Function s2::point::ordered_ccw

pub fn ordered_ccw(a: &Point, b: &Point, c: &Point, o: &Point) -> bool

ordered_ccw returns true if the edges OA, OB, and OC are encountered in that order while sweeping CCW around the point O.

You can think of this as testing whether A <= B <= C with respect to the CCW ordering around O that starts at A, or equivalently, whether B is contained in the range of angles (inclusive) that starts at A and extends CCW to C. Properties:

(1) If OrderedCCW(a,b,c,o) && OrderedCCW(b,a,c,o), then a == b (2) If OrderedCCW(a,b,c,o) && OrderedCCW(a,c,b,o), then b == c (3) If OrderedCCW(a,b,c,o) && OrderedCCW(c,b,a,o), then a == b == c (4) If a == b or b == c, then OrderedCCW(a,b,c,o) is true (5) Otherwise if a == c, then OrderedCCW(a,b,c,o) is false