Swift-如何更改SCNNode对象的Pivot-Swift-HowtochangethePivotofaSCNNodeobject

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A node's pivot is a transformation matrix, the inverse of which is applied to the node before its transform property takes effect. For example, take a look at this bit from the default SceneKit Game template in Xcode:

节点的枢轴是变换矩阵，其变换在其变换属性生效之前应用于节点。例如，从Xcode中的默认SceneKit游戏模板看一下这个位：

let boxNode = SCNNode()
boxNode.geometry = SCNBox(width: 1, height: 1, length: 1, chamferRadius: 0.02)

If you set the boxNode's position, that point corresponds to the center of the cube, and if you rotate it (as the template does in an animation), it spins around its center.

如果设置boxNode的位置，则该点对应于立方体的中心，如果旋转它（如模板在动画中所做的那样），它将围绕其中心旋转。

To change the anchor point, set the pivot to a translation transform:

要更改定位点，请将数据透视表设置为平移变换：

boxNode.pivot = SCNMatrix4MakeTranslation(0.5, 0.5, 0.5)

Now, when you set the position that point corresponds to the top-right-front corner of the cube, and when you rotate the cube it spins around that corner.

现在，当您设置该点的位置对应于立方体的右上角时，并且当您旋转立方体时，它会围绕该角旋转。

More generally, a pivot transforms the contents of a node relative to the node's own transform. Suppose you wanted to model the precession of the Earth's axis of rotation. You could do this by creating two animations: one that animates pivot to spin the node around its own Y axis, and another that animates rotation to move that axis relative to the space containing the node.

更一般地，枢轴相对于节点自己的变换变换节点的内容。假设你想模拟地球旋转轴的进动。您可以通过创建两个动画来完成此操作：一个动画旋转以围绕其自己的Y轴旋转节点，另一个动画旋转以相对于包含节点的空间移动该轴。

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On the pivot topic:

在pivot主题：

Just in case you do not have dimensions for your geometry/node something like this might help (specially for SCNText).

万一你没有几何/节点的尺寸，这样的东西可能会有所帮助（特别是对于SCNText）。

var minVec = SCNVector3Zero
var maxVec = SCNVector3Zero
if node.getBoundingBoxMin(&minVec, max: &maxVec) {
  let bound = SCNVector3(
    x: maxVec.x - minVec.x,
    y: maxVec.y - minVec.y,
    z: maxVec.z - minVec.z)

  node.pivot = SCNMatrix4MakeTranslation(bound.x / 2, bound.y / 2, bound.z / 2)
}