title: In a triangulated isometric grid, what triangle is a given point in?
body: <p>I have a triangulated isometric grid, like this:
  <a href="https://i.stack.imgur.com/uCx7k.gif" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/uCx7k.gif" alt="alt text" /></a><br />
  <sub>(source: <a href="https://web.archive.org/web/20160328125659/http://mathforum.org/workshops/sum98/participants/sanders/isomgrid.gif" rel="nofollow noreferrer">mathforum.org</a>)</sub></p>
  <p>In my code, triangles are grouped by columns.</p>
  <p>As I hover the mouse, I want to calculate what triangle the mouse coordinates are in. Is there a simple algorithm to do that?</p>