Swift - How to change the Pivot of a SCNNode object

pivot, scenekit, swift

Solution

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:

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.

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

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.

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.

Problem

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