Extracting vertices from scenekit

Question

I\'m having a problem with understanding scenekit geometery.

I have the default cube from Blender, and I export as collada (DAE), and can bring it into scenekit....

Answer 1

// call this function _ = vertices(node: mySceneView.scene!.rootNode) // I have get the volume in Swift 4.2 :--- this function

func vertices(node:SCNNode) -> [SCNVector3] {

    let planeSources1 = node.childNodes.first?.geometry

    let planeSources = planeSources1?.sources(for: SCNGeometrySource.Semantic.vertex)
    if let planeSource = planeSources?.first {

        let stride = planeSource.dataStride
        let offset = planeSource.dataOffset
        let componentsPerVector = planeSource.componentsPerVector
        let bytesPerVector = componentsPerVector * planeSource.bytesPerComponent

        let vectors = [SCNVector3](repeating: SCNVector3Zero, count: planeSource.vectorCount)
        let vertices = vectors.enumerated().map({
            (index: Int, element: SCNVector3) -> SCNVector3 in
            let vectorData = UnsafeMutablePointer<Float>.allocate(capacity: componentsPerVector)
            let nsByteRange = NSMakeRange(index * stride + offset, bytesPerVector)
            let byteRange = Range(nsByteRange)

            let buffer = UnsafeMutableBufferPointer(start: vectorData, count: componentsPerVector)
            planeSource.data.copyBytes(to: buffer, from: byteRange)
            return SCNVector3Make(buffer[0], buffer[1], buffer[2])
        })
        var totalVolume = Float()
        var x1 = Float(),x2 = Float(),x3 = Float(),y1 = Float(),y2 = Float(),y3 = Float(),z1 = Float(),z2 = Float(),z3 = Float()
        var i = 0
        while i < vertices.count{

                x1 = vertices[i].x;
                y1 = vertices[i].y;
                z1 = vertices[i].z;

                x2 = vertices[i + 1].x;
                y2 = vertices[i + 1].y;
                z2 = vertices[i + 1].z;

                x3 = vertices[i + 2].x;
                y3 = vertices[i + 2].y;
                z3 = vertices[i + 2].z;

                totalVolume +=
                    (-x3 * y2 * z1 +
                        x2 * y3 * z1 +
                        x3 * y1 * z2 -
                        x1 * y3 * z2 -
                        x2 * y1 * z3 +
                        x1 * y2 * z3);

                        i = i + 3
        }
        totalVolume = totalVolume / 6;
        volume = "\(totalVolume)"
        print("Volume Volume Volume Volume Volume Volume Volume :\(totalVolume)")
        lbl_valume.text = "\(clean(String(totalVolume))) cubic mm"
    }
    return[]
}