title: c++ 2D array non-regular grid interpolation
body: <p>I got a non regular 2D array.</p>
  
  <p>Here's some parts of the arrray, using "nearest neighbor" interpolation.</p>
  
  <p><img src="https://i.stack.imgur.com/C73it.png" alt="nearest neighbor sample">
  <img src="https://i.stack.imgur.com/IQbcG.png" alt="Somewhere else on the grid..."></p>
  
  <p>I would like to go from that :</p>
  
  <p><img src="https://i.stack.imgur.com/tdv5d.png" alt="nearest neighbor interpolation">
  to that :
  <img src="https://i.stack.imgur.com/LKKss.png" alt="bicubic interpolation"></p>
  
  <p>I can't use bicubic interpolation, because my grid is not regular.</p>
  
  <p>What can I use ? (need to be fast - realtime render...)</p>