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As WP's senior editor, I edit review and preview articles, attempt to keep up with the frantic pace of Rainier's news posts, and keep our reviewers on deadline, which is akin to herding cats. When I have a moment to myself and don't have my nose in a book, I like to play action/RPG, adventure and platforming games...

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'S.T.A.L.K.E.R: Shadow of Chernobyl' - A.I. Revealed

by Judy on Jan. 19, 2005 @ 8:39 a.m. PST

GSC GameWorld sent out a newsletter with details on how the AI it has implemented in its FPS S.T.A.L.K.E.R: Shadow of Chernobyl will work, react to circumstances, and how the development team faced the necessity to invent new methods of game AI. Read more for the full newsletter...

Honestly and earnestly: AI

Today we would like to raise the curtain over solutions and ideas behind one of the key S.T.A.L.K.E.R. components: the artificial intelligence. What were the thoughts we took the governance of when creating the game world, what urged us to adopt a lengthier, but more interesting a way, and what goals have been reached? The pleaser is here.

Search for new ways to use artificial intelligence

Early in the development of S.T.A.L.K.E.R. game mechanics we faced the necessity to invent new methods of game AI… The thing is, a free world as we see it in the game, should provide for a new approach to characters inhabiting it. As announced previously, our primary ambition was to create a living-and-breathing world. To accomplish that, on all the Zone levels we implemented the system of life simulation, allowing calculating all the processes within the realm of the game… Still though, we’ve been only half-way through as, apart from processes occurring beyond the player’s sphere and thus impacting his events in indirect way only, there is an area of direct contacts of the player and the world’s denizens. So, the second part of enlivening the world involves the events directly related to the protagonist. Through the development, it became clear that the old methods, when characters placed in certain spots awaiting the player only to then react in a practically single possible way – opening fire on the player, would be inapplicable here.

Thus, we concluded it necessary to develop a universal behavioral scheme of life and activity as for NPCs, so as for animals in S.T.A.L.K.E.R. Such a scheme would consider outer conditions, possess a set of reactions and behaviour types for assorted situations.

Now we can say that the system lives and functions. Below is a brief description of the system’s capabilities.

Life and activity of NPCs and monsters

In real life all the living creatures require feed and rest. So as in our world the sense of hunger flogs a creature to seek food, and the acuter is hunger, the more aggressive the monster becomes. After satiation the animal either gets to rest – sleeps therefore, or sets off to inspect his territory. All the character types have their personal territorial preferences. Thus, for instance, rats prefer basements, ruins or dumps, while blind dogs adore roaming down valleys and forests. During the look-out there may be encountered an aggressor – a hostile creature or stalker. Then, depending on circumstances, the creature will decide whether to attack or clear out.

Reaction to circumstances

In the real world a gigantic number of varied conditions defines the choice of a certain reaction for a living creature. In terms of game mechanics, as of now, we see it impossible to implement all of them. We had to seek guidance of the main mechanisms which juxtapose with our game mechanics. Both limitations and conditions impacting NPCs should influence the player in about the same way. So, the mechanism of choice of actions, depending on situation, includes a set of functions, which provide for an adequate assessment of situation serving a choice-making factor for an NPC or monster. Firstly, the attitude towards the creature is determined – it can be friendly, neutral or hostile. Depending on the attitude, the choice of behavior model is made. The friendly attitude determines relaxed behaviour, the neutral one – a wary way, while the hostile attitude urges a combat approachs. Before getting into combat, however, the creature will evaluate the battle advantages – if the battle is to disadvantage, the NPC will disregard or merely avoid facing the opponent. In case the combat is deemed to be of advantage or is unavoidable, then through certain functions the chances against the opponent or a group of opponents are evaluated. Here the enemy type, number, condition, armament, distance to opponent and so on are taken into account. This allows obtaining a realistic picture of creature’s behaviour, where depending on chances of victory and courage, the creature either attacks, or, retreats a hostile company in fear.

The mentioned mechanisms make it possible for NPCs and monsters of S.T.A.L.K.E.R. to amazingly enliven the game, adequately react to the events and survive in the highly aggressive Zone environment.

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