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Caves ​

Caves are used to make the underground more interesting.

Overworld Generation ​

Caves are not noise based, but instead work by carving the terrain out between a random amount of nodes. It gets its own dedicated PRNG object when initialized.

Setup ​

The world seed and the relevant chunk position are used to determine the seed of the cave.

cpp
int32_t carveExtent = 8;
// Use the world seed to init the PRNG
rand.setSeed(world.seed);
int64_t xOffset = rand.nextLong() / 2 * 2 + 1;
int64_t zOffset = rand.nextLong() / 2 * 2 + 1;
// Iterate beyond the current chunk by 8 chunks in every direction
for (int32_t cXoffset = cX - carveExtent; cXoffset <= cX + carveExtent; ++cXoffset) {
  for (int32_t cZoffset = cZ - carveExtent; cZoffset <= cZ + carveExtent; ++cZoffset) {
    rand.setSeed(((int64_t(cXoffset) * xOffset) + (int64_t(cZoffset) * zOffset)) ^ world.seed);
    GenerateCaves(cXoffset, cZoffset, cX, cZ, c);
  }
}

From here, a number in the range of 0 - 42 is generated, by feeding the generation result into itself 3 times and adding 1 after each result.

cpp
int32_t numberOfCaves = rand.nextInt(rand.nextInt(rand.nextInt(40) + 1) + 1);

This number is reset to 0 if the next random number between 0 and 15 isn't equal to 0.

Carving ​

The resulting number of caves are then iterated over.

cpp
double xOffset = double(cXoffset * CHUNK_WIDTH_X + rand.nextInt(CHUNK_WIDTH_X));
double yOffset = double(rand.nextInt(rand.nextInt(120) + 8));
double zOffset = double(cZoffset * CHUNK_WIDTH_Z + rand.nextInt(CHUNK_WIDTH_Z));
int32_t numberOfNodes = 1;
if(rand.nextInt(4) == 0) {
    CarveCave(cX, cZ, c, xOffset, yOffset, zOffset);
    numberOfNodes += rand.nextInt(4);
}

The resulting number of nodes is then iterated over, while still inside of the cave loop.

cpp
float carveYaw = rand.nextFloat() * float(M_PI) * 2.0F;
float carvePitch = (rand.nextFloat() - 0.5F) * 2.0F / 8.0F;
float tunnelRadius = rand.nextFloat() * 2.0F + rand.nextFloat();
CarveCave(
    cX, cZ, c,
    xOffset, yOffset, zOffset,
    tunnelRadius, carveYaw, carvePitch,
    0, 0, 1.0D
);

MISSING

This algorithm is difficult to not express as just code, and I hate that.

Nether Generation ​

OverworldNether
StoneNetherrack
Water (Flowing)Lava (Flowing)
Water (Still)Lava (Still)

The checks for Dirt and Grass still exist, though neither are replenished, and Lava isn't placed at the bottom of the world.

Further reading ​