calculation
All the functions in this chapter have one thing in common: They have a value-output, that means all you get from them is a number. Sounds boring, right? It isn't!
constrain()
constrain() can be used to avoid objects move out of the screen.
map()
The map()-function re-maps a number from one range to another.
pos = map(a, 0, 50, 0, width);