let positions = unsafeBitCast(positionsIn!.contents(), to: UnsafeMutablePointer<Float>.self)
    let _velocities = unsafeBitCast(velocities!.contents(), to: UnsafeMutablePointer<Float>.self)

这个是报错的位置，提示的错误信息如下：
Thread 1: Fatal error: Unexpectedly found nil while unwrapping an Optional value
不太熟悉swift、metal，能告诉这个是什么问题吗？

What are the ways to generate data formats in a project?

Thank you for this project. It has tought me a lot. It runs smoothly with the object count that it currently has, but when increasing the amount of points to render by just a little (4x for example) everything starts lagging a lot, including the rest of the MacOS of a maxed out MBP.
Any help is appreciated!