Seems cc.Vec2 signAngle behaves differently from API document, at Cocos Creator v1.6.1.
http://cocos2d-x.org/docs/api-ref/creator/v1.5/classes/Vec2.html
It should return from -MathPI to Math.PI, but sometimes returning over the limit.
ex:
returns: 5.302326843376848 v_1:(-512.16, 194.18) v_2:(-274.57, -195.38)
returns: 4.057998878913847 v_1:(-493.00, 134.00) v_2:(124.91, -304.74)
returns: -4.169044791828796 v_1:(105.18, -472.16) v_2:(-98.61, 33.13)
It seems working correctly, if add this.
if (returns > Math.PI) {
jreturns -= Math.PI * 2;
}
else if (returns < -Math.PI) {
returns += Math.PI * 2;
}
or need to update document.