title: SceneKit LookAt constraint not animating smoothly
body: <p>I am having issue with the animation of animating the look at constraint. I have a scene with multiple objects that can be tapped. Once you tap on an object, the camera's position is updated to be a certain distance from the object and a look at  constraint is applied.</p>
  
  <p>The issue is with the animation of the look at constraint in the SCNTransaction begin and commit block. I set this code to do a look at:</p>
  
  <pre><code>// Causes the camera to look at the given target
  private func cameraLookAtTarget(target: SCNNode)
  {
      let constraint = SCNLookAtConstraint(target: target)
      constraint.gimbalLockEnabled = true
      cameraNode.constraints = [constraint]
  }
  </code></pre>
  
  <p>And the block of code where this gets called when the object is tapped:</p>
  
  <pre><code>SCNTransaction.begin()
  SCNTransaction.setAnimationDuration(CAMERA_ANIMATION_DURATION)
  cameraLookAtTarget(target)
  SCNTransaction.commit()
  </code></pre>
  
  <p>The animation does a jump first and then animates to look at the object instead of smoothly rotating the camera to look at the new target. I can confirm that it is the look at constraint, since updating the camera position moves it smoothly.</p>
  
  <p>Edit: Basically, its as though the camera is being reset first in the animation and then animating to look at the target. I want the look at constraint to animate from the current object it is looking at to the new target.</p>
  
  <p>I can't figure out the problem. In Unity I can easily get a rotation that is a look rotation, and apply a slerp to it in the update method so that it slowly looks at the object.</p>