在swift SceneKit中使用顶点绘制自定义节点的示例是什么？

This area is hardly documented online and it would be great to see a working Swift 3 example, of say, a custom drawn cube with manual SCNvector3s. There is this in objective-C but not Swift. This might not be a usual form of question but I know it would help many. If there is somewhere I missed, please mention.This area is hardly documented online and it wo