Introduction to Game Engine Design

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Introduction to Game Engine Design

• Dr. Xiaoyu Zhang

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Game Engine

• Game engine is a big program
• A game engine contains non-game-specific
  technologies and tools. Multiple games can be
  built using the same game engine
• New models, graphics, and audios etc. can be
  added the game engine to make a new game

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Main Game Loop

• Check user input
• Prepare 3D world
• Perform AI
• Collision detection
• Create or delete objects
• Modify object states?
• Object animation
• Moving objects according to physics
• Move camera
• Render and play sound

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Game Engine Subsystems

• A game engine consists of following elements
• Graphics engine
• Rendering and scene management
• Input system
• Music and sound
• Game logic and AI
• Networking
• User interface and menu system

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Graphics Engine

• Graphics engine is the central part of a game
• Rendering
• Want both speed and quality
• Based on rendering libraries as OpenGL and
  Direct3D
• Lighting and Texture mapping
• Techniques like shadow, environment mapping,
  lightmaps, particle systems (with performance
  in consideration)
• GPU programming, Cg shaders
• Algorithms to improve performance
• Back face culling
• View frustum culling (scene graph, bounding box
  )
• Visibility culling
• Level of details (LOD)

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Scene Management

• 3D World is often constructed procedurally or
  loaded from files.
• 3D scene is often organized in hierarchical scene
  graph
• Easily manageable world (traversal and rendering
  from multiple viewpoints)
• Fast culling
• Fast collision and intersection detection
• Use collision detection and game physics to add
  realism
• Collision detection and reaction
• Newtonian physics gravity, velocity, friction,
  acceleration, etc. Dont have to be physically
  accurate to have some fun

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Object Class Hierarchy

• Make a good design before writing code.
• Base class
• Render() ?
• Collision() ?
• Animate() ?
• What attributes to be included?
• What spatial data structure will you use to
  manage objects in the world?
• Do you need a generic node class for the spatial
  DS?
• Every 3D object should derive from this generic
  node class.

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Input and Audio

• Input subsystem
• Dealing with various input devices to handle user
  input and game control
• Windows event loop and DirectInput
• Game control Simple and intuitive (avoid too
  many modes)
• Sound and Music
• Enhance game playing experience greatly
• DirectX Sound API
• OpenAL (Open Audio Library www.openal.org)

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Networking

• You need networking for multi-player gaming
• Should incorporate it at design time
• There are four primary concerns in building
  networks for games
• Latency How long does it take for state to be
  transmitted
• Reliability How often is data lost or corrupted
• Bandwidth How much data can be transmitted in a
  given time
• Security How is the game-play protected from
  tampering
• DirectPlay is the DirectX communication library
• Not covered in this class

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AI and Game Rules

• Second most important component, after graphics
• Behavior of a non-player character
• Knowledge rules, knowledge bases, search
  abilities
• Environment awareness danger etc.
• Decision making rules, reasoning and learning
  abilities
• World Navigation path planning
• In FPS How does the AI get from room to room?
• In RTS User clicks on units, tells them to go
  somewhere. How do they get there? How do they
  avoid each other?
• Dynamic path planning What happens when the
  environment changes after the plan has been made?

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SimpEngine Design
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World Object Hierarchy

• Node and Object build a world hierarchy
• Node an abstract data structure representing a
  tree-like structure. It implements all structural
  operations with the hierarchy, e.g. attaching,
  detaching, traversal, and searching etc.
• Object is derived from Node. It can represent
  anything that can draw, move, collide, or even
  "think".
• Classes can further derive from Object to build
  custom objects

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Engine Core

• COGLWindow Class Creating the window and handle
  events from input devices
• CInputSystem Class An input subsystem using
  DirectInput. It has functions related to
  keyboard, mouse, and joystick
• CEngine Derived from COGLWindow.
• Implements the main message loop
• GameCycle implements game logic here
• Handle events from the input system

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Engine Core (2)

• Steps in a game cycle
• Check Input
• Prepare the world
• Perform AI
• Perform collision detection
• Calculate physics
• Move / Orient camera
• Move objects
• Play Sounds and Render the scene

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SimpEngine

• The SimpEngine class is derived from Engine.
• Has references to the camera and the world
• Has procedures to handle user input
• Camera Represents Camera object
• Controlled by mouse and keyboard
• World defines the game world
• Contains the object hierarchy
• You may want to add lighting and other features
  to the game world.
• Example

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Tips

• Get to know your group
• Know your strengths and weaknesses
• Dont be afraid to try something new
• Talk to your group and work closely
• Help out each other
• May want to try out extreme programming pair
  programming
• Integrate early and often
• Its the glue code that usually takes the most
  time
• Use CVS for version control (required)
• It may be the factor that make or break your
  project
• TortoiseCVS (www.tortoisecvs.org) - lets you work
  with files under CVS version control directly
  from Windows Explorer
• WinCVS (www.wincvs.org) does the rest, but not
  as easy to use
• Start now and have fun