http://teanmoon.blogspot.com/2016/04/the-bump-texture.html

What is it? The bump controls the “roughness” of your object in game. It is sometimes referred to as a normal map. It is called the DST image in Sims 4 Studio for both CAS and Build objects.

Wait, what’s a normal? The objects in The Sims are made of little flat triangles (polys). Light bounces off these flat surfaces in a given direction.

This gnome statue is made up of a bunch of different size triangles. Each triangle is a poly. One poly is outlined in red.

Light comes in and bounces off of a poly. The game knows how each poly is tilted by the normal for each poly.

Each poly in a mesh has a normal sticking straight out of it, like the arrows on this curve.

The direction the light bounces is described by the surface’s normal. Each mesh carries information about each poly’s normal, which helps the game generate shadows on it.

Each one of the blue lines pointing out of this gnome is a normal.

Bump/normal maps also contain information about normals, but instead each normal being linked to a particular poly, the normal is linked to a pixel.

Why is this a good thing?

High poly objects generate shadows really beautifully in game, but they are difficult for your computer to render.

Low poly objects can look blobby or too smooth in comparison.

Bump maps are a type of texture that allows the low poly objects to look more like a high poly version. There are more pixels covering an object than there are polys. This means that by using a bump map light can bounce many different directions off of one poly!

The bump map’s job is to create shadows to make things appear more detailed and more 3D than they actually are!