SCNNode big image on background cause crash

Question

I'm trying to create ruler application with ARKit and SceneKit. I've decided to create ruler image programmatically depends on measured distance.

Here is an extension that I use to draw ruler:

extension UIImage {

    static let dashLineWidth: CGFloat = 2.0
    static let dashDistance: CGFloat = 163.0 / 25.4
    static let rulerFont: UIFont = .systemFont(ofSize: 15.0, weight: .regular)
    static let attributes: [NSAttributedStringKey: Any] = [
        NSAttributedStringKey.font: rulerFont,
        NSAttributedStringKey.foregroundColor: UIColor.black
    ]

    static func drawRuler(width: CGFloat) -> UIImage? {
        let cm = width * 100 // width in centimeters
        let size = CGSize(width: dashDistance * cm * 10, height: 50.0)

        UIGraphicsBeginImageContextWithOptions(size, false, 0.0)
        guard let context = UIGraphicsGetCurrentContext() else { return nil }

        let background = UIBezierPath(rect: CGRect(origin: .zero, size: size))
        context.addPath(background.cgPath)
        context.setFillColor(UIColor.white.cgColor)
        context.fillPath()

        var i: CGFloat = 0.0
        var counter: Int = 0
        while i < size.width {
            let isLongDash = counter % 10 == 0
            let isPartDash = counter % 5 == 0
            let dashHeight: CGFloat = size.height * (isLongDash ? 0.25 : isPartDash ? 0.15 : 0.07)
            UIColor.black.setFill()
            UIRectFill(CGRect(x: i - dashLineWidth / 2, y: 0.0, width: dashLineWidth, height: dashHeight))

            if isLongDash && counter != 0 {
                let value = "\(counter / 10)"
                let valueSize: CGSize = value.size(withAttributes: attributes)
                value.draw(at: CGPoint(x: i - dashLineWidth / 2 - valueSize.width / 2, y: dashHeight + 5.0), withAttributes: attributes)
            }

            i += dashDistance
            counter += 1
        }

        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return image
    }

    func crop(to width: CGFloat, initialWidth: CGFloat) -> UIImage? {
        let rect = CGRect(x: 0, y: 0, width: (width / initialWidth) * size.width * scale, height: size.height * scale)
        guard let croppedCGImage: CGImage = cgImage?.cropping(to: rect) else { return nil }
        return UIImage(cgImage: croppedCGImage)
    }
}

So at first I'm drawing 0.5 meter image only once for better performance and then every time just cropping needed part to display in SCNNode.

And here what I'm trying in my SCNNode class:

var ruler: SCNNode = initRuler()
var initialWidth: CGFloat = 0.5
var rulerImage: UIImage? = UIImage.drawRuler(width: initialWidth)

func updateRuler() {
    guard let geometry = ruler.geometry as? SCNBox else {
        fatalError("Geometry is not SCNBox")
    }
    let width = geometry.width // in meters
    if width > initialWidth - 0.05 {
        initialWidth += 0.5
        rulerImage = UIImage.drawRuler(width: initialWidth)
    }
    guard let croppedImage = rulerImage?.crop(to: width, initialWidth: initialWidth) else { return }
    let texture = SKTexture(image: croppedImage)
    let material = SCNMaterial()
    material.diffuse.contents = texture
    geometry.materials = [material]
}

Everything works fine to the moment when the size of SCNNode becomes bigger and the image is bigger too. So around 1.3 meters I've got a crash

validateTextureDimensions:759: failed assertion `MTLTextureDescriptor has width (16501) greater than the maximum allowed size of 16384.'

Any help would be appreciated. I was thinking if I can split an image in parts and then assign in to material. Or is there an another way to do this?

Answer 1

Instead of setting a single 16501px wide image to one SCNode representing the whole ruler, it makes much more sense to build up your ruler of hundreds of 1cm segments, each with a texture that you draw programmatically for a ruler segment with a number.