gamedesigninitiativeat cornell university

the

Mechanics Revisited

Lecture 2

gamedesigninitiativeat cornell university

the

Purpose of Today’s Lecture

� Give a review of formal design elements � Not everyone here has had the Intro Games course � And for the rest of you, it has been over a year

� Develop a deeper understanding of mechanics � Understand the important of interactions � Understand the analysis challenges

� Set us up for the later lectures on mechanics � Why do we need game grammars?

Mechanics Revisited 2

gamedesigninitiativeat cornell university

the

Actions

�  Verbs that describe what the player can do �  Walk �  Run �  Jump �  Shoot

�  Does not need to be attached to an avatar �  Build �  Swap �  Rotate

Mechanics Revisited 3

Action Platformer

(left or right) (walk, but faster!) (up; jump/run for left or right) (left or right)

(RTS or simulation) (Bejeweled clones) (Stacking games)

gamedesigninitiativeat cornell university

the

�  How do verbs, goals relate? �  Imagine there no challenges �  What verbs must you have?

�  Example: Platformers �  Goal: reach exit location �  Only need movement verbs �  Killing enemies is optional �  Other actions are secondary

�  Design Goal: Primary only �  Secondary verbs lead to bloat �  Add features with interactions

Primary Actions

Mechanics Revisited 4

gamedesigninitiativeat cornell university

the

�  Often in puzzle platformers �  Platformer verbs + something

�  “Innovation on the cheap”

�  Verb that alters “geography” �  Access hard-to-reach areas �  Directly overcome challenges �  Not directly needed for goal

�  But do this sparingly! �  Indies have one new verb! �  Other features are interactions

Secondary Actions are Acceptable

Mechanics Revisited 5

gamedesigninitiativeat cornell university

the

�  Not a direct action of player �  Outcome of the game state �  Can happen without controller

�  Example: collisions �  Accidental or player forced �  May be bad (take damage) �  May be good (gain power-up)

�  Other Examples: �  Spatial proximity �  Line-of-sight �  Resource acquisition

Interactions

Mechanics Revisited 6

gamedesigninitiativeat cornell university

the

Game Mechanics

� Game mechanic � Relationship between verbs and interactions � Often call this relationship the “rules” � Gameplay is manifestation of these rules

� Example: Joust � Verbs: Flap; go left or right �  Interaction: Collision with opponent � Rule: If hit opponent, lower player dies

Mechanics Revisited 7

gamedesigninitiativeat cornell university

the

Gameplay Example: Joust

Mechanics Revisited 8

gamedesigninitiativeat cornell university

the

�  Can we limit to one verb? �  Mechanics are all interactions

�  Common in mobile, tablet

�  Due to lack of input modes

�  Example: Sneak Beat Bandit �  Has only one verb: move

�  Rhythm game; move to beat

�  All movement on rails

�  If obstacle in way, turn

�  Line-of-sight mechanics

Design Goal: Verb Minimalism

Mechanics Revisited 9

gamedesigninitiativeat cornell university

the

Beat Sneak Bandit

Mechanics Revisited 10

gamedesigninitiativeat cornell university

the

Avoid Verb Proxies

�  Proxy: verb that activates another verb �  “Use an item” (what does the item do?)

�  “Shoot” (what does the weapon do?)

� Make your verbs outcome oriented �  Fire standard projectile (like shoot, but says what it shoots)

�  Fire freezing beam (what is does and how it is applied)

�  Important questions to ask �  Does it help me reach a goal?

�  Does it overcome a challenge?

Mechanics Revisited 11

gamedesigninitiativeat cornell university

the

Avoid Verb Proxies

�  Proxy: verb that activates another verb �  “Use an item” (what does the item do?)

�  “Shoot” (what does the weapon do?)

� Make your verbs outcome oriented �  Fire standard projectile (like shoot, but says what it shoots)

�  Fire freezing beam (what is does and how it is applied)

�  Important questions to ask �  Does it help me reach a goal?

�  Does it overcome a challenge?

