cs 4730 game design patterns cs 4730 – computer game design credit: some slide material courtesy...
TRANSCRIPT
CS 4730
Game Design Patterns
CS 4730 – Computer Game Design
Credit: Some slide material courtesy Walker White (Cornell)
CS 47303
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
CS 47304
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?
CS 47305
Entity-Component-System• Another game architecture pattern is Entity-
Component-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…
CS 47306
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
CS 47307
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
CS 47308
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 co-ords 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?
CS 47309
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?
CS 473010
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)– Collision Detection– Player Input– Enemy AI and Movement– Rendering– Enemy Spawning– Physics
CS 473012
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
CS 473014
Data-Driven Design• Who is involved in making a game?
– Programmers– Level designers– Dialogue writers– Visual artists– Musicians– Sound effects designers– Etc…
• Not all of these folks are programmers…
CS 473015
Data-Driven Design• The idea is that all content is NOT hardcoded
into the game system• This includes:
– Art– Music– Levels– Dialogue– AI scripting– Etc…
CS 473016
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)
CS 473017
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
CS 473018
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…
CS 473021
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
CS 473022
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/XMLSchema-instance" 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>