The Death of the Level Designer: Procedural Content Generation in Games (Part Six)

(You'll want to read parts one, two , three, four and five first)

The human brain has a powerful set of tools for detecting and matching useful patterns in otherwise chaotic data. This set of tools can be conditioned to override normal behaviour patterns in the presence of sufficiently powerful and randomly provided incentives: so-called operant conditioning. You will have probably seen the term 'Skinner box' associated with certain types of game-play: in particular with MMORPGs and slot machines, where people become addicted to randomly provided rewards for repetitive activity.

But the same set of pattern matching tools are useful for the designer of procedural content generation systems. The semi-randomised output of PCG systems will be picked over by the player's brain, and the underlying systems hopefully understood and enjoyed. This reinforcement of play through randomisation is hopefully a more 'nutritious' game environment that simply statistical delivery of reward and one I would expect Johnathan Blow to commend rather than criticise.

The greatest challenge of procedural content generation will be to augment or replace human intelligence in the creation of meaningful narratives in computer games. But even in a single player game, there is a powerful creative intelligence involved in the decision process, and that is the player themselves. A procedural content generation system may be able to leverage this human intelligence in creating meaning and narrative: in part through relying in part on serendipity, happenstance and superstition. In juxtaposing two disparate game elements, the human mind will attempt to find a meaningful relationship between them, and provided that the game does not mix every game element into a brown stochastic blend, the player will build up a narrative of moderate complexity from very simple components. Such a narrative may be no more complicated than 'first I did this, then I did this, and then I did this', but it will have meaning.

It is possible to go too far in procedural content generation techniques: too far being when no two games have any elements in common. This may still be an interesting game - Minesweeper being a good example - but a less interesting movie. Even Minesweeper has a beginning, a middle, some tough choices where a guess might be required, and an end. Most games will have more complex choices that could be formed into a player-centric narrative. Angband for instance encourages the player to stay within a certain distance of the surface until certain resistances are acquired - encountering monsters deeper in the dungeon without these resistances would likely result in game over. A more sophisticated example of these player-centric narratives is the 'Day in the Life' posts that many games encourage - these can either be mundane or dramatic retelling of in-game events from the perspective of the player controlled avatar.

These player-centric narratives, while interesting, are probably not what you envisioned when you hear 'procedural content generation of narrative'. And while the emergent narratives of Dwarf Fortress are a sophisticated example of what is possible with a sufficiently deep game system, as mentioned, not every game developer has the time, resources and fortune to develop this type of game.

What would an explicit, as opposed to emergent, PCG narrative system look like? One way of implementing this is little more than a sophisticated puzzle generation system - essentially a string of escalating Fed Ex quests, and randomly selected Blankety Blank sentences. This is still developer expensive, and at the same time not particularly rewarding for the player, as the systems underlying the puzzle generation is no more sophisticated than the statistical generation of reward probabilities in Skinner Boxes.

By increasing the complexity of the systems underlying the puzzle generation, there is a greater sense of involvement from the player, who must decode these underlying systems in order to maximise their rewards from successful puzzle solving (or questing, or whatever game equivalent process is). And the easiest way to increase this complexity is to have a behind the scenes meta-game, that the player has no direct involvement in.

Consider the plight of an individual person living in the world of a game of Civilisation IV. They may be pivotal to the outcome of a single battle, if they are in the position of being a spy, or help advance the civilisation, if they are a Great Person. Each civilisation is run by a leader, whose particular traits inspire the civilisation to work better in certain areas. But no individual (except the 'hand of God' player who is playing the civilisation behind the scenes) is responsible for the actual decisions taken from turn to turn, how the civilisation advances and how the game of Civilisation IV is played.

Now, replace all the human players playing a game of Civilisation IV with computer players. And instead put the human players in the roles of individuals living in the game world. Civilisation IV has suddenly become the meta-game. Individuals will perceive the actions of the AIs controlling the game only through their indirect effects: cities will be built, technologies gained, enemies routed and civilisations fall. But no player in the game will directly be able to control these effects - their influence will instead be felt only as warriors or spies, or great people or perhaps civilisation leaders.

The actions of the AIs in controlling the meta-game should appear to the individuals in the game to be a consistent narrative. An AI's decision to amass armies on the border to invade a neighbour will have profound in-game consequences. Whether the invasion is successful or not could be decided by one individual: a spy whose vital information enables the encirclement of enemy forces, a leader who can inspire his troops to break through the enclosure, a peasant who correctly shoed the horse of a general so he wasn't thrown from it's back. But the fact that the attack occurred, and the consequences of it, should form a consistent narrative from the player's point of view because it follows a consistent set of meta-game rules, which the player may be able to decode over the course of the game. With sufficient understanding of these rules, the player may be able to predict which side to take, when to rally his troops, when to flee the scene.

And Civilisation and other 4X games are well understood problems, with sophisticated AI, that can provide a narrative backdrop to a lower level game involving player control at an individual or a squad level. There are already examples of blended RTS/FPS games such as Natural Selection and Savage: The Battle for Newerth that have proven successful using this kind of idea. The weakness of these games, and the reason that the Valve elected not to have a commander class in Team Fortress 2, is that the success of the game depends heavily on the competence of the battlefield commander player. Replacing the battlefield commander with an AI levels the playing field in this regard.

And hopefully makes the story behind the play.

Further Reading:

The articles and links sections on the Procedural Content Generation wiki.
Proceduralism: The follow up article series.