Mechanics Revisited 12

Behavior is defined by interaction of projectile with the environment

gamedesigninitiativeat cornell university

the

Combining Actions

�  Verbs can combine in interesting ways �  Run and jump in a platformer �  Strafing fire in a shooter

�  Typically result of the interactions �  Each verb interacts with environment in different way �  Combination of two give extra feature for “free” �  This is an example of emergent behavior

�  Not all combinations are emergent �  Example: Double jump is not a feature of interactions �  This type of verb combination is a distinct action

Mechanics Revisited 13

gamedesigninitiativeat cornell university

the

Running Jump

�  Can move while in midair �  Just horizontal movement �  Not realistic; it is a game �  Many platformer challenges

assume this type of control

�  Different than a long jump �  Less height than reg. jump �  No control once in the air �  Would be a distinct action

Combining Actions

Strafing Fire

�  Based on “real life” property �  Bullets travel in straight line �  Movement changes origin �  Walking side-side makes a

spray (used in covering fire)

�  But some features are gamy �  Bullets slower than life �  Character faster than life �  Creates interesting effects

Mechanics Revisited 14

gamedesigninitiativeat cornell university

the

Running Jump

�  Can move while in midair �  Just horizontal movement �  Not realistic; it is a game �  Many platformer challenges

assume this type of control

�  Different than a long jump �  Less height than reg. jump �  No control once in the air �  Would be a distinct action

Combining Actions

Strafing Fire

�  Based on “real life” property �  Bullets travel in straight line �  Movement changes origin �  Walking side-side makes a

spray (used in covering fire)

�  But some features are gamy �  Bullets slower than life �  Character faster than life �  Creates interesting effects

Interaction

Interaction(?)

Mechanics Revisited 15

gamedesigninitiativeat cornell university

the

Combining Actions

Mechanics Revisited 16

Is this an example? Why or why not?

gamedesigninitiativeat cornell university

the

Interactions and Limitations

� You cannot always perform an action �  Shooting may require ammo � Cannot (always) jump in mid air

� Limitation: requirement to perform action � Boolean test (like an if-then) � Only one limitation per verb �  If more than one, split into more verbs � Example: double jump is different from jump

Mechanics Revisited 17

gamedesigninitiativeat cornell university

the

Game State

� Game State: values that represent the game world at a specific moment in time

� Interaction: function between game states

� Many of these values are spatial � Represent location of various game objects � Also physical values like velocity, acceleration

� Other changeable state values are resources � Governed by your game economy

Mechanics Revisited 18

gamedesigninitiativeat cornell university

the

Extrinsic

�  State affects other objects

�  Often detection mechanics �  Line-of-sight �  Proximity

�  But can include collisions �  Damage an opponent �  Move an object

Mechanics Revisited 19

Spatial Interactions

Intrinsic

�  State affects the player

�  Affect player resources �  Player takes damage �  Player transfers gold

�  Can effect player position �  Bounce off obstacle �  Attraction to magnet

Most difficult to handle

gamedesigninitiativeat cornell university

the

�  Current pos. → new pos. �  Which leads to new position �  Unless player can escape…

�  Game state is a vector field �  Each pos. a velocity vector �  Indicates pos. at next frame �  Implicitly defined by code

�  So you can use science of vector fields to understand �  With several caveats

Mechanics Revisited 20

Intrinsic Effects Have Feedback Loops

gamedesigninitiativeat cornell university

the

�  Convergent Singularities �  Vectors lead to line or point

�  Sucks player into a location

�  Removes player agency

�  Divergent Singularities �  Conflicting directions

�  Player “trapped” there

�  Worse than convergent

Mechanics Revisited 21

Singularities: A Design Problem

Particularly a problem in “pure physics” games.

gamedesigninitiativeat cornell university

the

�  Seeing fields helps design �  What is stable (convergent)? �  What is instable (divergent)?

�  Have to draw “possibilities” �  What if player is here? �  Rerunning physics sim at

multiple player locations �  Very compute intensive

�  Also, possibility of whom? �  Just player or other objects?

�  Visualization Ideas? Mechanics Revisited 22

Visualizing Vector Fields

gamedesigninitiativeat cornell university

the

Numeric State

�  Does not change: attributes �  Example: item strength

�  Part of data-driven design

�  Can change: resources �  Example: ammo, health

�  Often limit actions

�  Also mark “partial” success

Mechanics Revisited 23

Non-Spatial Interaction

Symbolic State

�  Lock-and-key mechanics �  Do you have item X?

