ARKit SCNVector3 和扩展不能一起工作

问题描述

我有一个应用程序，旨在记录相机当前的 X、Y、Z 坐标并将它们打印出来.它使用下面的代码正确地做到了这一点

I have an app that that aims to record the camera's current X,Y,Z coordinates and print them out. It does this properly with the code down below

func renderer(_ renderer: SCNSceneRenderer, willRenderScene scene: SCNScene, atTime time: TimeInterval) {

        guard let pointOfView = sceneView.pointOfView else { return }
        let transform = pointOfView.transform
        let CamPosition = SCNVector3(transform.m41, transform.m42, transform.m43)
        print(CamPosition)

我想截断打印的输出，因为它很长.我发现这个扩展可以截断值.

I want to truncate the printed output since it's very long. I found this extension to truncate the values.

extension Double {
    func truncate(places : Int)-> Double {
        return Double(floor(pow(10.0, Double(places)) * self)/pow(10.0, Double(places)))
    }
}

如果我打印这样的东西，这会起作用:

This works if I print something like this:

x = 1.123456789
print(x.truncate(places: 2))

但如果我像这样打印出来将无法工作:

but will not work if I print it out like this:

print(camRotation.truncate(palces:2))

它给我的错误是'SCNVector4'类型的值没有成员'truncate'"

The error it gives me says "Value of type 'SCNVector4' has no member 'truncate'"

这是我的格式问题还是 SCNVectors 不允许您使用扩展?

is this a formatting issue on my end or do SCNVectors just not allow you to use extensions?

推荐答案

camRotation 是一个 SCNVector4.

您的扩展程序位于 Double，而不是 SCNVector4.

Your extension is on Double, not SCNVector4.

          /// Double, not SCNVector4
extension Double {
    func truncate(places : Int)-> Double {
        return Double(floor(pow(10.0, Double(places)) * self)/pow(10.0, Double(places)))
    }
}

扩展适用于任何类型，但 camRotation.truncate(palces:2) 不起作用，因为类型不匹配.

Extensions work on any type, but camRotation.truncate(palces:2) doesn't work, because the type doesn't match.

好的，现在进入实际答案.目前，您的代码说

Ok, now on to the actual answer. Currently, your code says

let CamPosition = SCNVector3(transform.m41, transform.m42, transform.m43)

只需将 truncate 应用到每个组件:

Just apply truncate to each of the components:

let CamPosition = SCNVector3(
    transform.m41.truncate(places: 2),
    transform.m42.truncate(places: 2),
    transform.m43.truncate(places: 2)
)
print(CamPosition)

因为这些组件接受 Float 值，您还应该将扩展名更改为:

Because these components take in Float values, you should also change your extension to this:

extension Float {
    func truncate(places: Int) -> Float {
        return Float(floor(pow(10.0, Float(places)) * self)/pow(10.0, Float(places)))
    }
}

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