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1 Game Engine Architecture Spring Introduction and overview Juha Vihavainen University of Helsinki [Gregory, Chapter 1. Introduction, pp ] [McShaffry, Chapter 2. What's in a Game ] On classroom etiquette Please, silence your cell phone while in class. Please, do not take or make phone calls in class. Please, do not keep up discussions among each other during lectures really, the lectures are voluntary and ongoing discussions disturb others wishing to listen but, of course, do ask me questions.. 2 Preliminary course outline Game subsystems and its general architecture Large-scale C++ techniques in a games context C++11/14 features (for "modern" C++ programming) essential C++ programming techniques logical modularity (concepts) vs. physical modularity (files) on programming standards and C++ style rules Simplified and component cases Miscellanous game technology, tools, and techniques Game subsystems: rendering, physics, audio, scripting..... Course prerequisites General maturity in programming object-oriented oriented concepts, data structures, etc. use of programming environments, and programming experience.. Some knowledge of C++ is required Software Design C++ (2014), or similar skills.. user-defined types, and basic OO idioms and patterns how to use pointers and manage memory in C/C++ some material on C++ will be given in the lecture notes Some knowledge on graphics programming is beneficial as background and motivation, and for optional future projects 3 4

2 Topics of GEA book include The course textbook large-scale C++ software architecture in a games context mathematics for game programming game development tools for debugging, source control and profiling subsystems including foundation systems, rendering, sound, collision, physics, character animation and game world object models multiplatform game s game programming in multiprocessor environments tools pipelines for game asset management Jason Gregory: Game Engine Architecture (2. ed., 2014) Ch. 1 Introduction what is a game/game /cases.. Ch. 2 Tools of the trade prog. envs, Visual Studio., version control, profiling, leak detection, etc. Ch. 3 Fundamentals of SE for games C++ techniques and practices Ch. 4 3D math for games points, vectors, matrices, quaternions.. Ch. 5 Engine support systems memory, strings, start-up, configs.. Ch. 6 Resources and the file system Ch. 7 Game loop and simulation main loop, and dealing with time.. Ch. 8 Human interface devices (HID) Ch. 9 Tools for debugging and developm. logging, tracing, debugging, cheats.. Ch. 10 Rendering the rendering pipeline, visual effects Ch. 11 Animation systems skeletons, poses, skinning.. Ch. 12 Collision and rigid body dynamics physics, collision detection, etc. Ch. 13 Audio (new in 2nd. edition) Ch. 14 Introduction to gameplay systems implementing game objects/worlds Ch. 15 Run-time gameplay foundations object model architectures events and message passing scripting, loading worlds.. Ch. 16 There's more? Related teaching in our department Introduction to Game Programming (Autumn 2016, 2017, 2nd period) Game Engine Architecture (this course, now: 2017, 3rd period) serves as "Game programming II" requires/teaches programming skills in C/C++ Tietokonegrafiikka (Spring 2017, 4th period, Otto Nurmi) computer graphics: rasterisation, shading, texturing.. based on OpenGL graphics library Game Project course (Spring 2017, 4th period) an optional project for IGP and GEA courses Compiler design & Code generation courses (Spring 2018) for understanding script languages and their implementation; include practical implementation projects (interpreter, compiler) Juha Vihavainen / University of Helsinki Juha Vihavainen / University of Helsinki 8

3 Using C++ in game programming XNA Game Studio / MonoGame : a "graphic " C++ is widely used in the game industry: "industrial-strength strength 3D game s are written primarily in C or C++, and any serious game programmer needs to know C++" " [Gregory, p. XXII] Games are complex applications to build multiple interactions within the program need to use visual, audio, and other resources and file formats interfacing with OS/hardware components/3rd-party party libs A sample game framework and scripting system (C#) 2D/3D games with a game predefined game skeleton, components, and 2D sprites the provides support for 2D images, IO, and audio Graphics libraries require programming knowledge of C/C++ At least, rendering and scripting s (VM) are written in C++ Most C++ programming features and techniques are relevant for game development(?) 3D scene is rendered on 2D screen: needs to use the graphics pipeline set camera and view frustum using 3D models, and shaders (GPU programs) 9 10 XNA Game Studio: a "graphic " Free tool/libraries for creating 2D and 3D games Used C# as the scripting language (an interesting choice..) Integrated with Visual Studio C# use Visual Studio 2010 for XNA version 4 (September 2010) - either Express or Full version Hardware requirements are identical to Microsoft Visual Studio Games could be run on Windows free or on Xbox 360 but did require arrangements/costs But not as powerful as many other game s (physics, GO model) was it really easy - required C# knowhow.. Engines were build on the XNA design, e.g., MonoGame Unity killed XNA?? 11 public class Game1 : Microsoft.Xna.Framework.Game { GraphicsDeviceManager graphics; public Matrix CameraView { get; set; } public Matrix CameraProjection { get; set; } public Vector3 CameraPosition ;... public Game1 () { graphics = new GraphicsDeviceManager (this); Content.RootDirectory = "Content"; } protected override void Initialize () { CameraPosition = new Vector3 (0.0f, 0.0f, f);.. CameraProjection = Matrix.CreatePerspectiveFieldOfView ( MathHelper.ToRadians (45.0f), AspectRatio, 1.0f, float.maxvalue); new Ship { Position = new Vector3 (2000, 500, 50), Rotation = MathHelper.ToRadians (40f), Scale =.75f };... base.initialize (); } protected override void Update(GameTime gametime) { if (Keyboard.GetState ().IsKeyDown (Keys.Up)) } XNA code sample CameraPosition.Y += (float)gametime.elapsedgametime.totalmilliseconds * 5;... base.update (gametime); }... rotating 3D objects & moving camera 12

