Mark Nelson mjas@itu.dk

What are game engines?Fall 2013 www.itu.dk

Whats a game engine? Try #1

Real-time graphics engine?Maybe w/ physics?

Possible featuresRealistic waterShadowsReflectionsDestructible terrain

Whats a game engine? Try #2

Integrated game builder?

Possible featuresIDELevel editor3d modelingAsset pipelineDebuggingScripting

Engines are lots of things

LibrariesFrameworksCollaboration/integration architecturesGeneric game shellsTools

No engine

In the olden days, you might code a game by:Writing codethat implementsthe game

Engine as library

Its sometimes nice to reuse code

Collision detectionPhysicsSprite blittingAI

Engine as library

Engine as library

Bottom-up game-engine development

Write a game, then another oneAn engine is whatever you can reuse

Can you package that up into a library (or middleware)?

Engine as library

Engine as way of outsourcing complex but modular stuff

What do you need that is hard to implement, but could be plugged in if you had it?

AI, fancy graphics, advanced simulations, advanced physics

Engine as framework

Libraries let us reuse stuff we call out to

Can we reuse some of the structure, too?Check inputUpdate positionsCalculate dynamicsRedraw screenManage memorySync network state

Engine as library v. framework

Defining feature of frameworks is inversion of controlAnd, theyre opinionated about it

Your gameLibrary

FrameworkYour game

Engine as framework

Defines classes of stuff, and you plug in the specifics

Sprites, objects, levels, events, behaviors

Customize by extending or overriding classes

Instead of bottom-up abstraction, pattern-matching abstraction

In-class exercise

You are a 1-person programming team wanting to make a small-budget game. Do you code from scratch? Use an existing engine? If it depends, what does it depend on?

You are a 50-person team with a large budget. What about now?

[take 5 minutes to discuss]

Engine as collaboration/integration arch.

A lot of people work on a modern gameThey produce a lot of different stuff

Level designerDialog-tree writer3d modelerGraphics programmerAI programmerNetwork programmerNPC behavior scripter

Engine as collaboration/integration arch.

How do we plug all this stuff together?

An engine architecture provides modularity and interfaces

Asset pipelinesRequired functionalityDependenciesDivision of responsibilities

Engine as collaboration/integration arch.

One big boundary: code v. non-code

Architecturally: code v. data

Socially: programmers v. non-programmers

(Lots of other boundaries and interfaces.)

Engine as generic game

Codification of genre conventions

A Zelda-style engineA platformer engine

Everything but the game

A very opinionated framework

Final Fantasy engine

Quake 3 engine

Platformer engine

Civ 5 engine ?

Spectrum of engine genericity

Many engines are a mix of engine and game

Cleaner separation in more established genres

Cleaner separation from game content than dynamics

Engine as game-development tool

Unity as a game-development environmentLibrary, framework, editor, tools

Most engines have an associated toolchainSome 3rd party, e.g. MayaSome custom, e.g. level editor

Spectrum of wizardryRPG Builder, Game MakerUnityUDK

Exercise for next week

Choose an existing game and think about what engine features would make it easy to program similar gamesAn existing engine?Something new?Was the game already built on an engine (if known)?How generalizable is the game?

(Ill ask in class next week, but you wont be graded or need to hand the exercise in.)