Code structure

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 project: 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.

State of game

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.

Client

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.

Primitive controls

VCMI provides a set of controls a window can be build from. We have already written basic counterparts of most of standard controls like buttons, labels etc. Here is a list of them:

• AdventureMapButton - standard button class for general use (its name is after its first application). Optimized for buttons having standard .DEF graphics. When it's pressed, all functions from its callback field are called.
• CHighlightableButton - basically a checkbox. Has two callbacks: one for selecting and one for deselecting. It inherits from AdventureMapButton because most of graphics handling is common/
• CHighlightableButtonsGroup - a radio button group. It consist of many CHighlightableButtons. Functions from onChange are called when selection is changed (the parameter is the ID of selected button).
• CSlider - a typical slider.
• CLabel - a label with custom font and color. It does nothing interesting.
• CPicture - any bitmap.
• CTextInput - a textbox.
• CGStatusBar - a statusbar for general use.

Adventure map interface

TBD

Town interface

TBD

Battle

Animations of creatures

All animations of creatures in a battle are handled by storing currently displayed animations in pendingAnims vector. When server tells that an event requiring animation happens, info about it is added to pendingAnims. Every animation needs to be initialized (what indicates that this animation has started). show() function tries to initialize all not initialized animations every frame until it succeeds. Then nextFrame call-ins are called until animation removes itself from pendingAnims. During initialization it is checked if this animation can be played now or we must wait.

Showing sequence of stacks, obstacles and wall pieces

Firstly, all dead stacks are printed on the screen. Then alive stacks, obstacles and wall pieces are printed in order of appearance (number of hex they are placed on). This algorithm works fairly well if no creatures move, but due to the fact that while a creature is moving, its position is the destination, not the hex they are walking on, sometimes it makes some graphical glitches that are not easy to fix.

Desynchronization of state of the game and displayed animations

This problem is not limited to battles but here it is the most problematic. GameState is updated immediately after getting info from server while the player should see smooth transition between initial and final states, e.g. when one creature stack attack another one we should see decreased amount of creatures after the animation of attack is displayed, despite the fact that gameState contains the new amount before any animation is displayed. Sometimes it can even lead to crashes when an action of the user makes the battle finished in gameState but wants to see all remaining actions of stacks - but the engine cannot respond to new inquires and destroys all data about stacks that weren't duplicated by battle interface.

This issue can be partly resolved by stopping the processing of data from server but it's not widely used nor elegant solution.

Server

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

Lib

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.

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

Artificial Intelligence (AI)

GeniusAI

TBD