4 What is a game? A "game game" " is an interactive experience that provides the player with an increasingly challenging sequence of patterns which he or she learns and eventually masters (Gregory quoting Koster, A Theory of Fun for Game Design, 2004 [26]) Gregory: "a game is a soft real-time interactive agent-based computer simulation" agent = any game entity, very often implemented as an object in an object-oriented oriented programming language The GEA textbook [Gregory] focuses on the implementation of a subset of games that comprise two- and three-dimensional virtual worlds with a small number of players (say, between 1-16): 16): primary focus will be on game s capable of producing first- person shooters, third-person action/platform games, racing games, fighting games, and the like 13 What is a game? The game term arose about the mid-1990s Doom by id Software was a FPS architected with a well-defined separation between its (1) core software components (the rendering system, the collision detection, the audio, etc.) and (2) the art assets, game worlds, and rules of play Developers began licensing games and remaking them into new products by creating new art, world layouts, weapons, characters, vehicles, and game rules with only minimal changes to the "" software Thus,, game s provide a selected set of core components, including the rendering, the collision and physics, the animation system, the audio system, the game world object model, the artificial intelligence system, etc. 14 What is a game?? (cont.) A "game " should be designed to be extensible and to be used as the foundation for many different games without major modification a game containing hard-coded logic, or any special-case case code becomes difficult or impossible to reuse to make a different game Especially, a data-driven driven architecture can separate a game from a piece of software that is a game but not an ; one definition for "data-driven": driven": all game contents & logic are driven by external data sources Note that there is also a separation between logical and physical software architecture: the inheritance/component hierarchy vs.. the source and binary file structure (very relevant for C/C++ programs) Within each game component, a number of semi-standard standard design alternatives are emerging (we can hope..) 15 What is a game?? (cont.) Originally, game s were designed to run a particular-style game (of a given "genre") on a particular hardware platform Now game s are trying to support multiple platforms,, e.g., Unreal: Windows, Xbox 360, PlayStation 3, Mac OS X, Wii U, ios, Android.. The more general-purpose a game component is, the less optimal it may be for a particular game on a particular platform as usual, optimal efficiency may require customization and trade- offs (bindings)) based on assumptions about target hardware... 16

5 The main components of a game Scene graphs (i.e., a hierarchical spatial representation of a graphical scene/level) may well need multiple different versions depending on level characteristics (outdoors, dungeon, or whatever) A rendering for 2D and/or 3D graphics A physics for more-or-less realistic world simulation and collision detection (strongly interrelated and used together) Sound and music Character animation Artificial intelligence Scripting These may also be realized as kind of subs Game (pros and cons) Benefits (mostly the same as general ones for software reuse) provides simplified access to underlying technologies organizes and speeds up development process reusing the same game (software) to create multiple different games less testing and debugging many features directly available better focus on the game design aspects enables the game to run on multiple platforms (consoles, operating systems) Drawbacks (potential costs and complexity) dependencies on the quality of design, available features, implementation decisions, licensing schemes, third-party libraries Other general game tasks Your game Initialization: : linking/using multiple different APIs and libraries Managing the game loop and real/simulation time (system clock) Reading input (and giving it meaning for game control/mechanics) Managing memory, and string/name management File systems, and resource caching (make resources available - but hide, e.g., level loading; prefetch for speed optimization) Dynamically loaded libraries (DLLs), e.g., to delay loading or to replace renderer or some other subsystem or sub Threads and thread synchronization parallel execution: multi-core, GPU, physics card (?) Network communication Shutdown 19 Graphics Sound Game API Physics AI... Hardware abstraction layer DirectX, OpenGL, Hardware layer - sound card, graphics card (physics card?) Scripting For a bit more detailed architecture, see the following slides [Gregory, p. 33]. 20

