Creating a wood-grain effect
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 image 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 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 based on ...