Intro to Game Architecture

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Intro to Game Architecture

• Jeff Ward
• Associate Programmer
• Bethesda Game Studios

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My Talk

• Your first engine
• Why architect?
• Principles of OOP
• Design Patterns
• Best Practices

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Your Talk

• How can architecture help us with
• Concurrency
• Maintainability
• Code ownership
• Usability
• Performance
• Stability

4
Disclaimer

• Sorry.

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Your First Engine
AI
Creature
Renderer
Player
3DObj
Items
Bullets
2DObj
Sound
Input
File Loader
3dSnd
psst this isnt real UML
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Why is that bad?

• Bad architecture creates problems
• Produces side effects
• Hard to follow
• Hard to debug
• Hard to reuse
• Spend more time finding a way around the
  architecture than fixing the problem
• OMG HAX!

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Why Architect (Design)?

• Stability
• Reusability
• Cohesion
• Orthogonally

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A well architected system is easy to understand,
change, debug, and reuse.
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Principles of OOP

• Basics
• Encapsulation
• Inheritance
• Polymorphism
• Principles of good design
• Reduced coupling
• Increased reliability
• Increased reusability
• 10 word - orthogonality

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Encapsulation

• Encapsulation is a programming mechanism that
  binds together code and the data it manipulates,
  and that keeps both safe from outside
  interference and misuse. Schildt
• Encapsulation is not just data hiding!
• Implies each object should be a cohesive whole.

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Instance Encapsulation

• Accessing elements between instances
• Its a convenience feature, not a good idea
• Always Design for Concurrency Tip 41 in The
  Pragmatic Programmer
• Even if you dont need it, a cleaner architecture
  results.

Creature
Creature
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Inheritance

• Key overused concept of OOP
• Inherit not to reuse, but to be reused.
• Is a vs. has a vs. needs to used as a
• Degrades performance
• Prefer components over inheritance
• Cleaner architecture
• Faster execution time and overhead
• More flexibility
• More encapsulated

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Polymorphism

• Important as it relates to inheritance
• Just realize that polymorphism goes two ways
• Readable
• Unreadable

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Intro to Design Patterns

• Book Design Patterns by The Gang of Four (Gamma
  Helm Johnson Vlissides)
• The same problems keep coming up in CS
• We keep solving them in the same (or similar)
  ways.
• Is there a pattern here?

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SingletonOr Patterns Dont Solve all Problems

• Creational pattern
• Only one instance of the object exists
• Private constructor with public accessor (usually
  ClassInstance())
• Really nice name for a global
• Often overused, and often not a real solution
• Singletons translate well to factories

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Singleton Example

• Singletons (or factories) welcome
• Renderers
• Resource managers
• Memory managers
• Message queues

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Observer / Listener

• Behavioral pattern
• Inform multiple dependant objects of changes
• Usually implemented as Subject and IListener
  objects
• Listeners add themselves to subjects
• When a subject changes, all listeners are
  notified.
• Great for message queues

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Message Queues

• Built of one queue with multiple listeners

Creature
Creature
Player
Player
Queue
Vs.
Items
Bullets
Items
Bullets
NPCs
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MVCModel View Controller

• Architectural pattern
• Keeps data and representation separate
• Model data, view representation
• Controller is what sends messages to the model
  and view.
• Advantages
• One data, multiple views
• Data manipulates data, and doesnt care if its
  being viewed
• Change renderers without changing anything else

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MVC Example

• Separate view from everything else

CreatureRadarView
Creature Model
Renderer
Renderer
Creature
CreatureView
Vs.
3DObj
3DObj
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Advantages of MVC

• Complete decoupling of logic from display
• Easier to test, since you can watch just the
  logic
• Easier to change (both the display and the logic)
• Can run the view without the logic
• Can run the logic without the view
• Can distribute the logic
• So long as instances are encapsulated

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Other Quick Patterns

• Command
• An object that represents stuff that should be
  done, as an object
• Only needs to understand Execute and Undo
• Great for input handlers, macros, and undoable
  operations
• Façade
• Encapsulate an entire system by providing a
  single coherent interface
• Proxy
• A stand in for a concrete object.

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Engine Improvements
AI
Renderer
Player Model
Player View
Queue
Creature Model
Creature View
3DObj
Bullet Model
Bullet View
2DObj
Item Model
Item View
IResource
File Facade
Sound
Input
File Loader
3dSnd
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Best Practices

• Management idea
• That there is a technique that is more effective
  than any other technique at delivering positive
  results.
• Something you dont have to do, but its a good
  idea.
• Theyre like design patterns on a small scale.
• Two books
• Pragmatic Programmer by Andrew Hunt and David
  Thomas
• C Coding Standards 101 Rules, Guidelines, and
  Best Practices by Herb Sutter and Andrei
  Alexandrescu

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Examples of Best Practices

• Management Best Practices
• Use version control
• Do automated testing
• Have automated builds
• Coding Best Practices
• Prefer compile / link time errors to run time
  errors
• Give one entity one cohesive responsibility
• Prefer composition to inheritance
• Always code for concurrency (in terms of
  architecture)

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Best Practices

• Are key to your survival as a coder
• and key to your codes survival

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Final Thoughts

• Know when to refactor
• Know when to rearchitect
• Know that both are going to break everything else
• Code, Test, Refactor, Test Cycle
• Try to automate this
• Code is better at testing code than you will ever
  be.

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Summary

• Architect for cleaner, more stable, more
  reusable, and more understandable code.
• Use the principles of OOP to your advantage, not
  your detriment
• Utilize design patterns to avoid common problems
• Understand best practices and apply them.
• Make great games.

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Questions?

• jeff_at_fuzzybinary.com
• http//www.jeffongames.com