�  Possession needed to pass

�  Also for “slot” mechanics �  Item gives attribute boost

�  Only one of item type

�  Creates dilemma challenge

Most difficult to handle

gamedesigninitiativeat cornell university

the

Balancing Resources

�  Sources: How a resource can increase �  Examples (player): ammunition clips, health packs �  Example (external): spawn points

�  Drains: How a resource can decrease �  Examples (player): firing weapon, player damage �  Examples (external): monster death

�  Adjust sources and sinks to “balance” economy �  Together, determine “price” of resource �  Price of resource should reflect its “power”

Mechanics Revisited 24

gamedesigninitiativeat cornell university

the

Underpricing

�  Cheap, powerful actions �  Players favor these verbs �  Limits play variety

�  Examples: �  Buff spells in most RPGs �  Dragon Age cold spells

Mechanics Revisited 25

Design Problem: Pricing Resources

Overpricing

�  Player never use resource �  Heroes IV: non-heroic units �  Raise Dead in classic RPGs

�  Waste of designers’ time

�  Player “penalized” for fun

gamedesigninitiativeat cornell university

the

Underpricing

�  Certain resources never used �  D&D 3.5: Hideous Laughter better

than Daze �  Might and Magic: Buff spells

better than damage

�  Can produce monotonous play

Mechanics Revisited 26

Design Problem: Pricing Resources

Overpricing

�  Expensive, weak actions �  Usage is “penalized” �  Waste of designers’ time

�  Examples: �  Shredder ammo in ME2 �  Raise Dead in early D&D

gamedesigninitiativeat cornell university

the

Underpricing

�  Cheap, powerful actions �  Players favor these verbs �  Limits play variety

�  Examples: �  Buff spells in most RPGs �  Dragon Age cold spells

Mechanics Revisited 27

Design Problem: Pricing Resources

Overpricing

�  Expensive, weak actions �  Usage is “penalized” �  Waste of designers’ time

�  Examples: �  Shredder ammo in ME2 �  Raise Dead in early D&D

�  Resource usage determines difficulty �  Resident Evil: Availability of ammunition �  D&D 3.x: 20% resource per encounter

gamedesigninitiativeat cornell university

the

�  Simple combat mechanic �  Each round, swap damage �  Enemy dies when health is 0

�  Player goes until health is 0 �  There is healing in game �  …but too sparse to go forever

�  Two primary characters �  Paladin: can lessen damage �  Vampire: drains blood to heal �  Which is better?

Mechanics Revisited 28

Resource Analysis: Dungelot

gamedesigninitiativeat cornell university

the

Bad Design: “Engines”

� Actions combine to make resources free � Spend one resource to get another � Use new resource to get old one back

� Example: Dragon Age � Resources: Health, Mana �  Small health loss; regain much mana �  Small mana loss; heal much damage � Solution? Cool-down time

Mechanics Revisited 29

gamedesigninitiativeat cornell university

the

�  Resource mechanics often economic transactions �  State is available resources �  Action trades old for new �  New state: result of “purchase”

�  How can we see change? �  State is high dimensional �  Paths are non-exclusive

�  Need special models �  Resource flow graphs? �  Petri Nets?

Mechanics Revisited 30

Resources Have a Visualization Problem

gamedesigninitiativeat cornell university

the

�  Level design about progress �  Sense of closeness to goal �  Choice of “paths” to goal

(dilemma challenge) �  Path choice can relate to

play style and/or difficult

�  Easier to design if discrete �  Flow-chart out progression �  Edges are mechanic(s)

�  But these state values are continuous (sort of)

Mechanics Revisited 31

Progression

gamedesigninitiativeat cornell university

the

�  Design is discretization �  Impose flow chart on state �  Each box is an equivalence

class of game states

�  Spatial Discretization �  Contiguous zones �  Example: past a doorway

�  Resource Discretization �  Range of resource values �  Example: build threshold

Mechanics Revisited 32

Discrete Progression

gamedesigninitiativeat cornell university

the

�  Is the discretization correct? �  Each game mechanic takes

one state to another state �  Is state reachable in chart? �  Is edge expected mechanic?

�  Very hard problem!

�  Idea: design building blocks �  Transitions “proven” correct �  Link together to make chart �  Motivates game grammars

Mechanics Revisited 33

Problem of Discretization

gamedesigninitiativeat cornell university

the

Summary

� Mechanics are combination actions and interactions �  Actions are a direct result of player controls �  Interactions triggered by a particular game state

�  Interactions require a understanding of game state �  Spatial state associated with physics, detection �  Resources associated with limitations, unlocking

�  Progression design is a process of discretization �  Organize state into equivalence classes �  Identify mechanics that transition between classes

Mechanics Revisited 34