Animation and Games Development
242-515, Semester 1, 2014-2015
5. Game
Architecture
• Objective
o to discuss some of the main
game architecture elements,
rendering, and the game loop
242-515 AGD: 5. Game Arch.
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Overview
1.
2.
3.
4.
Simple Game Architecture
More Detailed Game Architecture
Graphics/Rendering
Game Programming
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1. Simple Game Architecture
Audio
Input
Rendering Engine
Game Logic
AI
Network
Game World
Data
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• I will focus on the graphics and maths techniques
used inside the "Rendering Engine" box.
• These include:
o basic 3D graphics theory
o 3D graphics programming with the JMonkeyEngine game
engine
o 3D rendering algorithms underlying 3D game engines
o shader programming (maybe)
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2. More Detailed Game Architecture
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2.1. Core Systems
• Elements used in most games:
startup and shutdown
file IO (loaders, writers, datafile parsers)
input controls (keyboard, mouse, touch)
window management
• minimize, maximize, full-screen, resolution
o maths (e.g. vectors, matrices)
o data structures (e.g. linked lists)
o
o
o
o
• In JMonkeyEngine, many of these come from the
standard Java libraries
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2.2. Resources (Assets)
• These can be separated into game media (stuff
visible to the player) and data resources (data used
internally by the game).
• Media Resources:
o
o
o
o
o
images / textures
audio
video
shaders
3D models
242-515 AGD: 5. Game Arch.
• Data Resources:
o user settings
• player items
• high score table
o game settings
• fonts
• physics map
o platform settings
• graphics and audio
capabilities
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2.3. Third-Party Libraries
• 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 AI
o 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)
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2.4. What is a Scene Graph?
• A scene graph stores all the entities or objects in the
scene, and the spatial relationship between them.
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• 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)
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2.5. Visual Effects (in JME)
• Particles
o smoke, fire, explosions, etc.
• Post processing / filter effects
o reflective water, light scattering, fog
o shadow mapping
o High Dynamic Range (HDR) rendering
• increased contrast for greater detail
o ambient occlusion (blocking)
o depth of field blur
o etc.
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2.6. Physics (in JME)
• Java binding to the Bullet physics library
o a collision detection and rigid body dynamics library
• http://bulletphysics.org/wordpress/
• Features include:
o
o
o
o
o
o
o
collisions, gravity, forces
mesh-accurate collision shapes
rigid body dynamics for vehicles and characters
physical joints and hinges
Blender integration
Ragdoll physics
Multi-threaded physics
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3. Graphics/Rendering
• Almost every game engine utilizes either OpenGL or
DirectX for its graphics processing and rendering.
• JMonkeyEngine uses OpenGL.
http://www.opengl.org/
http://msdn.microsoft.com/en-US/directx
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.
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3.2. DirectX
• DirectX is a Microsoft API providing direct access to
hardware.
• Only for Windows, currently at version 11.1
• DirectX components:
o
o
o
o
o
Direct Graphics – 2D and 3D graphics
DirectInput – interface to input devices
DirectAudio – play sound and music
DirectPlay – communication across networks
DirectShow – multimedia support
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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.
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3.4. What is Rendering?
render
• 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 primitives
oe.g. triangles, quadrilaterals
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4. Game Programming
• Most games consist of an startup phase,
a game loop, and a shutdown phase:
• A game loop consists of three stages:
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4.1. A Detailed
Game Flowchart
Start
Display Startup GUI
Initialization:
Load assets
Load levels
…
Read player input
Shutdown:
store scores
close files
End
game over?
Update game state,
using:
Collision Detection,
Game AI, Physics, etc
Render (draw)
game frame
4.2. Frame Rates
• 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.
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4.3. Frame Rate Problem
• 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.
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• One way to fix this speed problem is to add a "wait"
stage in the loop:
run
stop
Startup
Input
Update
Shutdown
game loop
Wait
Render
delays the loop
so the frame rate
is not too fast
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• 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:
run
stop
Startup
Input
Update
no
Shutdown
Do we have
extra time?
yes
Wait
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Render
game loop
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• 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.
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