How to rotate an SCNBox

问题

I'm trying to rotate an SCNBox I created using swipe gestures. For example, when I swipe right the box should rotate 90degs in the Y-axis and -90degs when I swipe left. To achieve this I have been using the node's SCNAction.rotateByX method to perform the rotation animation. Now the problem I'm having is when rotating along either the X-axis or Z-axis after a rotation in the Y-axis and vice-versa is that the positions of the axes change.

What I have notice is that any rotation perform on either of the X,Y,Z axes changes the direction in which the other axes point.

Example: Default position

Then after a rotation in the Z-axis:

Of course this pose a problem because now when I swipe left or right I no longer get the desire effect because the X-axis and Y-axis have now swapped positions. What I would like to know is why does this happen? and is there anyway to perform the rotation animation without it affecting the other axes?

I apologize for my lack of understanding on this subject as this is my first go at 3d graphics.

Solution:

func swipeRight(recognizer: UITapGestureRecognizer) {
  // rotation animation
  let action = SCNAction.rotateByX(0, y: CGFloat(GLKMathDegreesToRadians(90)), z: 0, duration: 0.5)
  boxNode.runAction(action)

  //repositoning of the x,y,z axes after the rotation has been applied
  let currentPivot = boxNode.pivot
  let changePivot = SCNMatrix4Invert(boxNode.transform)
  boxNode.pivot = SCNMatrix4Mult(changePivot, currentPivot)
  boxNode.transform = SCNMatrix4Identity
}

I haven't ran into any problems yet but it may be safer to use a completion handler to ensure any changes to X,Y,Z axes are done before repositioning them.

回答1:

I had the same issue, here's what I use to give the desired behavior:

func panGesture(sender: UIPanGestureRecognizer) {
    let translation = sender.translationInView(sender.view!)

    let pan_x = Float(translation.x)
    let pan_y = Float(-translation.y)
    let anglePan = sqrt(pow(pan_x,2)+pow(pan_y,2))*(Float)(M_PI)/180.0
    var rotVector = SCNVector4()

    rotVector.x = -pan_y
    rotVector.y = pan_x
    rotVector.z = 0
    rotVector.w = anglePan

    // apply to your model container node
    boxNode.rotation = rotVector

    if(sender.state == UIGestureRecognizerState.Ended) {
        let currentPivot = boxNode.pivot
        let changePivot = SCNMatrix4Invert(boxNode.transform)
        boxNode.pivot = SCNMatrix4Mult(changePivot, currentPivot)
        boxNode.transform = SCNMatrix4Identity
    }
}

来源：https://stackoverflow.com/questions/38834092/how-to-rotate-an-scnbox

标签

ios

swift

rotation

scenekit