ti.ui.Camera.track_user_inputs without mouse movement will revert front vector when it is (0, 0, 1)

[YouJiacheng]

And this is the default value of front vector(postion=(0,0,0), lookat=(0,0,1))

import taichi as ti
from taichi.ui.utils import euler_to_vec, vec_to_euler
ti.init()
euler_to_vec(*vec_to_euler(ti.Vector([0, 0, 1]))) # output [-0. 0. -1.]

def vec_to_euler(v):
    v = v.normalized()
    pitch = asin(v[1])

    sin_yaw = -v[0] / cos(pitch)
    cos_yaw = -v[2] / cos(pitch)

    eps = 1e-6

    if abs(sin_yaw) < eps:
        yaw = 0
    else:
        yaw = acos(cos_yaw)
        if sin_yaw < 0:
            yaw = -yaw

    return yaw, pitch

I don't know why yaw = 0 when abs(sin_yaw) < eps.
I think using yaw = atan2(-v[0], -v[2]) can fix this problem. and simplify the code.