How start a animation in a certain time?
<p>I have a CABasicAnimation involving multiple shapes that shows a transition between two different navigations. It's essentially a morph with an x duration.
However, there are a couple of requirements that I don't know how to deal with (and my googlefu isn't helping)</p>

<ul>
<li><p>I need to be able to show an arbitrary point of the animation. For instance, if I'm mid-swipe between two views I need to be able to show the animation at 50%.</p></li>
<li><p>I need to be able to start the animation at an arbitrary point. In the previous case, if I'm mid-swipe and release the view I need to be able to complete the animation from 50% to 100%.
I gave it a shot with timeSincePause (code) but I can't get anywhere with the animation.</p></li>
</ul>

<p>As an aid I have these two methods, </p>

<p>If the method of <strong>Resume</strong> an animation is an implicit way of continuing the same from a certain point with difference that is continuous from a time <strong>X</strong> which is defined by the <strong>pause</strong> method, how can I get it to NOT be the pause method that defines Continue <strong><em>beginTime</em></strong> if not already determined</p>

<pre><code>@IBAction func tapPause() {
    let pausetime = shape.convertTime(CACurrentMediaTime(), from: nil)
    shape.speed = 0.0
    shape.timeOffset = pausetime
 }

@IBAction func tapResume() {
   let pausedTime = shape.timeOffset
   shape.speed = 1.0
   shape.timeOffset = 0.0
   shape.beginTime = 0.0

   let timeSincePause = shape.convertTime(CACurrentMediaTime(), from: nil) - pausetime
   shape.beginTime = timeSincePause
 }
</code></pre>

<p>Which methods should I research to get this done?</p>