support the ipycanvas widget in cocalc-jupyter

[williamstein]

See https://ipycanvas.readthedocs.io/en/latest/

[williamstein]

Probably this involves:

1. Installing all the relevant code for the upstream project, and
2. Porting the frontend code to cocalc-jupyter, since it probably (?) uses the generic widget extensions feature, which we don't support.

[sheinb]

I'd add that this would provide a very convenient way to incorporate turtle graphics in a notebook for teaching, along with efficient graphics for games and visualizations like 'game of life'.

[williamstein]

This is a custom widget, and our goal with jupyter now is that ALL custom widgets be fully supported. I just tried this and something mysterious does go wrong:

This also does not work for my in JupyterLab 3.6:

Ipycanvas is also broken for me in a fresh install with JupyterLab 4.2.3:

It does work in colab, though you have to do something special to enable it (for security reasons):

but I think colabs widgets setup is several years old (?), so it's maybe more likely to support something that used to work:

In any case, it's very likely a bug that this doesn't work, and we should support it.

Upstream issues saying this is broken on mybinder:

• Failed to load model class 'CanvasModel' from module 'ipycanvas' in Binder jupyter-widgets-contrib/ipycanvas#343

[williamstein]

!pip install ipycanvas

from ipycanvas import Canvas

canvas = Canvas(width=200, height=200)

canvas.fill_rect(25, 25, 100, 100)
canvas.clear_rect(45, 45, 60, 60)
canvas.stroke_rect(50, 50, 50, 50)

canvas

[williamstein]

This DOES work in JupyterLab 4.2.4. Definitely a bug to be fixed: