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Posts Tagged ‘Civilization’

Interviews with Soren Johnson about Spore

Sunday, July 27th, 2008


If you are a devotee of the Civilization franchise or if you are interested in where the upcoming game Spore is headed, there were recently two interviews with Soren Johnson.

The first was at 1up.com. The second was at Gamasutra. In both, he talks about how his experiences with (and distinct interests in) strategy and simulation AI translated over to the world of Spore.

GDC 2008: Soren Johnson’s lecture on the Civ 4 AI

Monday, February 25th, 2008

One of the more intruiging lectures of the 2008 GDC was given by Soren Johnson (MobyGames info) ex- of Firaxis and now with Maxis on the “Spore” team. He was talking about how Civ 4 fit in the spectrum of game AI between two extremes… “Good AI” and “Fun AI”. Here’s some selections from my notes on the lecture. (Forgive the seeming lack of lucidity – I was typing like a madman!)

Also, this is a direct link to Soren’s Slides (.zip) on his blog – which is where the images in this post came from (click to enlarge).

“Good” AI (Play to win)
Beat player at their own game
Essentially a human substitute

“Fun” AI (Play to lose)
Algorithms are the content
Focus on the Player’s Experience

For example, Aggro in an MMO is fun AI.

With tanks, healers, DPS (damage per second) there is a formula for handling it… Trivial AI problem to “solve” by the players.
Aggro determines who AI attacks, let enemy attack the tank, you heal the tank… DPS the mob…
Everyone knows how it works… very predictable. Almost become commoditized with agro tools. Blizzard isn’t trying to be clever – they like that it is simple.

The question with AI design is, where are you trying to fit? Across the spectrum.

  • Chess is “good”
  • Starcraft is more towards “good” (no real diplomacy – assumption is that they want to kill you.)
  • Civ IV split the gap. Deep diplomacy but very symmetrical game design.
  • Heroes of Might and Magic is more towards “fun”. Not as focused on the excellence.
  • Desktop tower defense if pure “fun” AI.

Rule sets?
Good side tends towards fixed rule sets. (e.g. Chess)
Fun side tends towards evolving rule sets.

What are the best environments?
Good AI tends towards Multi-player
Fun AI tends towards Single-player

Tactics available to AI?
Good AI will do everything available.
Fun AI will do limited tactics.

Measuring performance?
Good AI has objective measurements
Fun is subjective – e.g. difficulty over performance

Turing test?
Good AI passes
Fun AI… this question is irrelevant.

The question is: “Play to win or Play to lose?”

With Civ IV, the AI does have limited options. There are a lot of options that they do not put on the table for the AI. Esp. with diplomacy. E.g. fighting a war… as a player, you can ask them for stuff if you promsie to quit war, then attack them over again. AI doesn’t do that.

Civ has:

  • Both fixed and evolving design
  • Symmetrical
  • Single Player
  • Limited Options
  • Objective Testing
  • Fails Turing test but it isn’t irrelevant.

Every player is different… some want things like challenge, sandbox, narrative.

For narrative, you want to aim for personality, for the AIs to maintain memory about you. It’s OK for them to fall for traps. They built that into the leaders in Civ 4.

With regard to the challenge, you “want player to win or at least understand WHY they lost.

Need for difficulty levels:
Lets sandbox players off easy
Gives Challenge players a goal
Increases available tactics.

Where does cheating fit?
Completely Good AI does not.
Completely Fun AI n/a There is no concept of cheating (e.g. desktop tower defense)
In the middle… yes?

The Noble level in Civ 4 is the “even level” with regard to production modifiers, etc.

But Noble has other cheats… e.g.

  • Animal/Barbarian combat bonuses
  • No Unit support
  • Better Unit upgrades
  • No Inflation
  • No War Weariness

The AI needs more help in these areas.

For example, AI does not leave cities empty like a human would… so unit support costs. Human army and AI army will never be the same size because they have to keep units in their cities… therefore cut the support costs for the AI since they need to have a larger army.

Cheats should NOT be linear… certain you want to help more or less as you progress your diff. levels.

