Mark Nelson mjas@itu.dk

What are game engines?

Fall 2013 www.itu.dk

What’s a game engine? Try #1

Real-time graphics engine? Maybe w/ physics?

Possible features Realistic water Shadows Reflections Destructible terrain

What’s a game engine? Try #2

Integrated game builder?

Possible features IDE Level editor 3d modeling Asset pipeline Debugging Scripting

Engines are lots of things

Libraries Frameworks Collaboration/integration architectures Generic game shells Tools

No engine

In the olden days, you might code a game by: Writing code that implements the game

Engine as library

It’s sometimes nice to reuse code

Collision detection Physics Sprite blitting AI

Engine as library

Engine as library

Bottom-up game-engine development

Write a game, then another one An 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 input Update positions Calculate dynamics Redraw screen Manage memory Sync network state

Engine as library v. framework

Defining feature of frameworks is inversion of control And, they’re opinionated about it

Your game Your game

LibraryLibrary

Framework Framework

Your gameYour 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 game They produce a lot of different stuff

Level designer Dialog-tree writer 3d modeler Graphics programmer AI programmer Network programmer NPC behavior scripter

Engine as collaboration/integration arch.

How do we plug all this stuff together?

An engine architecture provides modularity and interfaces

Asset pipelines Required functionality Dependencies Division 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 engine” ”A 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 environment Library, framework, editor, tools

Most engines have an associated toolchain Some 3rd party, e.g. Maya Some custom, e.g. level editor

Spectrum of wizardry RPG Builder, Game Maker Unity UDK

Exercise for next week

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

(I’ll ask in class next week, but you won’t be graded or need to hand the exercise in.)