Texture Maps

This is a perfectly flat square. In 2D. With a single flat color. It has a texture applied to modify the "normals", which means light falling on it will behave as if its not flat at all, but modified to the shape of the texture. A wonderful little trick that is used all the time to speed up rendering by keeping the number of vertices and faces low.

If you look carefully at the "stones" above any of the lights, you can see the highlights at the bottom of the stones, and shadows at the top. And if you look at the stones directly under the lights, you can see no shadows at all. Just as if the stones were actually protruding from the flat surface of the wall.

Blender also lets you apply the texture directly to make the vertices on the surface actually be displaced. Which you need if you are going to look at the texture side on, and see the actual silhouettes of the bumps, for example, a mountain range. But for this you need a lot of vertices. Thousands of them. Millions. And if you want to animate that you need a whole stack of computers, which is called a "render farm". All the CGI movies you see have large render farms working for months creating all the final frames. So there are definite limits to what you can do with just one computer. Once I push this computer to the limit it will be time to buy a newer, faster one. But that will not be for a while yet. At least I hope so, my wallet isn't very fat at the moment.