Various Things in MetaPost (2019)

Summary

What is the best tool to use for drawing vector pictures? For me and probably for many others, the answer is pretty obvious: Illustrator, or, maybe, Inkscape. At least that's what I thought when I was asked to draw about eight hundred diagrams for a physics textbook. Nothing exceptional, just a bunch of black and white illustrations with spheres, springs, pulleys, lenses and so on. By that time it was already known that the book was going to be made in LaTeX and I was given a number of MS Word documents with embedded images. Some of them were scanned pictures from other books, some were pencil drawings. Picturing days and nights of inkscaping this stuff made me feel dizzy, so soon I found myself fantasizing about a more automated solution. For some reason MetaPost became the focus of these fantasies. The main advantage of using MetaPost (or similar) solution is that every picture can be a sort of function of several variables. Such a picture can be quickly adjusted for any unforeseen circumstances of the layout, without disrupting important internal relationships of the illustration (something I was really concerned about), which is not easily achieved with more traditional tools. Also, recurring elements, all these spheres and springs, can be made more visually interesting than conventional tools would allow with the same time constraints. I wanted to make pictures with some kind of hatching, not unlike what you encounter in old books. First, I needed to be able to produce some curves of varying thickness. The main complication here is to construct a curve that follows the original curve at a varying distance. I used probably the most primitive working method, which boils down to simply shifting the line segments connecting Bezier curve control points by a given distance, except this distance varies along the curve. In most cases, it worked OK. Example codeFrom here on it is assumed that the library is downloaded and input fiziko.mp; is present in the MetaPost code...