<  ? php
$_SESSION['lines'] = array();
//            array(x1, y1, z1, x2, y2, z2)
$_SESSION['lines'][] = array(32, 32,  0,  0,  0,  0);
$_SESSION['lines'][] = array(32,  0,  0,  0, 32,  0);
$_SESSION['lines'][] = array(10,  0,  0, 15,  0,  0);
$_SESSION['lines'][] = array(10,  1,  0, 15,  1,  0);

//check if the lines intersect...
function intersect($a)
{
  $r = array();
  for($i = count($a)-1; $i >= 0; --$i)
  {
    for($j = $i-1; $j >= 0; --$j)
    {
      $x11 = $a[$i][0];
      $y11 = $a[$i][1];
      $z11 = $a[$i][2];
      $x12 = $a[$i][3];
      $y12 = $a[$i][4];
      $z12 = $a[$i][5];

      $x21 = $a[$j][0];
      $y21 = $a[$j][1];
      $z21 = $a[$j][2];
      $x22 = $a[$j][3];
      $y22 = $a[$j][4];
      $z22 = $a[$j][5];

      $a1 = $y12 - $y11;
      $b1 = $x11 - $x12;
      $c1 = $a1 * $x11 + $b1 * $y11;
      $a2 = $y22 - $y21;
      $b2 = $x21 - $x22;
      $c2 = $a2 * $x21 + $b2 * $y21;

      $d = $a1 * $b2 - $a2 * $b1;
      if($d == 0)
      {
        echo('lines parallel\n');
      }
      else
      {
        $xLoc = ($b2 * $c1 - $b1 * $c2) / $d;
        $yLoc = ($a1 * $c2 - $a2 * $c1) / $d;
        printf("lines %d and %d intersect at (%d, %d)\n", $i, $j, $xLoc, $yLoc);
      }
    }
  }
  return $r;
}

intersect($_SESSION['lines']);
?>