstMaterial!.diffuse.contents = UIColor.red
let textNode = SCNNode(geometry: geoText)

let (minVec, maxVec) = textNode.boundingBox
textNode.position = SCNVector3(x: (minVec.x - maxVec.x) / 2, y: minVec.y - maxVec.y, z: 0)
textNode.pivot = SCNMatrix4MakeTranslation((maxVec.x - minVec.x) / 2, 0, 0)
scene.rootNode.addChildNode(textNode)

let w = CGFloat(maxVec.x - minVec.x)
let h = CGFloat(maxVec.y - minVec.y)
let d = CGFloat(maxVec.z - minVec.z)

let geoBox = SCNBox(width: w, height: h, length: d, chamferRadius: 0)
geoBox.firstMaterial!.diffuse.contents =   UIColor.green.withAlphaComponent(0.5)
let boxNode = SCNNode(geometry: geoBox)
boxNode.position = SCNVector3Make((maxVec.x - minVec.x) / 2 + minVec.x, (maxVec.y - minVec.y) / 2 + minVec.y, 0);
textNode.addChildNode(boxNode)

Solution 2:

I need to move the text to position zero (0, 0, 0) instead of moving both text and the around box, thus I continue to change the pivot of the text from Solution 1. Now the code is as the following:

import UIKit
import SceneKit
import PlaygroundSupport


var sceneView = SCNView(frame: CGRect(x: 0, y: 0, width: 600, height: 600))
var scene = SCNScene()
sceneView.scene = scene
PlaygroundPage.current.liveView = sceneView


let geoText = SCNText(string: "Hello", extrusionDepth: 1.0)
geoText.font = UIFont (name: "Arial", size: 12)
geoText.firstMaterial!.diffuse.contents = UIColor.red
let textNode = SCNNode(geometry: geoText)

let (minVec, maxVec) = textNode.boundingBox
textNode.pivot = SCNMatrix4MakeTranslation((maxVec.x - minVec.x) / 2 + minVec.x, (maxVec.y - minVec.y) / 2 + minVec.y, 0)
scene.rootNode.addChildNode(textNode)

let w = CGFloat(maxVec.x - minVec.x)
let h = CGFloat(maxVec.y - minVec.y)
let d = CGFloat(maxVec.z - minVec.z)

let geoBox = SCNBox(width: w, height: h, length: d, chamferRadius: 0)
geoBox.firstMaterial!.diffuse.contents = UIColor.green.withAlphaComponent(0.6)
let boxNode = SCNNode(geometry: geoBox)
scene.rootNode.addChildNode(boxNode)