The Canon of Procedural Games

Summary:

Should games which feature adaptive difficulty be considered procedural?

The Canon of Procedural Games

andrewdoull 17 Oct 2009 01:24

While updating the PCG wiki today, I've come across the difficult notion of canon in procedural content generated games. I've flirted with this concept before, by defining games which are prototypically procedural, but in general I've tried to be inclusive rather than exclusive when it comes to including games in the PCG wiki.

I've hit a stumbling point writing up an article on adaptive difficulty - always a controversial point in games. I'll quote the whole article to saving you having to go to the original link:

Adaptive difficulty is the process of adjusting the game in reaction to the player. By spawning new enemies or powering up existing enemies if the player is progressing quickly through the game, or by decreasing the frequency and/or difficulty of existing enemies if the player appears to be having problems progressing, adaptive difficulty techniques attempt to create the 'optimal' game experience.

Classically, adaptive difficulty has been seen as a hard problem, requiring a level of artificial intelligence in the game to attempt to model the player to attempt to determine if they are finding the game easy or difficult.

However simpler RPG style mechanisms can also be seen as adaptive difficulty techniques. Allowing the player to level up by playing through additional easier content can ensure the player is able to grind their way through parts of the game in order to decrease the difficulty of sections of the game where the difficulty level increases. Paradoxically, adaptive difficulty techniques which increase the difficulty of the game by scaling up enemy strength have been fiercely resisted by RPG players, as can be seen by the negative reactions to the difficulty scaling in Oblivion.

Adaptive difficulty is not usually seen as a procedural content generation technique, but it has most of the features of such techniques. It could be seen as decreasing a game's randomness instead of increasing it which would make games which feature it without other PCG features to fall outside the 'canon' of PCG games.

Should I include games which have adaptive difficulty in the PCG wiki? There are plenty of examples of games which have adaptive difficulty and are procedural (Oblivion I've already mentioned, Left4Dead) but there are plenty of games which are not (SiN: Episodes). And I don't want to include every RPG, based on the argument I've made above.

The real question is not whether I should include these games, and the answer to that is probably not, but why? What good reason can I give to not include SiN: Episodes, for instance, as a procedural game?

Again, the randomness argument is the most plausible, but it is not completely convincing.

Convince me.

Last edited on 17 Oct 2009 01:26 by andrewdoull Show more

Re: The Canon of Procedural Games

Makiyivka 18 Oct 2009 07:49

The following is mostly a mixture of typing as I think and thinking at 3am, so hopefully it comes out coherent and useful.

From the 'What PCG is' page, you have created this as your base definition of PCG:
"Procedural content generation (PCG) is the programmatic generation of game content using a random or pseudo-random process that results in an unpredictable range of possible game play spaces."

A potential problem with adaptive difficulty as a PCG technique is that rather than allowing the player to explore an 'unpredictable range of possible game play spaces,' the goal of adaptive difficulty (as I understand it) is to constrain the player into the game designer's preferred play space. That is, if you are too good at the game, the game will get harder, so that you progress as expected. The same is true of the 'too bad at the game' case.

Take Resident Evil 4, for instance. Much of the tension, the overall 'experience,' in the game comes from managing a small amount of resources, primarily ammunition. Therefore, if I, as the game designer, want to ensure that a certain scene or boss 'feels' right, I need to make sure that the player has a given amount of ammunition when entering the fight, so that they get the experience I designed for them. By adding adaptive difficulty, I introduce a nice negative-feedback loop which prevents players from straying too far from this 'optimal' play space, by either removing excess resources if the player is too good (and thus has an abundance of ammo) or by adding in resources if the player is too bad (and is running the risk of leaving the game out of frustration).

Next look at Oblivion. The adaptive difficulty in this game, as far as I understand it, scales the monsters' levels with that of the player. So if I approach a tower at level 1, I will fight a level appropriate enemy. Similarly, if I approach that same tower twenty levels later, the enemies will have leveled up appropriately (perhaps the bandits have full plate mail and magical swords instead of cheap daggers and torn clothing). Now, again, this adaptive difficulty serves to focus the game into a very comfortable and safe player space…I will always be able to vanquish my enemies, provided I put in approximately the same amount of effort as I did previously. This adaptive difficulty removes the player's ability to explore the more 'dangerous' parts of the play space in favour of keeping the game friendly and playable. Now, this may have benefits for many players (I personally disliked the leveling world), but as far as resulting in the exploration of an "unpredictable range of possible game play spaces,' Adaptive Difficulty, as I have seen it implemented, seems to be designed to do the exact opposite: to allow the designer to better control the player experience.

On the topic of Left 4 Dead, could you point me to a description of its adaptive difficulty, if you happen to have one? Because my limited experience with the game seems to suggest that what the AI Director is more an example of Algorithmic Difficulty, rather than adaptive….if I try to play a campaign on a difficulty that is too high for me, I will just fail the campaign. Likewise if I play on a difficulty that is too easy, I will run through it unchallenged. The AI Director may place the zombies in new locations each time, or order in zombie waves in different locations, but if I opt to play a hard campaign, then the AI Director will algorithmically give me a hard campaign.

Anyway, I hope I've at least provided a decent springboard off of which to continue thinking about the issue of adaptive difficulty as it relates to this wiki.

Re: The Canon of Procedural Games

andrewdoull 18 Oct 2009 10:15

On the topic of Left 4 Dead, could you point me to a description of its adaptive difficulty, if you happen to have one? Because my limited experience with the game seems to suggest that what the AI Director is more an example of Algorithmic Difficulty, rather than adaptive….if I try to play a campaign on a difficulty that is too high for me, I will just fail the campaign. Likewise if I play on a difficulty that is too easy, I will run through it unchallenged. The AI Director may place the zombies in new locations each time, or order in zombie waves in different locations, but if I opt to play a hard campaign, then the AI Director will algorithmically give me a hard campaign.

A lot of the press about Left4Dead mentioned it's adaptive difficulty - [http://www.edge-online.com/blogs/gabe-newell-writes-edge] is probably the easiest example to find. I'll add it to the article.

Re: The Canon of Procedural Games

ejh 20 Oct 2009 13:55

Its a tough call on this. Many popular games do some form of adaptive difficulty in ad-hoc and very game-specific ways. Makiyivka above makes a great point: the goal of procedural content is to open the gamespace, whereas often the goal of adaptive AI is to close it (but not always, consider something like the adaptive AI characters in Facade?).

I'd surely consider AI content though, the difficulty and complexity of which certainly affects the enjoyability of the game. I'd say only include games that feature adaptive AI as a major feature, like Left4Dead.

Re: The Canon of Procedural Games

andrewdoull 27 Oct 2009 06:08

Thanks for the responses on this. I'm still not convinced either way, and have had people argue for both sides of the equation. I suspect the best approach to take is to be inclusive, but highlight the fact some people may not consider adaptive difficulty to be classically procedural.