Everything we are doing so far is on a flat plane. vPos.x and vPos.y vary, but vPos.z is always zero.
Yet the noise function actually takes a 3D point as its argument, and we can use this fact to create animated textures. If we animate the z coordinate of its argument, we end up essentially sliding the noise function in z over time.
You can think of this as taking different planar slices through some solid textured material. As you slide your plane through the texture, you uncover different layers of the texture, so the texture you see will change over time.
For lesson 18 we do just this. By animating the z coordinate of our argument to the noise function, we end up varying the value of the noise over time. The result is that the texture that is causing our disk to look bumpy will animate.
You can see this lesson by CLICKING HERE.