Hello, I wonder how to spawn a mob in a cave/ under a specific light-level

In your Entity class you need to override this method

    public boolean getCanSpawnHere()
    {
        return this.worldObj.getDifficulty() != EnumDifficulty.PEACEFUL && this.isValidLightLevel() && super.getCanSpawnHere();
    }

 

To add the entity to spawn just loop through all the biomes from BiomeGenBase use

EntityRegistry.addSpawn()

But it can't extend EntityMob

You mean your Entity is a passive entity?

It is if you hit it 'mad' but I just copied the isValidLightLevel from the entitymob class

Will that work

Well as long as the class path extends EntityLiving you should be able to use getCanSpawnHere() and could you show me how you edited it.

protected boolean isValidLightLevel() {
	BlockPos blockpos = new BlockPos(this.posX, this.getEntityBoundingBox().minY, this.posZ);

	if (this.worldObj.getLightFor(EnumSkyBlock.SKY, blockpos) > this.rand.nextInt(32)) {
		return false;
	} else {
		int i = this.worldObj.getLightFromNeighbors(blockpos);

		if (this.worldObj.isThundering()) {
			int j = this.worldObj.getSkylightSubtracted();
			this.worldObj.setSkylightSubtracted(10);
			i = this.worldObj.getLightFromNeighbors(blockpos);
			this.worldObj.setSkylightSubtracted(j);
		}

		return i <= this.rand.nextInt(;
	}
}

@Override
public boolean getCanSpawnHere() {
	return this.worldObj.getDifficulty() != EnumDifficulty.PEACEFUL && this.isValidLightLevel()
			&& super.getCanSpawnHere();
}

What is with

this.rand.nextInt(32)

You should also check to see if the entities pos can see sunlight using

worldObj.canBlockSeeSky(blockPos)

Well, I copied it directly from the EntityMob class so...

Is this OK:

protected boolean isValidLightLevel() {
	BlockPos blockpos = new BlockPos(this.posX, this.getEntityBoundingBox().minY, this.posZ);

	if (this.worldObj.getLightFor(EnumSkyBlock.SKY, blockpos) > 10) {
		return false;
	} else {
		int i = this.worldObj.getLightFromNeighbors(blockpos);

		if (this.worldObj.isThundering()) {
			int j = this.worldObj.getSkylightSubtracted();
			this.worldObj.setSkylightSubtracted(10);
			i = this.worldObj.getLightFromNeighbors(blockpos);
			this.worldObj.setSkylightSubtracted(j);
			this.worldObj.canBlockSeeSky(blockpos);
		}

		return i <= this.rand.nextInt(;
	}
}

@Override
public boolean getCanSpawnHere() {
	return this.worldObj.getDifficulty() != EnumDifficulty.PEACEFUL && this.isValidLightLevel()
			&& super.getCanSpawnHere();
}

?

Well I have no Idea why that piece of code was needed, but I guess it was necessary. But that piece of code only makes it spawn at light levels 8 and lower.

 

Is this OK?

There was no need to change that I think do you want it to spawn at high light levels or low light levels like mobs? If so that was fine, but since you want it to only spawn underground you need to add

worldObj.canBlockSeeSky(blockPos)

to the getCanSpawnHere() method

I have that

Well I have no Idea why that piece of code was needed, but I guess it was necessary. But that piece of code only makes it spawn at light levels 8 and lower.

 

There was no need to change that I think do you want it to spawn at high light levels or low light levels like mobs? If so that was fine.

 

So now I have this:

protected boolean isValidLightLevel() {
	BlockPos blockpos = new BlockPos(this.posX, this.getEntityBoundingBox().minY, this.posZ);

	if (this.worldObj.getLightFor(EnumSkyBlock.SKY, blockpos) > this.rand.nextInt(32)) {
		return false;
	} else {
		int i = this.worldObj.getLightFromNeighbors(blockpos);

		if (this.worldObj.isThundering()) {
			int j = this.worldObj.getSkylightSubtracted();
			this.worldObj.setSkylightSubtracted(10);
			i = this.worldObj.getLightFromNeighbors(blockpos);
			this.worldObj.setSkylightSubtracted(j);
		}

		return i <= this.rand.nextInt(;
	}
}

@Override
public boolean getCanSpawnHere() {
	return this.worldObj.getDifficulty() != EnumDifficulty.PEACEFUL && this.isValidLightLevel()
			&& super.getCanSpawnHere() && this.worldObj.canBlockSeeSky(this.getPosition());
}

Will this work?

That should work, but now you need to add the entity to spawn in all biomes.