src/main/java/net/glowstone/generator/UndergroundGenerator.java

package net.glowstone.generator;

import java.util.Arrays;
import java.util.Map;
import java.util.Random;
import org.bukkit.Location;
import org.bukkit.Material;
import org.bukkit.World;
import org.bukkit.World.Environment;
import org.bukkit.util.noise.OctaveGenerator;
import org.bukkit.util.noise.SimplexOctaveGenerator;

/**
 * A generator for subterranean worlds, in particular the Nether.
 */
public class UndergroundGenerator extends GlowChunkGenerator {

    public UndergroundGenerator() {
        // TODO: populators
        super();
    }

    @Override
    public byte[] generate(World world, Random random, int chunkX, int chunkZ) {
        Map<String, OctaveGenerator> octaves = getWorldOctaves(world);
        OctaveGenerator noiseFloor = octaves.get("floor");
        OctaveGenerator noiseCeiling = octaves.get("ceiling");
        OctaveGenerator noiseJitter1 = octaves.get("jitter1");
        OctaveGenerator noiseJitter2 = octaves.get("jitter2");
        OctaveGenerator noiseStalactite = octaves.get("stalactite");
        OctaveGenerator noiseStalagmite = octaves.get("stalagmite");
        OctaveGenerator noisePlatform1 = octaves.get("platform1");
        OctaveGenerator noisePlatform2 = octaves.get("platform2");

        chunkX <<= 4;
        chunkZ <<= 4;

        Material stone = world.getEnvironment() == Environment.NETHER ? Material.NETHERRACK : Material.STONE;
        int height = world.getMaxHeight();

        byte[] buf = start(stone);

        for (int x = 0; x < 16; x++) {
            for (int z = 0; z < 16; z++) {
                int min = (int) (Math.abs(noiseFloor.noise(x + chunkX, z + chunkZ, 0.5, 0.5) * 3)
                        + 5 + noiseJitter1.noise(x + chunkX, z + chunkZ, 0.5, 0.5) * 2
                        + convertPointyThings(noiseStalagmite, x + chunkX, z + chunkZ, height));
                int max = (int) (height - Math.abs(noiseCeiling.noise(x + chunkX, z + chunkZ, 0.5, 0.5) * 3)
                        - 5 + noiseJitter2.noise(x + chunkX, z + chunkZ, 0.5, 0.5) * 2 - random.nextInt(5)
                        - convertPointyThings(noiseStalactite, x + chunkX, z + chunkZ, height));

                if (min > 20) {
                    min -= random.nextInt(5);
                }

                if (min >= max) {
                    set(buf, x, 0, z, Material.BEDROCK);
                    set(buf, x, height - 1, z, Material.BEDROCK);
                    continue;
                }

                for (int y = min; y <= max; y++) {
                    set(buf, x, y, z, Material.AIR);
                }

                int platform = (int) (noisePlatform1.noise(x + chunkX, z + chunkZ, 0.5, 0.5, true) * 20 - 4);
                if (platform > 5) {
                    platform -= random.nextInt(3);
                }
                while (platform-- > 0) {
                    set(buf, x, height / 2 - platform - 1, z, stone);
                }

                platform = (int) (noisePlatform2.noise(x + chunkX, z + chunkZ, 0.5, 0.5, true) * 30 - 6);
                if (platform > 5) {
                    platform -= random.nextInt(3);
                }
                while (platform-- > 0) {
                    set(buf, x, height / 4 - platform - 1, z, stone);
                }

                for (int i = 4; i > 0; i--) {
                    if (get(buf, x, i, z) == Material.AIR) {
                        set(buf, x, i, z, Material.LAVA);
                    }
                }
                set(buf, x, 0, z, Material.BEDROCK);
                set(buf, x, height - 1, z, Material.BEDROCK);
            }
        }

        return buf;
    }

    private double convertPointyThings(OctaveGenerator noise, int x, int z, int height) {
        return Math.max(noise.noise(x, z, 0.5, 0.5, true) * height * 3 / 2 - height / 2, 0);
    }

    @Override
    public Location getFixedSpawnLocation(World world, Random random) {
        while (true) {
            int x = random.nextInt(128) - 64;
            int y = 128 * 3 / 4;
            int z = random.nextInt(128) - 64;

            if (world.getBlockAt(x, y, z).isEmpty()) {
                while (world.getBlockAt(x, y - 1, z).isEmpty() && y > 0) {
                    y--;
                }
                return new Location(world, x, y, z);
            }
        }
    }

    @Override
    protected void createWorldOctaves(World world, Map<String, OctaveGenerator> octaves) {
        Random seed = new Random(world.getSeed());

        OctaveGenerator gen = new SimplexOctaveGenerator(seed, 10);
        gen.setScale(1 / 64.0);
        octaves.put("floor", gen);

        gen = new SimplexOctaveGenerator(seed, 10);
        gen.setScale(1 / 64.0);
        octaves.put("ceiling", gen);

        gen = new SimplexOctaveGenerator(seed, 5);
        gen.setScale(1 / 32.0);
        octaves.put("jitter1", gen);

        gen = new SimplexOctaveGenerator(seed, 5);
        gen.setScale(1 / 32.0);
        octaves.put("jitter2", gen);

        gen = new SimplexOctaveGenerator(seed, 10);
        gen.setScale(1 / 32.0);
        octaves.put("stalactite", gen);

        gen = new SimplexOctaveGenerator(seed, 10);
        gen.setScale(1 / 48.0);
        octaves.put("stalagmite", gen);

        gen = new SimplexOctaveGenerator(seed, 7);
        gen.setScale(1 / 32.0);
        octaves.put("platform1", gen);

        gen = new SimplexOctaveGenerator(seed, 8);
        gen.setScale(1 / 96.0);
        octaves.put("platform2", gen);
    }
    
}