Zen Worlds MMO Middleware - Design Sneak Peak

Lightweight but Industrial Strength

The foundation libraries being used for Zen Worlds are currently being used in mobile and embedded devices, so the core frameworks are extremely lightweight, but the same frameworks and libraries scale to handle thousands of clients utilizing less than a few megabytes of memory and less than 10% of one CPU core.

It's thread safe and multi-core ready, scaling nearly linearly as you add more CPU cores. The more CPU cores you have on your server the faster it performs and the less percentage of your overall CPU horsepower is devoted to networking. Less CPU and memory utilization means more simultaneous clients.

Service Oriented Architecture

Using SOA is a key design decision for anyone wanting to create something that is scalable.

By separating your game components into individual services that handle a single section of your game, you're free to dynamically restructure your physical and logical architecture. This allows automatic load balancing and failover, and provides for easier to maintain code.

For an MMO RPG as an example, you would separate your game components into individual services that each handle one task: Login, NPC Dialogs, Pathfinding, Characters, Trade / Auction, etc.

Data Grid

By organizing all of your data into a data grid, you get significantly higher performance than if your services were directly accessing a database.

The data grid can be organized such that all of the data for a particular subject area or service is located in the same process as the services requiring the highest bandwidth access to the data.

Subsets of the data can be split across multiple nodes, or even redundant nodes so as to provide for hot-standby of your data.

Writes are persisted through a transaction log and then to the database, or directly to your database depending on your needs, and then replicated to other nodes or game clients via a "publish / subscribe" mechanism and cached on the client side.

What's the advantage of this mechanism and the caching? No more DataBlocks! Your game zones, game zone data, meshes, textures and other assets are distributed via a publish / subscribe mechanism, making it so that updates can be pushed to clients immediately, which is fantastic for development and testing and moved over to your production system when you're ready to go gold.

The equivalent of Torque's "data blocks" are cached in a client local database and encrypted containers, making it so that they're only downloaded once, and only downloaded on demand according to your game rules.

Game Engine Agnostic

By creating middleware that doesn't target any specific game engine, developers can choose the game engine client that best suits the needs for their games, yet still benefit from the features provided by Zen Worlds.

We accomplish this feature through the use of frameworks and generic interfaces that abstract the implementation and ties everything together.

All you need is a bit of skill with C++ to integrate the middleware with your game and voila, your game scales to vastly huge numbers, capable of supporting millions of players and thousands of simultaneous players per zone.

Application Server

The heart of the framework is a C++ application server, much like JBoss, WebSphere, and many others that are available in Java and Python.

We chose to write a completely custom application server for performance and integration reasons. Since it's all pure ISO C++, it's cross platform, runs on Linux, Mac OS X and Windows, and easily integrates with your C++ code.

It also integrates with a scripting framework that makes it very easy for you to integrate your own scripting language or use an off the shelf language such as Lua or Python.

Frameworks and Plugins

Every core component is written as a plugin, making it very easy for you to integrate new pieces into your game clients and zone servers.

Just as GG did with TGEA 1.8.x for Audio (FMOD and OpenAL), we've taken this a step further and provide generic frameworks with plugins for physics, databases, A* pathfinding, community services, login / authentication services, etc.

With everything kept in separate compilation units, you only use what you need and don't even bother compiling that which you don't.

Licensing

Most of this is free and open source software, using ZLib so there are no copy-left restrictions. (i.e. you can use it commercially and you don't have to redistribute your source code.)

Some of this will be distributed as closed source as an MMORPG starter kit. Although the pricing is still yet to be determined, it will definitely carry an "Indie friendly" price tag.

Status and Roadmap

Much of this is complete and downloadable. The C++ application server, the networking, the plugin system, and all of the plugins mentioned are currently being beta tested. The lastest version of the source code is available for downloading on Sourceforge.net.

We will begin closed beta testing of the MMO frameworks in the next two months.

If you are interested in helping with a community project that integrates this framework with TGEA 1.8 (and/or possibly T3D in the future), please let me know. We will only be integrating the free open source portions, so anything that results from this will be free for the community to use.

And now for the obligatory image:

Arcanoria is one of the games being used to beta test Zen Worlds. I really like this screenshot even though the lighting is off a bit because it shows off his dynamic skies and fully dynamic water. (yes, the waves actually move!)

Zen Development Blogs:

Zen and the Art of Indie Game Development