Return true if a point p is not a valid point on a side of the triangle (0,0)-(1,0)-(0,1).
This is not a complete test (for example, it does not check if y = 1 - x for points on the hypotenuse). The point of this is to exclude the kinds of invalid points we are likely to see, not all of them.
Note that we use (-1, -1) to indicate "invalid" points in the rest of the code and these are easy to detect: they require only one comparison.
Definition at line 109 of file grounded_cell_fraction.cc.
References pism::Point::x, and pism::Point::y.
Referenced by grounded_area_fraction().