21w37a Block Entities change and what it means for API.

Hi, so basically this is to explore some of the changes in 21w37a to block entities and what it could lead to for the API.

Serialization changed quite a bit, the writeNbt method now returns void and is protected, other public methods should be used, one is basically a proxy, another one adds the id key with the BE type identifier, and another one adds in addition to the id key the x, y, and z fields.

But that’s not the most important changes, the most important change is toUpdatePacket, the return type changed to Packet<?> and the BlockEntityUpdateS2CPacket changed a lot since now it takes a BlockEntityType parameter (got unhardcoded a lot).

All of these changes basically makes BlockEntityClientSerializable obselete. I would recommend:

• make BlockEntityClientSerializable deprecated, implementation-wise remove the “hack” to the packet.
• in docs: tell mods to use the BlockEntityUpdateS2CPacket, it has a function to create an instance from the BE.
• offer the sync method as a helper method outside of BlockEntityClientSerializable

[LambdAurora]

Haven’t seen it that it was removed, nice.

I have to say that ((ServerWorld) world).getChunkManager().markForUpdate(pos); is definitely not intuitive.

[Pinaz993]

For all who were as lost as I was when attempting to make a block entity sync to the client: I would like to share what I did that worked.

For a while, I was only able to make the data sync when the BlockState changed. (This was after implementing toUpdatePacket()) That changed when I added ((ServerWorld) world).getChunkManager().markForUpdate(pos); to markDirty(). This marks the block position as one that has a block entity to be synced with the client soon, usually within a tick.

However, this will NOT sync your block entity data when the chunk loads. For that, you must turn to toInitialChunkDataNbt() I mistakenly thought that this was data to be sent when the block is first initialized, as in when a new one is placed. (Don’t ask me how I made that mistake. I haven’t a clue.) This is data to be sent when the chunk is loaded. This happens either when the server is loading the chunk into memory from saved data, or when the client is requesting a chunk that is already loaded into memory.

As a bonus, (and as mentioned above), once you implement toInitialChunkDataNbt(), you can simplify toUpdatePacket() to the following:

    @Nullable
    @Override
    public Packet<ClientPlayPacketListener> toUpdatePacket() {
        return BlockEntityUpdateS2CPacket.create(this);
    }

Thus if you do updateListeners() or markForUpdate() when some changed data needs to be sent to the client, and implement both toUpdatePacket() and toInitialChunkDataNbt(), your block entity’s data shouldn’t desync from the client.

(Edited to remove reference to updateListeners(), as that is for when the VoxelShape changes and pathfinding entities need to be updated as to that fact. That’s expensive, and in fact was the very reason BlockEntityClientSyncable existed in the first place.)