IN THIS BLOG, YOU CAN ALWAYS CLICK ON PICTURES TO ZOOM!
The problem was: the plotter makes dots from left to right, line by line, then goes to next line, etc.
It was a problem because one could see these lines and their limits/visual artefacts, when the pen’s paint flow slightly rises up or slows down.
How to solve that? I just programmed the drawing such as every point is made in a random order, and then: magic! everything disappears (see the video).