Command & Conquer 3 Tiberium Wars Designer Diary #6 - Crafting Challenging Opponents
Lead designer Jason Bender explains the process of creating challenging artificial intelligence in this real-time strategy sequel for the PC and the Xbox 360.
The early days of real-time strategy games began with collecting resources quickly to build up a base of operations and devastating armies to destroy your enemies. One of the early pioneers of this type of game was the Command & Conquer sci-fi strategy series, which is set to make its triumphant return on the PC (and its debut on the Xbox 360 console) later this month. In this final designer diary, lead designer Jason Bender discusses what goes into creating a smart and enjoyable foe using artificial intelligence.
Creating a Challenging Opponent
By Jason Bender
Lead Designer, EA LA
When we started working on Command & Conquer 3 Tiberium Wars, we knew that the game would draw different types of players. Some people would be looking forward to classic C&C single-player campaigns, including cool missions, a rich story with full-motion video cutscenes, and familiar units like the orca and the stealth tank. Others would be in it for the multiplayer experience, with fast and brutal unit interactions, lots of micromanagement, and a wide variety of tactical options. Command & Conquer 3 was designed for both breeds of player: You'll find 38 missions in three campaigns, a great mix of classic and new units and structures, a deep story, and a fast, fluid multiplayer game with three balanced sides and a great deal of strategic depth.
That said, one feature that all players will enjoy is the game's artificial intelligence. The AI is used in single-player, skirmish, and multiplayer in several different roles. Certain campaign missions utilize the AI to control enemy forces, particularly in larger battles. In multiplayer the AI can be added to bolster a team when there aren't enough players handy, or as a tough enemy in "comp stomp," where multiple humans battle one or more AI opponents. Of course, in single-player skirmish mode, a single human can play with up to seven AI players as a mix of allies or enemies.
The AI accommodates different play styles through customization. Simply select an AI personality that matches your style of play and you're good to go. Or, have the AI randomly select a style of play and see what strategies get served up. Customizable AI solves the age-old dilemma of past RTS games, where people with different styles of play got frustrated by the uniform tactics of the AI. A player who likes to turtle will be constantly frustrated by a fast AI rush--and vice versa. In Command & Conquer 3, you can let the computer go with what it thinks is the very best strategy, or you can give it a predisposition to use certain tactics and strategies.
In addition to customizable styles of play, the AI also has several difficulty levels. The easy AI exists as a training tool for new players and a nice place to learn the rules of the game. This is crucial for us, as Command & Conquer 3 is built to be totally accessible to players new to the genre. Medium difficulty is designed to offer some pressure and broad use of all available tools, but still give less experienced players some room to breathe. The AI will increase or decrease difficulty slightly to match the player's ability during a battle, so the medium setting in particular can offer a good match for any player between easy and hard skill levels. Hard difficulty is the most difficult AI we could possibly create without cheating. We took special care to take advantage of the places that the AI has advantages over human players, such as unlimited micromanagement and perfect tracking of resources. This allows the AI to make up for a lack of human ingenuity, something that becomes especially crucial in the online world as tactics evolve over time. To satisfy the needs of the top-notch players we also developed an AI difficulty level we call "brutal." This is our hard AI with a cash bonus, which exists not only as a fun challenge, but also a training tool for players who want to spar in preparation for online matches. The idea is that when you are unable of unwilling to play against a top-notch human opponent you can sharpen your claws against brutal AI, thus preparing yourself for ranked matches.
The broad use of the AI in the campaign, multiplayer, and skirmish called for a robust and diverse AI system. We brought back Andrew Garret, a member of the AI engineering crew on Battle for Middle-earth II (BFME2), to bring his AI engineering experience forward into our brand-new AI. He was joined by Will Hutchinson, another engineer of BFME2 fame, and together they set out creating an incredibly robust AI system. Mod makers will immediately recognize that our new AI exists in a highly tunable structure, with easy access to most systems via XML. This is a significant diversion from some of our past AI efforts, which involved heavy world-builder scripting and less versatility for modding.
Once our AI engineers began establishing a strong framework and foundation (a process that took many months), it was time to bring in a gameplay expert to make sure that the AI could really do some damage to highly skilled players but still be fun for everyone to play. For this task we brought in Gavin Simon. Gavin, officially a new addition to our design staff, has actually been with our team since Red Alert 2. He's been a huge C&C fan from the beginning, and he helped test Red Alert 2 while he was still in high school. Gavin took on the task of creating smart tactics, thus imparting his tactical expertise upon the AI. Gavin is the best player on the team by far, and was the ideal expert to "train" the AI.
Together, the AI team created a wide range of tactics for the AI to employ, depending on the circumstances. There are special operations for building base defenses, aircraft, using powers, beefing up the economy, running attacks, and anything else that might need to be done. Each unit type has a priority associated with it, so that the AI will prefer to build some units over others. These priorities also shift depending on what the opponent possesses, so that the correct counterunits can be produced quickly. These operations can all be tuned individually, or even disabled, so that single-player missions and modders can have total flexibility.
The various AI personalities take advantage of these tunable attributes to simulate a variety of play styles typical of human players. The balanced personality runs as efficiently as possible, and utilizes the broadest range of tactics. "Turtle" personality allocates more resources to defense, and holds back a big force for a late attack. "Rush" personality builds small groups from the moment the game starts, with multiple-unit production structures pumping out infantry and vehicles. (Incidentally, rush personality also plays a mean guitar.) "Steamroller" personality concentrates on building huge masses of forces and sending out overwhelming attacks. "Guerilla" emphasizes flanking attacks, finesse units, hit-and-run tactics, and stealth to keep the opponent off balance--a natural fit for Nod. Lastly, any of these personalities can be combined with different difficulty settings, team combinations, and handicaps to create a very broad variety of gameplay experiences.
We also threw in a little secret that might come in handy when you have an AI ally. If you drop a beacon on the battlefield, all AI allies will automatically assemble a team and send them to attack the area near the beacon. This will allow you to call for help from your robo-buddies when you really need it. You can drop additional beacons to move them along if you need help later.
There you have it--a versatile, robust, clever AI for your tactical pleasure. Once you get your hands on Command & Conquer 3, be sure to try a skirmish game and put the AI to the test yourself. Whether you're a beginner or a pro, there's something there for you.
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