To create the look of wood, we can start by creating a virtual "log" with perfectly cylindrical growth rings. Then, we'll take a slice of the log and perturb the growth rings using noise from our noise texture.
The following diagram illustrates our virtual log. It is aligned with the y axis, and extends infinitely in all directions. The growth rings are aligned with integer distances from the y axis. Each ring is given a darker color, with a lighter color in-between rings. Each growth ring spans a narrow distance around the integer distances:
To take a "slice," we'll simply define a 2D region of the log's space ...
