title: Swift SKSpriteNode: Chaining Sprites by Image Feature
body: <h1>Context</h1>
  <p>For the purpose of a MWE we will be using the following image of a stick figure:
  <a href="https://i.stack.imgur.com/rlcYZ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/rlcYZ.png" alt="enter image description here" /></a></p>
  <p>with the goal of having a chain of these sprites move, hand-in-hand, across the screen:
  <a href="https://i.stack.imgur.com/6bhQb.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/6bhQb.png" alt="enter image description here" /></a></p>
  <p>It is worthwhile to note that the stick figure image itself is wider than the arm-span of this stick figure. The background is, however, transparent.</p>
  <p>Depending on the application, one may make a class that either inherits from <code>SKSpriteNode</code> or encapsulates it, e.g. a class called <code>Person</code>, to store additional information, where there may be an array <code>var people = [Person]()</code>.</p>
  <h1>Questions</h1>
  <p>1.) Suppose you had two instances of the aforementioned <code>Person</code> class with each sprite taking a stick figure image. How could one position them - programmatically - such that the sprites are touching ''hand in hand'' although the image has a transparent background? Of course one could spend some time fiddling about to get find a spacing parameter to ensure this is achieved, but that parameter would always have to be, via trial-and-error, re-calculated if the sprites were re-scaled.</p>
  <p>2.) Given a chain of these sprites, hand in hand, how could one animate them to move across the screen at the same velocity?  If one calculates the spacing parameter alluded to in 1.) then an <code>SKAction</code> could be given to each <code>Person</code> such that their end position is offset (but total distance traveled is the same), where the TimeInterval is maintained the same. Is there a way to tell all the sprites to move to the left until off the screen at a rate of $x$ pixels per second?</p>