Nice job. There's also a good open-source ASCII paint tool which supports export to TXT/ or PNG that I've been using for the past few years as well.
Github
https://github.com/Kirilllive/ASCII_Art_Paint
Online Demo
https://kirilllive.github.io/ASCII_Art_Paint/ascii_paint.htm...
Thank yuou for sharing! Interesting solution. I'm thinking about adding brush palette.
And thank you for checking it out, glad you liked it!