title: Perlin Noise: Calculating pseudorandom gradients of grid points
body: <p>I seem to be having a bit of an issue understanding <a href="http://webstaff.itn.liu.se/~stegu/TNM022-2005/perlinnoiselinks/perlin-noise-math-faq.html#toc-algorithm" rel="nofollow noreferrer">this</a> Perlin Noise article.  I need some help understanding how calculating the pseudorandom gradients for each bounding point works.  The author gives the function:</p>
  
  <pre><code>g(xgrid, ygrid) = (gx, gy)
  </code></pre>
  
  <p>Then he gives the image:</p>
  
  <p><img src="https://i.stack.imgur.com/kwesV.gif" alt="4 pseudorandom gradients?"></p>
  
  <p>I understand the rest of the article, but I have no idea how he generates these random gradients from each bounding point.  Assistance would be greatly appreciated.  Thanks!</p>