Cheats should never feel unfair! Examples from past Civs that players hated…

Civ 1, 2
Free wonders
Gang up on human (In Civ 1: If year > 1900 and human in lead, declare war on human)

Civ 3, 4
Human-blind diplomacy (Never checks “is human?”)
Information cheats (they DO have info cheats – most of them come down to limited dev. Resources… e.g. fog of war is very expensive)

Information cheats can really backfire on you. E.g. Amphibious Assault Judo using empty port cities in Civ 3. (solved by determining random time for updating the assault target, ignore temporary data such as nearby units.)

Cheating is relative:
The Tech Trading Problem…

  • AI must trade techs
  • AI must trade fairly
  • Human can sell techs cheaply

Only two of these can be true… So… should AI sell techs cheaply? Solution? Can AI pursue altruism?

When the AIs were trading often, it made for very even technology levels between all players rather than some groups ahead and others lagging. Everyone had everything.

Solution in Civ IV

AI can undersell by 33% but…
Tries to make up difference in gold
Only trades on random turn intervals
Uses same “Refuses Trade With” logic as with human.

Arbitrary rules e.g. “I will never trade Iron Working with you.”

What is the point of cheating?
Are we trying to…

  • Write the “best” AI?
  • Beat the human?
  • Be fair?

Designing for the AI?
Can AI handle the options in the gameplay?
OTOH, make sure not designing just for AI. Legitimate reason for design decision. (e.g. closed borders, enforceable peace treaties)

Traditional testing fails
Automated testing helps greatly
Need hard-core fans to analyze
1.5 year closed beta, peaked at 100 users, bi-weekly patches.

They used soft-coded AI:
No AI scripts
No enums (No “Temple”)
Less brittle code
Less predictable AI is not always a good thing.

Probabilistic Reasoning – Weights to factors, values to situation

Data-driven Mods – AI was stand-alone so that it was compiled into dll. CvGameCoreDLL.dll was 100% independent of engine.

Soren Johnson – “A Farewell to Civ”

Sunday, February 10th, 2008

Soren Johnson, AI guru behind Civ 3 and Civ 4, posted an interesting tidbit on his “Designer Notes” blog entitled “A Farewell to Civ“. He mentioned that since he is no longer with Firaxis (having moved over to the Spore team), his GDC lecture next week will really be his last hurrah in speaking about his work with the Civ series.

One thing’s for sure, I will be avoiding writing about Civ 4 in Post-Play’em until after I attend this lecture. One quote caught my eye:

Essentially, I will be talking about the difference between thinking of the AI as the player’s opponent and thinking of it as simply an extension of the core game design (what one might call the difference between “good” AI and “fun” AI). There will also be a long section on AI cheating – the bane of my existence for many years – concerning which type of cheats are acceptable to players and which type are not, using Civ as an extensive case study. Further, I hope to prove that, for Civ at least, there is no such thing as – and never could be – a “fair” difficulty level where the AI is playing the same game as the human. Your mileage , of course, might vary.

I don’t want to make the mistake of assuming something he did was cheating, or something I thought was cheating was actually brilliant AI work on his part!

Cheating or not, he has done some exceptional work in making Civ 3 and Civ 4 an absolute delight to play… even as an AI guy. I’m looking forward to meeting him.

Look for updates from GDC both here and in the IA News blog.

Sid Meier to receive Lifetime Acheivment Award

Tuesday, January 8th, 2008

Sid Meier, strategy game designer and gaming icon, will be receiving a Lifetime Acheivement Award at this years Game Developers Choice Awards at the Game Developers Conference in San Francisco this February.

According to this announcement at Gamastura.com:

CMP’s 2008 Game Developers Choice Awards, the highest honors in game development acknowledging excellence in game creation, will honor computer strategy game luminary Sid Meier with a Lifetime Achievement Award at this year’s ceremony taking place at the Game Developers Conference (GDC). The Lifetime Achievement Award recognizes the career and achievements of developers such as Meier who have made an indelible impact on the craft of game development, as he has with the creation of a number of genre-defining titles including Civilization and Pirates!

I am currently beating my head against the wall that is Civ 4 at the moment, and got many years of pleasure out of the original Civilization and especially Civ 2. I also remember vividly playing F-15 Strike Eagle in the mid-80s and later F-19 Stealth Fighter. Because of what he has meant in my gaming history, I will be honored to be able to be present for this ceremony. Sid Meier truly is one of the great game designers in the industry and I personally salute him and thank him for his contributions.

Congratulations, Sid! Keep it coming!

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