title: Convert UIKit coordinates to SpriteKit coordinates
body: <p>I am trying to convert normal uikit coordinates (top left origin, width and height go right and down) to Sprite Kit coordinates (origin is at center of node, left and down are negative, right and up are positive).</p>
  
  <p>Does anyone know how to do this? Unfortunately I can't work around this to my knowledge because I am using QuartzCore for drawing on a SKNode. Without converting, I am getting really off drawings. </p>