242-515 AGD: 5. Game Arch.

1

• Objectiveo to discuss some of the main

game architecture elements, rendering, and the game loop

Animation and Games

Development242-515, Semester 1, 2014-2015

5. Game Architecture

242-515 AGD: 5. Game Arch.

2

1. Simple Game Architecture2. More Detailed Game Architecture3. Graphics/Rendering4. Game Programming

Overview

1. Simple Game Architecture

Rendering EngineGame Logic

AI

Audio

Game WorldData

Input

Network

3

• I will focus on the graphics and maths techniques used inside the "Rendering Engine" box.

• These include:o basic 3D graphics theoryo 3D graphics programming with the JMonkeyEngine game

engineo 3D rendering algorithms underlying 3D game engineso shader programming (maybe)

4

242-515 AGD: 5. Game Arch.

5

2. More Detailed Game Architecture

242-515 AGD: 5. Game Arch.

6

• Elements used in most games:o startup and shutdowno file IO (loaders, writers, datafile parsers)o input controls (keyboard, mouse, touch)o window management

• minimize, maximize, full-screen, resolutiono maths (e.g. vectors, matrices)o data structures (e.g. linked lists)

• In JMonkeyEngine, many of these come from the standard Java libraries

2.1. Core Systems

242-515 AGD: 5. Game Arch.

7

• These can be separated into game media (stuff visible to the player) and data resources (data used internally by the game).

2.2. Resources (Assets)

• Data Resources:o user settings

• player items• high score table

o game settings• fonts• physics map

o platform settings• graphics and audio

capabilities

• Media Resources:o images / textureso audioo videoo shaderso 3D models

242-515 AGD: 5. Game Arch.

8

• The game engine will often reuse existing libraries:o GUI (in JMonkeyEngine (JME): Nifty GUI)o Physics (in JME: jBullet, a Java port of the Bullet Physics

library)o skeletons (in JME: support for Blender joints)o AIo visual effects( in JME: OpenGL shaders, particle system)o terrain (in JME: the Ogre3D dotScene format)

o scene graph (so important, that it's a part of the core in JME)

2.3. Third-Party Libraries

242-515 AGD: 5. Game Arch.

9

• A scene graph stores all the entities or objects in the scene, and the spatial relationship between them.

2.4. What is a Scene Graph?

242-515 AGD: 5. Game Arch.

10

• The scene graph data structure simplifies the creation of a scene by the user, and also:o makes it easier to transform groups of objects

• e.g. translate, rotate them

o makes it easier to determine when objects are colliding and are visible to each other

o makes it easier to display a scene with different Levels of Detail (LOD)

242-515 AGD: 5. Game Arch.

11

• Particleso smoke, fire, explosions, etc.

• Post processing / filter effectso reflective water, light scattering, fogo shadow mappingo High Dynamic Range (HDR) rendering

• increased contrast for greater detailo ambient occlusion (blocking)o depth of field bluro etc.

2.5. Visual Effects (in JME)

242-515 AGD: 5. Game Arch.

12

• Java binding to the Bullet physics libraryo a collision detection and rigid body dynamics library

• http://bulletphysics.org/wordpress/

• Features include:o collisions, gravity, forceso mesh-accurate collision shapeso rigid body dynamics for vehicles and characters o physical joints and hingeso Blender integrationo Ragdoll physicso Multi-threaded physics

2.6. Physics (in JME)

3. Graphics/Rendering

• Almost every game engine utilizes either OpenGL or DirectX for its graphics processing and rendering.

• JMonkeyEngine uses OpenGL.

http://msdn.microsoft.com/en-US/directxhttp://www.opengl.org/

3.1. OpenGL• A hardware-independent API, implemented on

many different platforms.

• Several hundred functions, with many language bindings.

• An accepted industry standard:• evolves slowly• currently at version 4.2

• Widely used for:• games, modeling, scientific visualization, etc.

14

3.2. DirectX• DirectX is a Microsoft API providing direct access

to hardware.• Only for Windows, currently at version 11.1• DirectX components:

o Direct Graphics – 2D and 3D graphicso DirectInput – interface to input deviceso DirectAudio – play sound and musico DirectPlay – communication across networkso DirectShow – multimedia support

15

3.3. OpenGL vs. DirectX

• OpenGL is aimed at 3D graphics only; DirectX is a more complete game development API.

• OpenGL is portable across platforms; DirectX is only for Windows.

16

3.4. What is Rendering?

• Rendering is the process of converting a 3D scene into a 2D picture (raster image) on the computer screen:                                          o The 3D scene is composed of 3D models (geometries).o A model is composed of 3D graphics primitiveso e.g. triangles, quadrilaterals

17

render

242-515 AGD: 5. Game Arch.

18

4. Game Programming• Most games consist of an startup phase,

a game loop, and a shutdown phase:

• A game loop consists of three stages:

4.1. A Detailed Game Flowchart

Read player input

Update game state,using:Collision Detection,Game AI, Physics,

etc

Shutdown: store scores close files game over?

Initialization: Load assets Load levels …

Start

Display Startup GUI

Render (draw)game frameEnd

242-515 AGD: 5. Game Arch.

20

• An important element missing from the basic game loop is the need to keep the rate of frame drawing constant.

• A frame rate is the average number of frames drawn by the game loop each second.

• Typical frame rates:o 30 fps (i.e. 30 frames drawn in 1 second)o 50 fps

• The frame rate should stay constant so that the user sees the game updating at a fixed rate.

4.2. Frame Rates

242-515 AGD: 5. Game Arch.

21

• The frame rate should be the same on fast and slow computers.

• The problem is that a fast machine will carry out "updating" and "rendering" faster than a slow machine, and so the frame rate will be faster.

• We must change the game loop so that the frame rate isn't affected by a computer's speed.

4.3. Frame Rate Problem

242-515 AGD: 5. Game Arch.

22

• One way to fix this speed problem is to add a "wait" stage in the loop:

delays the loopso the frame rateis not too fast

UpdateStartup Input

RenderWait

Shutdown

stoprun

game loop

242-515 AGD: 5. Game Arch.

23

• Waiting deals with a loop that is too fast, but what about a loop that is too slow?o e.g. because the computer is slow

• One solution is to skip the rendering (drawing) stage, making the loop faster:

UpdateStartup Input

RenderWait

Shutdown

stoprun

game loop

Do we haveextra time?

yes

no

242-515 AGD: 5. Game Arch.

24

• The good news is that JMonkeyEngine deals with maintaining a constant frame rate.

• We only have to write the "update" code for the loop, not the "rendering" or timing parts, which are dealt with by the engine.