Gameplay

Jehee Lee

Seoul National University

What is gameplay?

• The strategies required to reach specific endpoints (in game theory)

• Gameplay is important, but not everything– Choice of car in GTA is not always about payoff, but

about what is fun

• Sometimes, it doesn’t have gameplay– Describe SimCity as a toy than a game– Flight simulator, simulation war games

Gameplay Example

• Adventure game: knight, priest, dwarf, thief• Priest cast spells

– E-bolt (do damage)– Band-aids (heal equal to the damage of E-bolt)

• Which to cast?– Against single opponent– Against opponent using several weapons– Against a horde of opponents with individually weak

attacks

• Choice is rather obvious

Gameplay Example

• Suppose– Band-Aids affect a single target– E-bolts are area-effect spells (damage all enemies in

a give radius)– E-bolts do less damage, but armor doesn’t make a

difference

• Now, which to cast?– Answer is not as easy

Implementing Gameplay

• “A game is a series of interesting choices”

• Choices must be non-trivial, with upside and downside– If only upside, AI should take care of it– If only downside, never be used

• Interesting choices– Payoff depends on multiple factors– Strategy (a series of choices) is required

Implementing Gameplay

• Well-designed game must display complexity

• This doesn’t mean the rules must be complex– Don’t make too many rules– Don’t make the rules too complicated– Emergence from interaction of simple rules

Dominant Strategy Problem

• Articles with “10 killer tactics” or “ultimate weapon”– Taking advantage of flaws in the game design

• Dominated strategy– An option that is never worth using

• Dominant strategy– An option that is so good, it’s never worth doing

anything else

• A dominated option is worthless, and a dominant option makes all the other options worthless

Near-Dominance

• Worth looking for near dominance– Near-dominated - useful in very narrow circumstances– Near-dominant - used most of the time

• Ex) a stun gun is worth using against raptors, but has no effect on other foes– Did I want the stun gun to be a more common feature?

Is the one-off use a positive feature– If the stun gun is going to be used only once, is it worth

spending time on it

Avoiding Trivial Choices

• Transitive combat relationship– Warrior → Barbarian → Archer

• Intransitive relationship– Warrior → Barbarian → Archer → Warrior – Like Paper-Scissors-Stone

• How much better?– (Absolute superiority) Single warrior can beat any

number of barbarians– (Maginal superiority) Single warrior barely beat an

archer

• The superiority should depend on the situation

Environment + Rules = Gameplay

• Classic theory of early medieval warfare– Heavily-armed infantry lacked the mobility– Archers attack and run away– Shooting uphill, archer volleys less effective– Cavalry can easily defeat moving infantry, but cavalry

charging is less effective on a solid line of infantry

• Ex)The Battle of Hastings in 1066 AD– King Harold of England vs Duke Williams of Normandy– Infantry vs Archers+Cavalry– Started on Senlac Hill

Ensuring Interesting Choices

• Ex) Elite in the early ‘80s– Accumulate credits by trading between planets– Earned 1000 credits, replace pulse laser with more powerful

beam laser for 600 credits– Why do we need to wait until we earn 1000 credits (instead of

600 credits)

• The kinds of choices– Should sometimes be taken, and sometimes not depending on

other factors– Timing is critical and depends on the context– Little difference whether take it or not– Always worth taking– Never worth taking at any point in the game

A Toolbox of Interesting Choices

• Strategic versus Tactical• Supporting Investments• Versatility• Compensating Factors• Impermanence• Shadow Costs• Synergies

Strategic versus Tactical

• Strategic choices affect course of game over the medium or long term– cf) Tactical choices apply right now– Different choices should lead to different kinds of payoff

• Ex) StarCraft by Blizzard– Should upgrade the range of Marines’ rifles, or– Should upgrade the damage the rifles do, or– Should allow the Marines to fire faster– The decision depends on

• Opponent units (Zealot or Zerglings)• How many marines you have• What the surrounding terrain is like• Whether you have bunkers built• Whether you anticipate an offensive or defensive campaign

Supporting Investments

• Often game has not only primary goal but also secondary goals– Ex) Primary goal is to destroy enemy– Ex) Secondary goal is to build farms for resources

• Some expenditures directly impact primary goal (ex: buying a mercenary), while others indirect (ex: build farm) called supporting investments

• Primary investments operate at one remove– Ex) improve weapons, build extra barracks

• Supporting investments operate at two remove– Ex) Build smithy can then improve weapons– Ex) Research construction lets you build smithy and barracks

Versatility

• Best and worst thing about options– Does most damage, but slowest– Fastest, but defenseless– Best defense, but little damage– Neither best nor worst, but most versatile

• Most options should be best in some way• Versatility is good for unpredictable environment

– Beginners– Flexibility against unpredictable/expert opponents

• Versatility should make up a disadvantage elsewhere

Compensating Factors

• Consider RTS game where all units impeded by some terrain except for flying unit

• Compensate the unique functionality by– Making it slow– Making it weak (easily destroyed)– Giving it low surveillance range– Making it expensive to buy

• The last isn’t good, because it doesn’t oblige the player to use the unit in an interesting way

Impermanence

• Some advantages are long lasting, while some are impermanent

• Can be used for interesting choices– Ex) choice of medium armor for rest of game or

invulnerable for 30 seconds

• Impermanence in number of ways– Can be destroyed by chance or by enemy action– Can be stolen or converted– Can be applied to something you don’t always have– Certain number of uses (six bullets in a magazine)– Last for some time

Shadow Costs

• In every game, continually presented with costs and trade-offs– Cost doesn’t have to mean money or points– Cost can be the things you had to succeed at before

you could get to the options you are facing next– In terms of time, effort, attention and resources

• Some costs are not direct– Related to supporting investments– Ex) In Warrior Kings, hire mercenaries for gold, build

shops and townsmen to trade, tavern to attract the mercenaries to your town

Shadow Costs

• In Age of Empires– food is inexhaustible while wood is finite– 60 wood, 40 food and 40 sec to spawn charioteer– The unit’s shadow cost changes over course of game

• Early on, food and wood expensive. Spawning time is not important

• Mid-game, wood and food are plentiful. The main concern is how quickly pump out new units

• End-game, no wood, units are priceless

• Variability of shadow costs add subtlety to gameplay

Synergies

• Interaction between different elements of player’s strategies

• Positive feedback– Economies of scale: The more of one type, the better– Economies of scope: Advantage of combined arms

(ex: infantry and tanks)

• Negative feedback– Diseconomies of scale: first unit is the most useful,

others less benefit– Diseconomies of scope: (ex: mixed troops go only as

fast as the slowest)

Synergies

• Ideally, all four of synergies should be in play at once

• Tend to make decisions of timing more critical• Many economies of scale and scope

encourages the player who is already winning– Small mistake magnified throughout game– Ex) Chess, monopoly

• Emphasis on diseconomies creates a “catch-up” factor– Tend to last long time

Final word on Gameplay

• Need to make sure choices interact– Ex) not satisfying to win game just by out-optimizing

the opponent on resource production

• Series of choices should interact to form strategy

• Interact with choices of opponent