If you really want to check colinearity of three points, you can just multiply vectors: 
sub isCorrectPath () {
  my ($x1, $y1, $x2, $y2, $x, $y) = @_;
  return !(($x2-$x1)*($y-$y1)-($x-$x1)*($y2-$y1));
}

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In reply to Re: Check if line is straight by pajout
in thread Check if line is straight by Anonymous Monk

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