code: function setPos(id, x, y) {
          pos[3 * id] = x;
          pos[3 * id + 1] = y;
        }
docs: /*
  0--1------------------------------2--3
  |  |                              |  |
  4--5------------------------------6--7
  |  |                              |  |
  |  |                              |  |
  |  |                              |  |
  8--9-----------------------------10--11
  |  |                              |  |
  12-13----------------------------14--15