It works fine on macOS 69.0.3494.0 and 67.0.3396.99
Looking at the source, it wants to read a touch event whenever touch is supported (in update_mouse_position)-- but I'm using a mouse. Even though there's a touch screen, too :) (And using the touch screen, I can draw)
Either way, this is awesome - thank you for putting this together!
wow, ok I'll definitely look into it, I'm pretty sure I can get my hands on a ChromeOS box. Thank you so very much for taking the time to point out exactly at what's going on.