背景上的 SCNNode 大图像导致崩溃

Question

我正在尝试使用 ARKit 和 SceneKit 创建标尺应用程序。我决定根据测量的距离以编程方式创建标尺图像。

这是我用来绘制标尺的扩展：

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)
    }
}

所以一开始我只绘制一次 0.5 米的图像以获得更好的性能，然后每次只裁剪需要的部分以在 SCNNode 中显示。

这是我在 SCNNode class 中尝试的内容：

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]
}

当 SCNNode 的大小变大并且图像也变大时，一切正常。所以大约1.3米我撞车了

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

如有任何帮助，我们将不胜感激。我在想是否可以将图像分成几部分，然后分配给 material。或者还有其他方法吗？

Answer 1

首先，最好的办法可能是从互联网上找到标尺的图像或使用 photoshop 之类的工具来制作您自己的标尺，因为以编程方式制作它并不是很快。该错误与称为 MTLTextureDescriptor 的东西有关，问题是您使用的数字太大，这可能是因为您运行使用的设备太小，无法容纳整张照片。

Answer 2

与其将单个 16501px 宽图像设置为一个 SCNode 代表整个标尺，不如将标尺构建成数百个 1cm 段，每个段使用您以编程方式为带有数字的标尺段绘制的纹理。

背景上的 SCNNode 大图像导致崩溃

SCNNode big image on background cause crash

textures

ios

scenekit

swift