Masks from terrain in Gaea: slope, flow and deposits

This lesson is about letting the terrain itself say where grass, rock and sand belong. A terrain generator such as Gaea can turn its terrain into masks: grayscale maps of height, slope, water flow and deposits. You’ll see which masks there are and how they are computed, how to combine and export them, and how they become ground layers and placement rules in the engine.

Why this matters

In the lesson on ground material, the rules looked at two numbers for every point: its slope and its height. That is all an engine knows about a single pixel of ground. The generator knows much more, because it sees the whole terrain at once and has run the water over it. It knows which gullies collect the rain of a whole valley, where that water slowed down and dropped its sand, and where soil gathered in hollows.

In nature, exactly these things decide where sand, gravel and bare rock lie (the lesson on landforms). Masks carry this knowledge from the generator into the engine. Without them, the sand lies where an artist guessed it might.

Further in the article

1. A mask: one question, answered in gray
2. Masks that measure the shape
3. Masks that remember water: flow and deposits
4. A small recipe: masks for the ground layers
5. Getting masks out of Gaea
6. Masks in the engine
7. Where it breaks
8. Connections: the same idea in other fields
9. Sources and further reading
10. Key points
11. Test yourself