Question about Vector2f.getAngle()


I was wondering why the method getAngle() of the Vector2f class return a negative angle on a vector (1, 1) and a positive angle on a vector(-1, -1).

I’m not very good at trigonometric, but I thought that vectors with positive “y” coordinate had positive angle, and negative “y” had negative angle.

here is the Vector2f code, where I don’t understand the negation of the atan2(). Thanks for your explanations.

public float getAngle() {
return -FastMath.atan2(y, x);