Added CreateSpawnPosition event.

src/main/java/net/minecraftforge/event/ForgeEventFactory.java

@@ -27,6 +27,7 @@ import net.minecraft.util.Vec3;
 import net.minecraft.world.Explosion;
 import net.minecraft.world.World;
 import net.minecraft.world.WorldServer;
+import net.minecraft.world.WorldSettings;
 import net.minecraft.world.biome.BiomeGenBase;
 import net.minecraft.world.storage.IPlayerFileData;
 import net.minecraft.world.storage.SaveHandler;
@@ -372,4 +373,9 @@ public class ForgeEventFactory
         */
         MinecraftForge.EVENT_BUS.post(new ExplosionEvent.Detonate(world, explosion, list));
     }
+
+    public static boolean onCreateWorldSpawn(World world, WorldSettings settings)
+    {
+        return MinecraftForge.EVENT_BUS.post(new WorldEvent.CreateSpawnPosition(world, settings));
+    }
 }

src/main/java/net/minecraftforge/event/world/WorldEvent.java

@@ -2,9 +2,11 @@ package net.minecraftforge.event.world;
 
 import java.util.ArrayList;
 import java.util.List;
+
 import net.minecraft.entity.EnumCreatureType;
 import net.minecraft.util.BlockPos;
 import net.minecraft.world.World;
+import net.minecraft.world.WorldSettings;
 import net.minecraft.world.biome.BiomeGenBase.SpawnListEntry;
 import net.minecraftforge.fml.common.eventhandler.Cancelable;
 import net.minecraftforge.fml.common.eventhandler.Event;
@@ -109,4 +111,19 @@ public class WorldEvent extends Event
             }
         }
     }
+
+    /**
+     * Called by WorldServer when it attempts to create a spawnpoint for a dimension.
+     * Canceling the event will prevent the vanilla code from running.
+     */
+    @Cancelable
+    public static class CreateSpawnPosition extends WorldEvent
+    {
+        public final WorldSettings settings;
+        public CreateSpawnPosition(World world, WorldSettings settings)
+        {
+            super(world);
+            this.settings = settings;
+        }
+    }
 }