How to move a rotated SCNNode in SceneKit?

Question

The image below shows a rotated box that should be moved horizontally on the X and Z axes. Y should stay unaffected to simplify the scenario. The box could also be the SCNNo

Answer 1

Building on @Sulevus's correct answer, here's an extension to SCNNode that simplifies things by using the convertVector rather than the convertPosition transformation, in Swift.

I've done it as a var returning a unit vector, and supplied an SCNVector3 overload of multiply so you can say things like

let action = SCNAction.move(by: 2 * cameraNode.leftUnitVectorInParent, duration: 1)


public extension SCNNode {
    var leftUnitVectorInParent: SCNVector3 {
        let vectorInSelf = SCNVector3(x: 1, y: 0, z: 0)
        guard let parent = self.parent else { return vectorInSelf }
        // Convert to parent's coord system
        return parent.convertVector(vectorInSelf, from: self)
    }
    var forwardUnitVectorInParent: SCNVector3 {
        let vectorInSelf = SCNVector3(x: 0, y: 0, z: 1)
        guard let parent = self.parent else { return vectorInSelf }
        // Convert to parent's coord system
        return parent.convertVector(vectorInSelf, from: self)
    }

    func *(lhs: SCNVector3, rhs: CGFloat) -> SCNVector3 {
        return SCNVector3(x: lhs.x * rhs, y: lhs.y * rhs, z: lhs.z * rhs)
    }
    func *(lhs: CGFloat, rhs: SCNVector3) -> SCNVector3 {
        return SCNVector3(x: lhs * rhs.x, y: lhs * rhs.y, z: lhs * rhs.z)
    }
}