title: SpriteKit - get absolute size of SKNode
body: <p>I'm programming a small game in Swift and <code>SpriteKit</code>, which is made of a boxes (4 * 8).</p>
  
  <pre><code>Scene (1024 * 768)
      boxes (964 * 452)
          row1 (932 * 25)
              col1 (24 * 116)
              col2 (24 * 116)
              col3 (24 * 116)
              ...
          row2...
  </code></pre>
  
  <p>I want to give them a texture, but I don't know how big the image file should be. And the box node's size seems to be relative to its parent node. How can I get the absolute size of an <code>SKNode</code>, the size the node takes on the screen?</p>