6 There are hundreds of game s, e.g.: Unreal Engine 4 (free for making free games, otherwise royalties) Unity 5 (free/professional versions) CryENGINE also free for non-commercial use.. OGRE graphics (open source) Blender game (completely free) Check out online sources ( ) Why so many graphic APIs & game s? possibly for differing target applications and requirements real-time vs. non-real real-time applications provide application specific optimizations provide genre-specific game entities and functionality provide custom platform optimizations and dependencies open source vs. manufacturer-specific APIs Game architecture by [Gregory, p. 33] (sorry, it is big) 21 A simplified GE architecture (Antti Hietasaari, 2016) Gameplay foundation systems (Game-specific subsystems) (Game- subsystems) (Utility subsystems) (Game- core systems) (Resource files) (mem. mgt, testing, math, strings, platform independence, 3rd-patry llibraries) (Parent/child model) Provide the (most direct) support for implementing the game logic "Gameplay Gameplay" " = the rules of a game world, the abilities/properties of the player and other entities in the world, and goals and objectives Related "software object model" " = the specific way to implement this : what language? use inheritance/components/templates? how to refer/identify entities (GUID), create, update, and destroy objects

7 Scripting s in game programs Potential advantages (depending on the scripting language): a convenient high-level language to control a game strongly promotes "data-driven driven design": a game should not contain any game-specific code can change the game rules/behaviour while the game is running can provide state machines, configuration, and option set up.. A script can provide parameters and actions for a game data parameters: time-of-day => determine overall lighting etc., object mass/friction, game options, AI goals and objectives behavior: set lights, move objects, select path, calculate decisions (e.g., state machines in script) Problems: : how to bind scripts to game logic and objects? performance? custom languages may lack mature development support tools (IDEs); we may have learning curve for (yet another) new language Game-specific subsystems On top of the gameplay foundation and the other low-level level components, we implement the actual game itself Typical game entities include static background geometry (buildings, roads, terrain), rigid bodies (rocks, cans, chairs), player & non-player characters, weapons, power-ups, projectiles, vehicles, lights (dynamic/ static), game-tailored cameras Tools and the asset pipeline 3D modeling tools use very complex internal data formats are rarely suitable for direct use in game software they support, e.g., full hierarchy of 3D transformations (position, orientation, scale, shear), interconnections as a directed acyclic graph (DAG) of scene nodes, edit history (for undo/redo) are often too slow to read at game run time in some cases use a closed proprietary custom format A game typically only needs a tiny fraction of all such information in order to render the model in-game; a 2-way process: 1. Data produced by a tool is first exported to a more accessible standardized format, or another custom file format 2. Exported data is further processed before being sent to the game - possibly differently for each target platform direct data flow dependencies, use [Gregory, Fig.1.35, p.55] Each needs such an asset conditioning pipeline of its own 27 Tools and the asset pipeline. 28

8 Approaches to tool architecture (in different s) Applying "model-view" architecture for games Model-view architecture (a MVC variant, here V includes C) separate content (data = "model") from view & input processing use the proven "standard" solution for GUI systems Standalone tools architecture 2. Tools share a framework with games 3. Unreal Engine's tool architecture [Gregory, Fig , p.60-61] 29 Goals and principles for game programming provide multiple views on the same shared data (game state) loose coupling between parts: update events are used for notification of changes human players, AI agents, network views can be uniformly treated an event system can provide centralized debugging/logging etc. Implementation may not be so simple need to provide a general message system (using callbacks, or applying the Observer design pattern) 30 "Ideal model-view" game architecture (sketch) Game logic state & data physics, events command interpreter game world simulation Devices: input, files RAM, time Game view... game state & commands Game view (Human) display, audio input handling Application support layer OS: PLs, DLL threads networking easy to add/replace views; provide symmetric handling of game views Game view (AI agent) stimulus interpreter decision system Game lifetime: core libs, main loop, init&shutdown Modified from [McShaffry, 2013] Example data flow in model-view system The support layer gets low-level level input from physical devices and creates input events/commands the interpreter of the human view transforms input to general game events/commands The interpreter of the game logic receives messages and updates the state of the game accordingly can handle uniformly messages from all the views: input system, AI agents, the scripting, a playback file, or network connections can also allow user commands from a screen command console (txt commands using a script, or a custom AST interpreter) sends notifications to separate views to be processed locally (or possibly to be forwarded) 31 32

9 Summary Computer games are a very specialized application area can be small (casual games), or very complicated commercial- quality interactive 3D real-time simulation systems Game s provide the foundation on which to build new game programs (very similarly to applications frameworks) provide concepts/models for a game world and its entities reuse libraries and components (also managing and hiding new versions of libraries and updating for such versions) reuse design ideas and experience Some problems are by nature general and can (possibly) be solved by standard software practices (style rules, testing, patterns,..) Hopefully, also some game-specific techniques and ideas can be identified and used as working solutions 33