keep your game in the fun zone - designing an ai director

@swagentrotz Blazing Badger


Who is talking?

Sascha Wagentrotz

CEO, Co-Founder and Game Designer

Blazing Badger GmbH

Founded in April 2014

Based in Frankfurt, Germany


Softography

Keep your game in the fun zone

Designing an AI Director


Why would your game not be fun?

The challenge structure is unstable.

The challenge parts don’t combine the way they are supposed to.



Specific Problems

Spawn camping

Getting one-shot

Button-mashing to victory

Out of ammo/Stuck on low health

Farmed up to invincibility

Difficulty affects enemy damage/health only


Why does this happen?

Challenge flow is static

Spawn timings are pre-determined in most cases

Enemy distribution is pre-defined

Each enemy is allowed to make its own decisions

Enemies don’t take the actions of other enemies into account


Solution: AI / Combat Director

DOES:

Controls all elements of the challenge with perfect knowledge

Enforces specific dynamic

Adjusts on the fly within seconds

Offers many parameters to affect difficulty

DOES NOT:

Make the game easier if you play badly! (if done right)


WTF is an AI Director?

Superordinate Entity that takes control of the “big picture” of your game and features a dynamic system for game dramatics, pacing and difficulty.

Has been around for decades in simple forms

Was adapted for more genres over the last years


Process: MDA Framework

Mechanics Dynamics Aesthetics

The experience (Aesthetics) that arises, when the player interacts (Dynamics) with the game rules (Mechanics).

Therefore:

What Dynamics do we want to see?

What Mechanics do we employ to facilitate them?


DYNAMICS

What we want:

Smooth challenge flow

Mix of initiative and reaction

Some degree of forgiveness

Achieved with:

Spawn Rate

Attack Behavior

Recovery Rate


STRUCTURE

Intention

Definition of the goal

Dynamic

What happens

Mechanic

How to get there

Parameters

Our “balancing knobs”


Spawn Rate - Intentions

Good players are unable to ever beat the spawn counter (spawn camping)

May even need to put heavy pressure onto enemy numbers to survive incoming damage on higher modes at all

Bad players can never be swamped more than as intended by a tightly designed worst case


Spawn Rate - Dynamic

Spawn rate depends on number of enemies present, desired maximum number and time to max number

The less enemies present, the faster they spawn

Enem

y A

mount

Time

Enemy amount over time

Most fights will

happen here


Spawn Rate - Mechanic

The n-th enemy spawns after F(n) seconds after encounter start

F(n)=((n/MaxAmount)^Exp)*MaxTime

The n-th enemy spawns once a certain amount time has elapsed since spawning the previous one:

SpawnTimer=F(n)-F(n-1)

Restart the counter every time an enemy spawns

Tim

e

Enemy #

Time elapsed when nth enemy spawns

t unti

l nex

t en

emy


Spawn Rate - Parameters

MaxAmount, MaxTime and Exponent

Depend on enemy strength and encounter intensity

Manage multiple pools for different challenge categories

Larger desired max number of small enemies

Lower desired max number of strong ones

Lower time to max for “deal with it” like spawn behaviour

Larger time to max for “you cannot ignore this for long” behaviour


Attack Behavior - Intentions

Groups of two should not be boring

Groups of six+ should be tough but beatable

The player should have the initiative most of the time (ratio ~ 2:1 to 3:1) The player should be frequently forced to react

Very high intensity situations like bosses may change the initiative/reaction ratio (~1:1 or even 1:2)

The amount of players present shouldn’t influence the challenge much for an individual player


Attack Behavior - Dynamic

The enemy attack frequency depends somewhat, but not much, on actual enemy numbers

The player has enough time to dispose of 2-3 foes before reacting to something

The time between attacks depends a lot on enemy type and the attack’s strength

On lower difficulties, there is less need to react in time than on higher ones

If multiple players are present, each player is pressured more or less evenly (enemy proximity and attacks)


Attack Behavior - Mechanic

All challenging enemy actions have a cost associated

Enemies who are in position to act register all their currently possible with the Director very frequently (simultaneously)

The CD selects an action to be executed from what was registered, and incurs its cost in “debt”

The debt degenerates back to zero over time

Actions can only be ordered at zero debt Makes sure attack cost has no unwanted impact on how often has a chance to be

bought

Manage likeliness by other means (e.g. chances, or multiple debt counters)


Attack Behavior - Parameters

Per actor:

Action Cost

Combat Director

One to several debt pools

Initial debt for each pool

Degeneration rate for each pool (does not have to be constant)

Degen

erati

on

Enemy #

Enemy amount over time


Recovery Rate - Intentions

The player shouldn’t be able to hoard beneficial items (as this would trivialize bigger challenges that come along later)

The player shouldn’t ever be so starved for items that he cannot afford to use one every battle or two

There should be no extreme spikes in the drop rate


Recovery Rate - Dynamic

The drop rate of beneficial items should depend on the amount of items already in the player’s possession

The more items the player has, the less likely it is another one will drop

It should not happen that items keep dropping even though there are already plenty waiting to be picked up


Recovery Rate - Mechanic

Items waiting to be picked up count as well

Chance(Possesion)=base^(Posession)

0 < base < 1

Possession=Carried+x*OnGround

X = factor for value of items on the ground e.g. 0.5 = 50% worth

Dro

p C

hance

# in Possession

Time elapsed per enemy


Recovery Rate - Parameters

Base

OnGround Modifier (x)

Example:

Possesion = Carried+x*OnGround = 0+0.5*0 = 0

Chance(Possesion)=0.5^(0) = 1 = 100% drop chance

Possesion = Carried+x*OnGround = 1+0.5*1= 1.5

Chance(Possesion)=0.5^(1.5) = 0.353 ~ 35% drop chance

Chance(Possesion)=0.7^(1.5) = 0.585 ~ 59% drop chance


Variants

Want player to wait for opening

Have enemies buy whole sequence

Or regular low/freeze combat point generation

Want moments of frenzy

Occassionally lower costs by large factor

Want hard limits on some attacks/spawns

Add cooldown

Other Genres: e.g. Hint-Director in a Puzzle Game


THX

follow me on twitter! @swagentrotz

like us on facebook! facebook.com/BlazingBadger

enjoy gamedev ;)

keep your game in the fun zone - designing an ai director

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