Cannot run sample code on macOS

[melMass]

Hello Trying to run the doc example:

import taichi as ti
ti.init()
from fractal import fractalClass
f = fractalClass(512)
f.draw()

results in the following error:

Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/Users/user-14/Library/Preferences/houdini/19.0/taichi_houdini/Libs/python/fractal.py", line 26, in draw
    gui = ti.GUI("Julia Set", res=(self.res * 2, self.res))
  File "/Users/user-14/Library/Preferences/houdini/19.0/taichi_houdini/bundled-packages/taichi/misc/gui.py", line 95, in __init__
    fast_gui, fast_buf)
RuntimeError: Caught an unknown exception!