title: How does the coordinate system in an CGContextRef look like?
body: <p>I assume that the origin is on the bottom left, and the y-axis expands up, starting from 0.
  The x-axis expands to the right, starting from 0.</p>
  
  <p>I just ask because I get very weird results from my drawing code... want to make sure that I didn't get this part wrong.</p>