如何使用 Apple 的 SIMD 库围绕 Y 旋转 arkit 4x4 矩阵? [英] How do I rotate an arkit 4x4 matrix around Y using Apple's SIMD library?

问题描述

我正在尝试基于 ARKit 演示实现一些代码，其中有人使用此辅助函数来放置航点

I am trying to implement some code based on an ARKit demo where someone used this helper function to place a waypoint

let rotationMatrix = MatrixHelper.rotateAboutY(
    degrees: bearing * -1
)

如何使用 SIMD 库而不使用 GLKit 来实现 .rotateAboutY 函数?为了方便起见，我可以从原点开始.

How can I implement the .rotateAboutY function using the SIMD library and not using GLKit? To make it easier, I could start from the origin point.

我对矩阵数学不太熟悉，所以更基本的解释会有所帮助.

I'm not too handy with the matrix math so a more basic explanation would be helpful.

推荐答案

可能是利用内置 SIMD 库进行此类操作的最佳方式(至少，最好"的意思是自己做最少的数学运算")是用四元数表示旋转并在需要时转换为矩阵.

Probably the best way to leverage the built-in SIMD library for such operations (at least, with "best" meaning "do the least math yourself") is to express rotations with quaternions and convert to matrices when needed.

1. 构造一个 simd_quatf 表示要应用的轴角旋转.
2. 将该四元数转换为 4x4 矩阵.

1. Construct a simd_quatf representing the axis-angle rotation you want to apply.
2. Convert that quaternion to a 4x4 matrix.

您可以通过单线电话做到这一点:

You can do that with a one-line call :

let rotationMatrix = float4x4(simd_quatf(angle: radians, axis: axis))

扩展到您的rotateAboutY"案例:

Expanding to your "rotateAboutY" case:

let radians = degreesToRadians(-bearing) // degrees * .pi / 180
let yAxis = float3(0, 1, 0)
let rotationMatrix = float4x4(simd_quatf(angle: radians, axis: yAxis))

当然，一旦有了旋转矩阵，就可以使用 * 或 *= 运算符来应用它:

Of course, once you have a rotation matrix, you can apply it using the * or *= operator:

someNode.simdTransform *= rotationMatrix

如果你发现自己经常做这样的事情，你可能想在 float4x4 上写一个扩展.

If you find yourself doing something like this often, you might want to write an extension on float4x4.

_{提示:顺便说一下，在 Swift(或 C++ 或 Metal 着色器语言)中，大多数(但不是全部)SIMD 类型和全局函数不需要 simd_ 前缀.}

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