question: final boolean isReflex ( EarClippingVertex vertex ) { Vector2 p = vertex . point ; Vector2 p0 = vertex . prev . point ; Vector2 p1 = vertex . next . point ; Vector2 v1 = p . to ( p0 ) ; Vector2 v2 = p . to ( p1 ) ; if ( v1 . cross ( v2 ) < 0.0 ) { return false ; } else { return true ; } }
target:  Returns true if the given vertex is a reflex vertex. <p> A reflex vertex is a vertex who's adjacent vertices create an an angle greater than 180 degrees (or the cross product is  positive) for CCW vertex winding.