StretchedBillboard 实现

            Vector3 rightward = transform.parent.forward;

            if (isShowLeft) rightward = -rightward;

            Vector3 forward = (Camera.current.transform.position - transform.position).normalized;

            if (isShowBack) forward = -forward;

            float cosVal = Vector3.Dot(rightward, forward);

            if (Mathf.Abs(cosVal) >= 0.999999f) return;

            rightward = rightward * cosVal;

            forward = forward - rightward;

            //不能用forward改变,不能保证right朝向 有时候会反过来

            if (cosVal > 0)

                transform.rotation = Quaternion.LookRotation(forward, Vector3.Cross(rightward, forward));

            else

                transform.rotation = Quaternion.LookRotation(forward, Vector3.Cross(forward, rightward));

            //角度旋转

            if (billboardAngle != 0)

            {

                Vector3 oriAngle = transform.eulerAngles;

                oriAngle.x += billboardAngle;

                transform.eulerAngles = oriAngle;

            }