From Valve Developer Community
Contingency is an upcoming co-op wave defense FPS for the Source engine based in the Half-Life 2 universe. The project is being developed by Agent Red Productions and is currently in a public beta state, with its source code and developer builds all available to the public via subversion (SVN) on its Google Code page.
As a member of an elite rebel fighting force based out of City 17, you and your four comrades have found yourself in a most hopeless situation: an unstoppable horde is approaching, one that cannot be defeated even by the likes of you and your experienced team. Facing insurmountable odds and with no hope of rescue, there's only one thing you can do: hold your ground and face endless waves of enemies in a suicidal yet heroic effort to save as many future victims’ lives as possible.
You will not survive.
The game is divided into a perpetuating series of two distinct parts: combat phases and interim phases. During a combat phase, players face a specified number of enemies (NPCs) of a certain type called a wave. Players have an unlimited amount of time to eradicate this wave, but if a player dies, they will not respawn until the wave is cleared. If the wave is defeated and at least one player remains, an interim phase begins, and for a relatively short period of time, all players are safe from harm and are free to refine their strategy in preparation for the next wave. Afterwards, another combat phase begins, spawning an even more deadly wave of enemies, and so the cycle continues with ever-increasing difficulty until all players have been eliminated.
There are currently four different types of waves: zombie waves, headcrab waves, antlion waves, and Combine waves. Waves are classified by the types of NPCs found in them. For example, during a Combine wave, players can expect Overwatch soldiers, manhacks, city scanners, etc. No two waves of the same type are exactly the same though, so while one zombie wave might feature mostly slow poison zombies, the next one could introduce a massive horde of speedy fast zombies.
As the game progresses, players may encounter boss NPCs (e.g. antlion guard). These enemies are significantly stronger than their counterparts and only spawn during waves along with their respective wave type. In other words, if a player does come face-to-face with an antlion guard, it will only ever be during an antlion wave. While it is possible to play a round of the game without ever encountering a boss NPC, should one spawn, it must be killed in order for the current wave to end and for the game to continue.
Rather than limiting players by forcing them to choose between fixed, predetermined classes, individuals can pick and choose their arsenal. Players can carry one primary weapon, one secondary weapon, one melee weapon, and one type of equipment (e.g. frag grenades, deployable turrets, etc.) at a time. Loadouts can be changed and saved anytime, but are only applied at the start of a combat phase.
Credits & Props
When players kill an enemy, they receive a certain number of credits. During an interim phase, these credits can be used to purchase stationary props which the player can use to temporarily barricade off certain areas, construct a custom base of operations, etc. How much a prop costs depends on properties like its size and breakability, with the largest unbreakable props being the most expensive.
Players are given additional credits for killing tougher enemies (e.g. boss NPCs) and for performing other helpful tasks, like healing teammates with a health kit.
As the game unfolds, players may come across friendly NPCs (e.g. armed City 17 citizens). Should players choose to interact with these NPCs, they will join their cause and be added to players' global support squad. With further interaction, support squad members can be told to move to a particular location and reinforce a position.
Players' health regenerates slowly over time. Additionally, players have the option of equipping a health kit as part of their loadout which can be carried around like a weapon and used to instantly restore the health of either the user or another player to full.
A player's speed is based both on their health (i.e. the lower your health, the slower you will be able to move) and their current loadout, where each weapon has its own weight penalty. Not coincidentally, the heavier weapons are also some of the most powerful ones in the game (e.g. AR2).
Unlimited primary ammo is provided for all clip-based projectile weapons, but players still have to reload when their clip is empty.
Contingency has plenty of its own unique features, but it is also a culmination of ideas based on a multitude of existing maps, mods and games, especially the following:
- The Call of Duty series' "Nazi Zombies" mini-game and Sourceforts: phase and wave systems
- Garry's Mod: prop manipulation as a gameplay dynamic
- Various Half-Life and Half-Life 2 "Kill Box" maps: initial inspiration for a more polished HL2-based wave defense experience
Both Contingency's source code and content (game files) are licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License. By viewing or downloading anything related to Contingency, you are acknowledging you understand the terms of this license and agree to abide by them.