Game Design and Artificial Intelligence - Bournemouth University

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Game Design and Artificial Intelligence David Hopkins Fig 2.2 – The layout for the crew AI working state. “ Because game character behaviour can be modeled (in most cases) as a sequence of different character “ mental states” – where change in state is driven by the actions of the player or other characters, or possibly some features of the game world – game programmers often find that finitestate machines are a natural choice for defining character AI.” – p284 AI wisdom [Houlette00] For the Crew AI, there are two FSMs. One that isn't fully implemented in the game which is the basic FSM for working state (see fig 2.2), the second is the emotion state machine. The working FSM is designed to find out whether an NPC is working on a job (eg. Gunning, piloting etc.) or is idle due to refusing orders or finishing a current one or if it is moving to a new location based on a new order. The emotion state machine works slightly differently but uses the same theories. Artificial Emotion. As previously mentioned in the design, the artificial emotion is a method for the NPCs to judge the player through the decisions made based on his statistics. Each NPC carries an OPINION statistic on each character in the crew, including the player. This counter, between 0 and 100, changes as the game progresses based on the input from the player and events happening through the ship. The emotion state machine then uses this counter as part of the calculations to figure if there any changes in emotional states. The class for the AI is defined below: class crewAI : public crewMember { public: std::string getType(void); int state; int emotion_state; int wages;//WAGES is 14, 1 being minimum, 4 being max int aggression;// use this to judge orders. int discipline;// and this! bool refuse_order; int ORDER; double OPINION_player; double OPINION_crewAI; Page 14 of 22
Game Design and Artificial Intelligence David Hopkins double HAPPINESS_general; double HAPPINESS_daily; double FSM_TIMER; int FSM(); int emote_FSM(); void update(double); }; crewAI(int); ~crewAI(); The key to the NPC’s judgm ent is based on the aggression value in the demo game, although ideally more statistics would be considered. Both the pilot and gunner can be given the commands based on their aggression, and both have their preferred aggression factors. If the gunner is an aggressive character, he will not appreciate being told to fire slowly and accurately. If this occurs during the game, the NPC’s OPINION_player will decrease by one. This is only a minimal amount, but if the player continuously issues this order the NPC will become more likely to refuse new orders and will switch to doing what he would rather do. However, good performance will counter this, every time experienced is gained, the OPINION_player will be increased based on the amount. The emotion state FSM often uses the OPINION_player to help with calculations to see if the state needs to be changed. Every five seconds the function will be called: If(refusing_order false) Test if orders to be refused(); If(refusing_order true) Test if Opinion has increased; Test if orders to be refused(); If true, refusing_order false; If(state is normal) { if(FEAR function() returns true) return new_state; if(LUCK function() returns true} return new_state; } If(state is not normal) Check to see if state returns to normal; The above pseudo code will find out what emotion_state the NPC is in and if it is taking new orders. The program uses this information elsewhere in the program to change the NPCs attributes if needed Page 15 of 22
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Game Design and Artificial Intelligence - Bournemouth University

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