Added custom world generator API

By: Dinnerbone <dinnerbone@dinnerbone.com>

paper-api/src/main/java/org/bukkit/generator/BlockPopulator.java

@@ -0,0 +1,20 @@
+package org.bukkit.generator;
+
+import java.util.Random;
+import org.bukkit.Chunk;
+import org.bukkit.World;
+
+/**
+ * A block populator is responsible for generating a small area of blocks.
+ * For example, generating glowstone inside the nether or generating dungeons full of treasure
+ */
+public interface BlockPopulator {
+    /**
+     * Populates an area of blocks at or around the given chunk
+     *
+     * @param world The world to generate in
+     * @param random The random generator to use
+     * @param chunk The chunk to generate for
+     */
+    public void populate(World world, Random random, Chunk source);
+}

paper-api/src/main/java/org/bukkit/generator/ChunkGenerator.java

@@ -0,0 +1,54 @@
+package org.bukkit.generator;
+
+import java.util.List;
+import java.util.Random;
+import org.bukkit.World;
+
+/**
+ * A chunk generator is responsible for the initial shaping of an entire chunk.
+ * For example, the nether chunk generator should shape netherrack and soulsand
+ */
+public interface ChunkGenerator {
+    /**
+     * Shapes the chunk for the given coordinates.<br />
+     * <br />
+     * This method should return a byte[32768] in the following format:
+     * <pre>
+     * for (int x = 0; x < 16; x++) {
+     *     for (int z = 0; z < 16; z++) {
+     *         for (int y = 0; y < 128; y++) {
+     *             // result[(x * 16 + z) * 128 + y] = ??;
+     *         }
+     *     }
+     * }
+     * </pre>
+     *
+     * Note that this method should <b>never</b> attempt to get the Chunk at
+     * the passed coordinates, as doing so may cause an infinite loop
+     *
+     * @param world The world this chunk will be used for
+     * @param random The random generator to use
+     * @param x The X-coordinate of the chunk
+     * @param z The Z-coordinate of the chunk
+     * @return byte[] containing the types for each block created by this generator
+     */
+    public byte[] generate(World world, Random random, int x, int z);
+
+    /**
+     * Tests if the specified location is valid for a natural spawn position
+     *
+     * @param world The world we're testing on
+     * @param x X-coordinate of the block to test
+     * @param z Z-coordinate of the block to test
+     * @return true if the location is valid, otherwise false
+     */
+    public boolean canSpawn(World world, int x, int z);
+
+    /**
+     * Gets a list of default {@link BlockPopulator}s to apply to a given world
+     *
+     * @param world World to apply to
+     * @return List containing any amount of BlockPopulators
+     */
+    public List<BlockPopulator> getDefaultPopulators(World world);
+}