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 the texture coordinates. Initially, the texture coordinates define a square region, with coordinates ranging from zero to one. We'll assume that the region is aligned with the x-y plane, so that the s coordinate corresponds to x, the t coordinate corresponds to y, and the value of z is zero. We can then transform this region in any way that suits...
