That's a nice way of looking at it. The trick of adding 1 to the real part doesn't work in the degenerate case where y=-x. In that case, as I said in my earlier

That's a nice way of looking at it. The trick of adding 1 to the real part doesn't work in the degenerate case where y=-x. In that case, as I said in my earlier comment, an alternative formula is PERP(y)(yx+|yx|). Both formulas need to be used in practice, depending on which one is closer to giving a degenerate answer.