Return the crossproduct of the two vectors as a Vec2.
    Cross product doesn't really make sense in 2D, but return the Z component
    of the 3d result.

def cross_v2(vec1, vec2):
    """Return the crossproduct of the two vectors as a Vec2.
    Cross product doesn't really make sense in 2D, but return the Z component
    of the 3d result.
    """

    return vec1.y * vec2.x - vec1.x * vec2.y