Intro to Architecture

8/6/2019 Intro to Architecture

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Intro to Game Architecture

Jeff Ward

Associate Programmer Bethesda Game Studios



My Talk

Your first engine

Why architect?

Principles of OOP Design Patterns

Best Practices



Y our Talk

How can architecture help us with:

Concurrency

Maintainability

Code ownership

Usability

Performance

Stability



Disclaimer

Sorry.



AI

Y our First Engine

psst« this isn¶t real UML«

Renderer

3DObj

2DObj

Player Creature

Sound

3dSnd

Input

Items Bullets

File Loader



W hy 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 H AX!



W hy Architect ( Design)?

Stability

Reusability

Cohesion Orthogonally



A well architected sy stem is easy

to understand, change, debug,

and reuse.



Principles of OOP

Basics

Encapsulation

Inheritance

Polymorphism Principles of good design

Reduced coupling

Increased reliability

Increased reusability $10 word - orthogonality



Encapsulation

³Encapsulation 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.



Instance Encapsulation

Accessing elements between instances

It¶s a convenience feature, not a good idea

³Always Design for Concurrency´ ± Tip 41 in ThePragmatic Programmer

Even if you don¶t need it, a cleaner architecture results.

Creature Creature



Inheritance

Key overused concept of OOP

³ Inherit not to reuse, but to be reused.´

³Is a´ vs. ³has a´ vs. ³needs to used as a´

Degrades performance

Prefer components over inheritance Cleaner architecture

Faster execution time and overhead

More flexibility

More encapsulated



Poly morphism

Important as it relates to inheritance«

Just realize that polymorphism goes two ways

Readable

Unreadable



Intro to Design Patterns

Book Design Patterns by ³The 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?



SingletonOr ´Patterns Don·t Solve all Problemsµ

Creational pattern

Only one instance of the object exists

Private constructor with public accessor (usuallyClass::Instance())

Really nice name for a global

Often overused, and often not a real solution

Singletons translate well to factories



Singleton Example

Singletons (or factories) welcome«

Renderers

Resource managers

Memory managers

Message queues



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



Message Queues

Built of one queue with multiple listeners

Player Creature

Items Bullets

Vs.Player Creature

Items Bullets

Queue

NPCs



MVCModel V iew Controller

Architectural pattern

Keeps data and representation separate

Model = data, view = representation

Controller is what sends messages to the model andview.

Advantages

One data, multiple views

Data manipulates data, and doesn¶t care if its being viewed Change renderers without changing anything else



MVC Example

Separate view from everything else

Renderer

3DObj

Creature

Vs.

Creature Model

CreatureView

Renderer

3DObj

CreatureRadarView



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



Other Quick Patterns

Command An object that represents stuff that should be

done, as an object

Only needs to understand ³Execute´ and ³Undo´ Great for input handlers, macros, and undoable

operations

Façade

Encapsulate an entire system by providing asingle coherent interface

Proxy A stand in for a concrete object.



Engine Improvements

AI

Renderer

3DObj

2DObj

Player Model

Sound

3dSnd

Input File Loader

Creature Model

Item Model

Bullet Model

Player View

Creature View

Item View

Bullet View

Queue

File Facade

IResource



Best Practices

Management idea

That there is a technique that is more effective than anyother technique at delivering positive results.

Something you don¶t have to do, but it¶s a good idea. They¶re like design patterns on a small scale.

Two books:

Pragmatic Programmer by Andrew Hunt and DavidThomas

C++ Coding Standards: 101 Rules, Guidelines, and BestPractices by Herb Sutter and Andrei Alexandrescu



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)



Best Practices

Are key to your survival as a coder«

« and key to your code¶s survival



Final Thoughts

Know when to refactor

Know when to rearchitect

Know that both are going to break everythingelse

Code, Test, Refactor, Test Cycle

Try to automate this

Code is better at testing code than you will ever be.



Summary

Architect for cleaner, more stable, morereusable, and more understandable code.

Use the principles of OOP to your advantage,not your detriment

Utilize design patterns to avoid commonproblems

Understand best practices and apply them. Make great games.



Questions?

[email protected]

http://www.jeffongames.com

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