What are game engines?

1. What are game engines? • Mark Nelson • mjas@itu.dk Fall 2013 www.itu.dk

2. What’s a game engine? Try #1 Real-time graphics engine? Maybe w/ physics? Possible features Realistic water Shadows Reflections Destructible terrain

3. What’s a game engine? Try #2 Integrated game builder? Possible features IDE Level editor 3d modeling Asset pipeline Debugging Scripting

4. Engines are lots of things Libraries Frameworks Collaboration/integration architectures Generic game shells Tools

5. No engine In the olden days, youmightcode a game by: Writing code thatimplements the game

6. Engine as library It’s sometimes nice to reuse code Collision detection Physics Sprite blitting AI

7. Engine as library

8. Engine as library Bottom-up game-enginedevelopment Write a game, thenanotherone An engine is whateveryoucanreuse Can youpackagethat up into a library (or middleware)?

9. Engine as library Engine as way of outsourcing complex but modularstuff What do youneedthat is hard to implement, but couldbeplugged in ifyou had it? AI, fancy graphics, advanced simulations, advancedphysics

10. 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

11. Engine as library v. framework Defining feature of frameworks is inversion of control And, they’re opinionated about it Your game Framework Library Your game

12. 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

13. 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]

14. 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

15. 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

16. 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.)

17. Engine as generic game Codification of genre conventions ”A Zelda-style engine” ”A platformer engine” Everything but the game A very opinionated framework

18. “Final Fantasy engine”

19. “Quake 3 engine”

20. Platformer engine

21. “Civ 5 engine” ?

22. 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

23. 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

24. 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.)