Thanks for sharing Zachary. Good pointers.

I assume using normal 2d array to store the data as per this youtube https://www.youtube.com/watch?v=E2NTCmEsdSE&t=17m05s will have the same issue?

It will be great to put into image data. I'll try to check out how to do it. Are you referring to using "UIGraphicsImageRenderer"? If you can provide pointers of where I can read up, that will help further.

By doing so, is it still easy for one to edit, undo (remove the lines) as one can do that in the 2d array?

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