Question: What stops BTW from being SMP compatible?

[empath]

This isn't a request to make it compatible, I'm just curious as to what the technical reasons are for it not working with SMP and what needs to be done to make it work?

[Katalliaan]

It's to do with the differences in the coding of each. The new items, their behavior, their crafting recipes and the changes made (getting hemp, wolves producing dung) would all have to be added to the server. I'm sure I'm missing something, and I'm sure that someone more knowledgeable about modding will fill in the missing information.

[finite8]

I haven't looked into it, but if you examine the Client code, there is a critical element in most Entities and Blocks where it basically checks to see if it is in Multiplayer mode and if it is, it returns (stops processing the method).

I think you will find that there is a lot of messiness to do with the way MC works in Multiplayer mode vs Singleplayer mode. There was a big hoo-hah just trying to get Server-Side inventory working. From what i can tell, alot of games that have both an Online and Offline mode function in the same way in both modes. When playing single player mode, the World is hosted on the players machine and then you interact directly with that world. You effectively host your own game and connect to it, just wihtout making an actual TCP/IP connection. If done this way, then it is easy to switch to Multiplayer mode because you just point your client to a TCP/IP address rather than the local instance.

Minecraft seems to have 2 very distinct differences in the way it works. A lot of client side functionality has to be disabled and replaced with the Multiplayer logic in order to get things working. i.e: A mobs AI needs to be handled Server side, not client side. I haven't looked at the Server code yet but i am somewhat terrified at what I will find.

[Miss_Kat]

Notch said sometime ago that with the 1.8 update, the code for SMP and SSP would be integrated into each other somehow? No one knows what he's going to do, exactly, and Flowerchild wants to wait to see what happens before attempting SMP. It doesn't make a lot of sense to go to all the work to make the mod SMP compatible only to have it all go to shit with the update.

[Battlecat]

As I understand things, currently to get a mod like better than wolves working on a server, every player on the server would first have to install the single player version of the mod on their client. There would have to be an additional server specific version of the mod that would handle transmitting the actions of each new block from client to client so all the clients see the same behaviors from the machines.

I'm sure there's other bits, but it's a very complex undertaking, especially since 1.8 or 1.9 (I've heard both cited) will make major changes to the way SMP and SSP integrate, which should theoretically make it much easier to develop an SMP mod in the style of better than wolves. As I understand it, it's not that it can't be done now, it's just that technically it's very complex and the future changes may make it easier, and certain the architecture changes are going to have a major impact on existing mods anyhow.

[FlowerChild]

Honestly, I don't think Notch has stated which version the merger between the server and client code would take place in. He just said he'd be working on it sometime in the near future, and I think people have assumed that to mean 1.8 or 1.9.

[Battlecat]

Thats true Flowerchild. I think the only definitive statement on the subject from notch is that it is one of the last jobs before the final release. More importantly, he has fairly clearly stated that the above mentioned technical changes won't be in 1.8.

Source: Notch's Tumblr Blog, June 27, 2011(see fourth paragraph) Granted, all this information is subject to change.