Ambient Spawning and Weight Modifiers

🦇 Ambient Spawning & Weight Modifiers

Parameter	Specification Details
Spawn Injector Mixin	net.vanillaoutsider.betterbats.mixin.NaturalSpawnerMixin
Surface Spawn Mixin	net.vanillaoutsider.betterbats.mixin.BatMixin.betterbats$onCheckBatSpawnRules
Mob Category	MobCategory.AMBIENT
Vanilla Base Spawn Weight	10
Mod Default Weight	30 (better-bats:bat_spawn_weight)
Valid Surface Spawn Block Tag	#minecraft:bats_spawnable_on
Surface Spawn Sky Light	Sky Light <= 7 (Nighttime or dark forest cover)

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🌲 Dynamic Ambient Spawn Weight Replacement

In vanilla Minecraft, ambient mob spawning lists are statically fixed per biome. Better Bats utilizes NaturalSpawnerMixin to dynamically intercept NaturalSpawner.mobsAt() whenever the game checks for ambient spawns:

@Inject(method = "mobsAt", at = @At("RETURN"), cancellable = true)
private static void betterbats$onMobsAt(
        ServerLevel level, StructureManager structureManager, ChunkGenerator generator, 
        MobCategory mobCategory, BlockPos pos, @Nullable Holder<Biome> biome, 
        CallbackInfoReturnable<WeightedList<MobSpawnSettings.SpawnerData>> cir) {
    
    if (mobCategory == MobCategory.AMBIENT) {
        WeightedList<MobSpawnSettings.SpawnerData> original = cir.getReturnValue();
        if (original != null && !original.isEmpty()) {
            // Check if Bat exists in original spawn list
            boolean hasBat = original.unwrap().stream().anyMatch(item -> item.value().type() == EntityTypes.BAT);
            if (hasBat) {
                int customWeight = DynamicGameRuleManager.getInt(level, BetterBatsFabric.BAT_SPAWN_WEIGHT);
                List<Weighted<MobSpawnSettings.SpawnerData>> newList = new ArrayList<>();
                for (Weighted<MobSpawnSettings.SpawnerData> item : original.unwrap()) {
                    if (item.value().type() == EntityTypes.BAT) {
                        if (customWeight > 0) {
                            newList.add(new Weighted<>(item.value(), customWeight));
                        }
                    } else {
                        newList.add(item);
                    }
                }
                cir.setReturnValue(WeightedList.of(newList));
            }
        }
    }
}

• Disabling Spawning: Setting /gamerule better-bats:bat_spawn_weight 0 completely strips bats from the AMBIENT spawn weight list, preventing any new natural bat spawning.

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🌌 Surface Night Spawning Rules

Vanilla bats only spawn deep underground below specific Y-levels. Better Bats updates Bat.checkBatSpawnRules() via mixin to allow bats to naturally spawn outdoors on the surface at night:

@Inject(method = "checkBatSpawnRules", at = @At("HEAD"), cancellable = true)
private static void betterbats$onCheckBatSpawnRules(
        EntityType<Bat> type, LevelAccessor level, EntitySpawnReason spawnReason, 
        BlockPos pos, RandomSource random, CallbackInfoReturnable<Boolean> cir) {
    
    boolean isSurface = pos.getY() >= level.getHeightmapPos(Heightmap.Types.WORLD_SURFACE, pos).getY();
    if (isSurface) {
        int skyLight = level.getBrightness(LightLayer.SKY, pos);
        if (skyLight <= 7 && level.getBlockState(pos.below()).is(BlockTags.BATS_SPAWNABLE_ON)) {
            cir.setReturnValue(Mob.checkMobSpawnRules(type, level, spawnReason, pos, random));
        } else {
            cir.setReturnValue(false);
        }
    }
}

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🔗 Related Pages

• Bat Ecology, Photophobia & Daytime Roosting
• Dynamic GameRules Reference Table
• Mixin Reference & Injection Hooks