The method resetTransform of SCNPhysicsBody

According to the SceneKit document, the function of resetTransform is:

Updates the position and orientation of a body in the physics simulation to match that of the node to which the body is attached.

Through experiment, I found this is little special.

If you do this:

var node = SCNNode(geomentry: SCNBox())
node.position = SCNVector3(0, 1, 0)
node.rotation = SCNVector4(1, 0, 0, CGFloat(M_PI)/2)
node.physicsBody = SCNPhysicsBody(type: .Dynamic, nil)
scene.rootNode.addChildNode(node)

If you get the position and rotation of node.presentationNode() in the render delegate, where I mean you need to get the latest and real data, you will found the effect of the setup of node’s position and rotation is not work at the begining.

At the begining, the position will be (0, 0, 0), but not what you have set, (0, 1, 0).

If you have read the document about SCNNode.position and SCNNode.rotation, you will found:

position

The translation applied to the node. Animatable.

The Animatable means it will take several frames to get the effect.

However, it’s different when you use resetTransform of SCNPhysicsBody:

var node = SCNNode(geomentry: SCNBox())
node.position = SCNVector3(0, 1, 0)
node.rotation = SCNVector4(1, 0, 0, CGFloat(M_PI)/2)
node.physicsBody = SCNPhysicsBody(type: .Dynamic, nil)
scene.rootNode.addChildNode(node)
node.physicsBody.resetTransform()

The effect will work at the begining.

Junyuan Hong
Junyuan Hong
CSE PhD Student

My research interests include distributed learning, data privacy and deep learning.

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