The world begins with a seed

Every Sunfallow world begins with a seed: a number, or any text that is turned into a number. The same seed with the same size and the same generator version produces the same world, every time.

Only your changes are saved

Because the world can be rebuilt from its seed, a save does not store the landscape. It stores what you changed: buildings, felled trees, planted fields, containers. This keeps saves small and means that the world and your changes can be told apart.

The world is cut into chunks of 32 × 32 tiles. Chunks around the camera are generated on worker threads and the ones far away are unloaded, so the window stays smooth while the world is made.

How a world is made

The second generation, introduced in version 0.3.0, works in layers:

1. Continents, mountain chains and island groups are shaped first. The sea surrounds them.
2. Climate follows: the north is cold, the south is hot, and high ground is colder.
3. Water. The generator fills hollows in the terrain and counts how much water flows through every point. Where enough flows, a river appears, with tributaries that merge and a mouth that widens. Lakes get outflows.
4. Biomes, 25 above the surface, are placed from climate and moisture.
5. Settlements and roads (added in the third generation) and exploration sites come last.

Old worlds stay safe

A better generator would normally change every world made with the old one. To prevent that, each generator version is frozen once it is replaced, and the test suite compares the output of every version with recorded SHA-256 fingerprints. If a change alters even one frozen world, the test fails.

Limits

• Worlds are finite and surrounded by the sea. New worlds can reach 16,384 × 16,384 tiles.
• The rivers follow a simple physical idea. This is not a scientific climate or erosion model.
• Terrain features such as cliffs, ravines, deltas and waterfalls are still on the roadmap, not in the game.

You can see what the generator makes in the biome atlas.