Introduction

It's easy to use shaders to create a smooth-looking surface, but that is not always the desired goal. If we want to create realistic-looking objects, we need to simulate the imperfections of real surfaces. That includes things such as scratches, rust, dents, and erosion. It is somewhat surprising how challenging it can be to make surfaces look like they have really been subjected to these natural processes. Similarly, we sometimes want to represent natural surfaces such as wood grain or natural phenomena such as clouds to be as realistic as possible without giving the impression of them being synthetic or exhibiting a repetitive pattern or structure.

Most effects or patterns in nature exhibit a certain degree of randomness and non-linearity. Therefore, you might imagine that we could generate them by simply using random data. However, random data such as the kind that is generated from a pseudo-random number generator is not very useful in computer graphics. There are two main...