Ground material: layers, slope and tiling

This lesson is about how the ground in a game gets its look. One texture can’t cover a world, so the ground is painted with several layers, and each point stores how much of every layer it has. You’ll see how layers are mixed by weight and by height, and how slope and height can paint most of a world by themselves. Then come the repeat of a texture near and far, the seam where rock meets soil, and grass that grows from a painted layer. Unreal is the main example, with notes on Unity and Godot.

Why this matters

In an open world, the ground is in almost every frame, and it stretches for kilometers. One tiled texture repeats so often that the eye starts to see the pattern. Painting every meter by hand would take years. And the ground is drawn on a large part of the screen, so every extra layer makes many pixels more expensive.

A ground material answers with one idea: several layers, a weight for each layer at every point, and rules that set the weights where painting by hand would be too slow. That solves the first two problems and keeps the third in check, as long as the layers stay few. The shape of the land is the topic of the lesson on landscape; this lesson is about its surface.

Further in the article

1. A recipe at every point: layers and weights
2. Sand settles between the stones: blending by height
3. Rules instead of a brush: an automatic material
4. Near and far: hiding the repeat
5. Where rock meets ground
6. Grass grows from a layer
7. What layers cost
8. In other engines
9. Where it breaks
10. Connections: the same idea in other fields
11. Sources and further reading
12. Key points
13. Test yourself