AquilaX's development blog

A function in PHP to check if a point is in triangle.

  function fAB($t, $x, $y) {
    return ($y - $t['y1'])*($t['x2'] - $t['x1'])
      -($x - $t['x1'])*($t['y2'] - $t['y1']);
  }

  function fBC($t, $x, $y) {
    return ($y-$t['y2'])*($t['x3']-$t['x2'])
      -($x-$t['x2'])*($t['y3']-$t['y2']);
  }

  function fCA($t, $x, $y) {
    return ($y-$t['y3'])*($t['x1']-$t['x3'])
      -($x-$t['x3'])*($t['y1']-$t['y3']);
  }

  function CheckPointInside($t, $x, $y) {
    if (fAB($t, $x, $y)*fBC($t, $x, $y)>0 
      && fBC($t, $x, $y)*fCA($t, $x, $y)>0) {
      return true;
    } else {
      return false;
    }
  }

Function CheckPointInside expects three parameters: $t an associative array of triangle’s coordinates written as x1,y1, x2, y2, x3, y3 and $x, $y, the point’s coordinates.