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The code of VCMI is divided into several main parts: client, server, lib and AIs, each one in a separate binary file.

The big picture

VCMI contains three core projects: VCMI_lib (dll / so), VCMI_client (executable) and VCMI_server (executable). Server handles all game mechanics and events. Client presents game state and events to player and collects input from him.

During the game, we have one (and only one) server and one or more (one for each player computer) clients.

Important: State of the game and its mechanics are synchronized between clients and server. All changes to the game state or mechanics must be done by server which will send appropriate notices to clients.

Game state

It's basically CGameState class object and everything that's accessible from it: map (with objects), player statuses, game options, etc.

Bonus system

One of the more important pieces of VCMI is the bonus system. It's described in a separate article.


Most of VCMI configuration files uses Json format and located in "config" directory

Json parser and writer


Main purposes of client

Client is responsible for: - displaying state of game to human player - capturing player's actions and sending requests to server - displaying changes in state of game indicated by server

Rendering of graphics

Rendering of graphics relies heavily on SDL. Currently we do not have any wrapper for SDL internal structures and most of rendering is about blitting surfaces using SDL_BlitSurface. We have a few function that make rendering easier or make specific parts of rendering (like printing text). They are places in client/SDL_Extensions and client/SDL_Framerate (the second one contains code responsible for keeping appropriate framerate, it should work more smart than just SDL_Delay(miliseconds)). In rendering, Interface object system is quite helpful. Its base is CIntObject class that is basically a base class for our library of GUI components and other objects.


Main purposes of server

Server is responsible for:

  • maintaining state of the game
  • handling requests from all clients participating in game
  • informing all clients about changes in state of the game that are visible to them


Main purposes of lib

VCMI_Lib is a library that contains code common to server and client, so we avoid it's duplication. Important: the library code is common for client and server and used by them, but the library instance (in opposition to the library as file) is not shared by them! Both client and server create their own "copies" of lib with all its class instances.

iOS platform pioneered single process build, where server is a static library and not a dedicated executable. For that to work, the lib had to be wrapped into special namespace that is defined by client and server targets on iOS, so that single process is able to contain 2 versions of the library. To make it more convenient, a few macros were introduced that can be found in Global.h. The most important ones are VCMI_LIB_NAMESPACE_BEGIN and VCMI_LIB_NAMESPACE_END which must be used anywhere a symbol from the lib is needed, otherwise building iOS (or any other platform that would use single process approach) fails.

Lib contains code responsible for:

  • handling most of Heroes III files (.lod, .txt setting files)
  • storing information common to server and client like state of the game
  • managing armies, buildings, artifacts, spells, bonuses and other game objects
  • handling general game mechanics and related actions (only adventure map objects; it's an unwanted remnant of past development - all game mechanics should be handled by the server)
  • networking and serialization


The serialization framework can serialize basic types, several standard containers among smart pointers and custom objects. Its design is based on the boost serialization libraries. In addition to the basic functionality it provides light-weight transfer of CGObjectInstance objects by sending only the index/id.

Serialization page for all the details.

Wrapped namespace examples

Inside the lib

Both header and implementation of a new class inside the lib should have the following structure:


Headers outside the lib

Forward declarations of the lib in headers of other parts of the project need to be wrapped in the macros:

<lib forward declarations>
<other forward declarations>

New project part

If you're creating new project part, place VCMI_LIB_USING_NAMESPACE in its StdInc.h to be able to use lib classes without explicit namespace in implementation files. Example:

Artificial Intelligence


Stupid AI is recent and used battle AI.

Adventure AI

VCAI module is currently developed agent-based system driven by goals and heroes.

Programming challenge

Fuzzy logic

VCMI includes FuzzyLite library to make use of fuzzy rule-based algorithms. They are useful to handle uncertanity and resemble human behaviour who takes decisions based on rough observations. FuzzyLite is linked as separate static library in AI/FuzzyLite.lib file.




ERM parser