Add a cancellable despawn event- allows mods to decide to prevent the despawning

of certain otherwise normally despawnable mobs.

common/net/minecraftforge/event/ForgeEventFactory.java

@@ -13,6 +13,7 @@ import net.minecraftforge.common.MinecraftForge;
 import net.minecraftforge.event.Event.Result;
 import net.minecraftforge.event.entity.living.LivingPackSizeEvent;
 import net.minecraftforge.event.entity.living.LivingSpawnEvent;
+import net.minecraftforge.event.entity.living.LivingSpawnEvent.AllowDespawn;
 import net.minecraftforge.event.entity.player.PlayerDestroyItemEvent;
 import net.minecraftforge.event.entity.player.PlayerEvent;
 import net.minecraftforge.event.entity.player.PlayerInteractEvent;
@@ -59,6 +60,11 @@ public class ForgeEventFactory
         return MinecraftForge.EVENT_BUS.post(new LivingSpawnEvent.SpecialSpawn(entity, world, x, y, z));
     }
 
+    public static boolean canEntityDespawn(EntityLiving entity)
+    {
+        return !MinecraftForge.EVENT_BUS.post(new AllowDespawn(entity));
+    }
+    
     public static List getPotentialSpawns(WorldServer world, EnumCreatureType type, int x, int y, int z, List oldList)
     {
         WorldEvent.PotentialSpawns event = new WorldEvent.PotentialSpawns(world, type, x, y, z, oldList);

common/net/minecraftforge/event/entity/living/LivingSpawnEvent.java

@@ -47,4 +47,25 @@ public class LivingSpawnEvent extends LivingEvent
             super(entity, world, x, y, z);
         }
     }
+    
+    /**
+     * Fired if the mob may be allowed to despawn. Cancellation will prevent possible despawning. This is fired every tick for 
+     * every despawnable entity. Be efficient in your handlers.
+     * 
+     * Note: this is not fired <em>if</em> the mob is definitely going to otherwise despawn. It is fired to check if
+     * the mob can be allowed to despawn according to standard mob spawning rules. See {@link EntityLiving#despawnEntity}
+     * 
+     * @author cpw
+     *
+     */
+    @Cancelable
+    public static class AllowDespawn extends LivingSpawnEvent
+    {
+
+        public AllowDespawn(EntityLiving entity)
+        {
+            super(entity, entity.worldObj, (float)entity.posX, (float)entity.posY, (float)entity.posZ);
+        }
+        
+    }
 }

patches/minecraft/net/minecraft/entity/EntityLiving.java.patch

@@ -1,14 +1,17 @@
 --- ../src_base/minecraft/net/minecraft/entity/EntityLiving.java
 +++ ../src_work/minecraft/net/minecraft/entity/EntityLiving.java
-@@ -31,6 +31,7 @@
+@@ -31,6 +31,10 @@
  import net.minecraft.util.MathHelper;
  import net.minecraft.world.World;
  import net.minecraft.world.WorldServer;
 +import net.minecraftforge.common.ForgeHooks;
++import net.minecraftforge.common.MinecraftForge;
++import net.minecraftforge.event.ForgeEventFactory;
++import net.minecraftforge.event.entity.living.LivingSpawnEvent.AllowDespawn;
  
  public abstract class EntityLiving extends EntityLivingBase
  {
-@@ -141,6 +142,7 @@
+@@ -141,6 +145,7 @@
      public void setAttackTarget(EntityLivingBase par1EntityLivingBase)
      {
          this.attackTarget = par1EntityLivingBase;
@@ -16,7 +19,18 @@
      }
  
      /**
-@@ -726,8 +728,6 @@
+@@ -548,6 +553,10 @@
+     protected void despawnEntity()
+     {
+         if (this.persistenceRequired)
++        {
++            this.entityAge = 0;
++        }
++        else if (this.canDespawn() && !ForgeEventFactory.canEntityDespawn(this))
+         {
+             this.entityAge = 0;
+         }
+@@ -726,8 +735,6 @@
          return this.worldObj.checkNoEntityCollision(this.boundingBox) && this.worldObj.getCollidingBoundingBoxes(this, this.boundingBox).isEmpty() && !this.worldObj.isAnyLiquid(this.boundingBox);
      }