Game Design Patterns
CS 4730 – Computer Game Design
Credit: Some slide material courtesy Walker White (Cornell)
CS 4730
Architecture Big Picture
Credit: Walker White
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OO to MVC
• We’ve discussed how OO doesn’t quite work
for games
– Not that we have to throw it all out of the window,
but class bloat can be a problem
• We have also discussed MVC in which
– We have a lightweight model representing world
objects
– We have a heavyweight controller in the game loop
– We have a drawing method
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The Decorator Pattern
• Remember when we discussed the decorator
pattern?
• The idea was that we could have objects that
we “hung” various functionality bits on that
would handle how that object behaved in the
world
• What if we could take that to the extreme?
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Entity-Component-System
• Another game architecture pattern is EntityComponent-System
• First really described by Scott Bilas of Gas
Powered Games and then by Adam Martin
• ECS is a pattern in which each object in the
world is completely unique (as in, is
represented by a single “primary key” integer)
• In fact, ECS works kinda like a database…
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What is an Entity?
• This might be a bit hard to swallow for OO
programmers
• What is an Entity?
– An Entity is a globally unique number
– For every discernible thing in your game-world, you
have one Entity (not one class, one actual Entity)
– Entities have no data and no methods
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What is a Component?
• A Component provides an aspect of state to an
Entity
– Want an Entity to have position in the world? Give
it a Spatial Component
– Should the Entity have health? Add a Health
Component
– Does it have velocity like a bullet? Fantastic – add
the Velocity Component
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What is a Component?
• Martin: “ALL the data goes into the
Components. ALL of it. Think you can take
some “really common” data, e.g. the x/y/z coords of the in-game object, and put it into the
Entity itself? Nope. Don’t go there. As soon as
you start migrating data into the Entity, you’ve
lost. BY DEFINITION the only valid place for the
data is inside the Component”
• Why is this?
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Abstraction
• Everything is abstracted away!
• An Entity is just a “place to hang” stuff
• It’s the combination of Components that
creates a unique in-game object!
• The Entity is simply a “primary key” that holds
all the Components together
• Then how do things get updated?
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What is a System?
• A System is a cohesive set of functionality that
does all of one thing in the game (i.e. it holds
all the behaviors)
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Collision Detection
Player Input
Enemy AI and Movement
Rendering
Enemy Spawning
Physics
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Systems
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What good does this do?
• It makes the game MUCH more modular
• You can plug-and-play pretty much anything
• You can change out functionality without
affecting the rest of the game
• And most importantly, it can make your design
data-driven
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Data-Driven Design
• Who is involved in making a video game?
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Data-Driven Design
• Who is involved in making a game?
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Programmers
Level designers
Dialogue writers
Visual artists
Musicians
Sound effects designers
Etc…
• Not all of these folks are programmers…
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Data-Driven Design
• The idea is that all content is NOT hardcoded
into the game system
• This includes:
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Art
Music
Levels
Dialogue
AI scripting
Etc…
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Data-Driven Design
• Why?
– Optimize the game creation pipeline; multiple folks
working on different things
– Makes your job of creating content MUCH easier in
general (put all the levels in one folder – when the
game starts, it loads all the levels in that folder!)
– Could support the community to create their own
content
– Easier to reuse code later (not tied to the specifics
of that game)
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Formats
• How should you create your data files?
• Art assets should be standard formats
• Scripts, dialogue, and other text info?
– XML is a reasonable option and C# has libraries to
parse it
– JSON could be an option as well, but might require
more parsing
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ECS meets Data-Driven
• Users can have more control over the game if
you let them
• Steam Workshop, for example
• And your process should be a lot easier as well
• Consider…
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World of Warcraft – Stock UI
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World of Warcraft – Modded UI
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A Game Within A Game
• I can’t tell you how much time I’ve spent
finding WoW mods…
• Example lua code for WoW:
function HelloWorld()
print("Hello, World!");
end
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A Game Within A Game
• XML Document that goes with it:
<Ui xmlns="http://www.blizzard.com/wow/ui/"
xmlns:xsi="http://www.w3.org/2001/XMLSchemainstance"
xsi:schemaLocation="http://www.blizzard.com/wow/ui/
..\..\FrameXML\UI.xsd">
<Script File="HelloWorld.lua"/>
<Frame name="HelloWorldFrame">
<Scripts>
<OnLoad>
HelloWorld();
</OnLoad>
</Scripts>
</Frame>
</Ui>
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StarWarrior Example
• See the StarWarrior MonoGame example using
the Artemis ECS Framework!
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