dm6111 games engine architecture

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DM6111Games engine architecture

DM6111DM6111Games engine architectureGames engine architecture

Dioselin GonzalezJan – Feb 2007

Dioselin GonzalezJan – Feb 2007


1. Intro1. Intro1. Intro

Some free/OS enginesSome free/OS engines

• XNA Game Studio Express– msdn.microsoft.com/directx

• OGRE– www.ogre3d.org

• Crystal Space– www.crystalspace3d.org/main/Main_Page


• Delta3D– www.delta3d.org

• Panda3D– www.panda3d.org

• Quake{2,3,4}– www.idsoftware.com


• HGE– hge.relishgames.com

• PopCap– developer.popcap.com

THE GAME LOOPTHE GAME LOOP

The main : why?The main : why?L o o o o o o pL o o o o o o p

EXCELEXCEL WOWWOW

Open documentOpen document

Wait for commandWait for command

Process commandProcess command

ExitExit

Linear + app waits for youLinear + app waits for you

Trademarks are property of their respective owners Trademarks are property of their respective owners

The main : why?The main : why?The main : why?L o o o o o o pL o o o o o o p

EXCELEXCEL WOWWOW




ExitExit


HumanHuman--Troll duelTroll duel

Hunter training Hunter training a peta pet

Monster attacking Monster attacking you from behindyou from behind



EXCELEXCEL WOWWOW

NonNon--linear, simulation keeps running linear, simulation keeps running even when you don’t do anythingeven when you don’t do anything

HumanHuman--Troll duelTroll duel

Hunter training Hunter training a peta pet

Monster attacking Monster attacking you from behindyou from behind





ExitExit



ONE computer, ONE cpu, processing ONE instruction at a time

(in a simplified example…)

The mainThe main L o o o o o o pL o o o o o o p

Process player inputProcess player input

Do game logicDo game logic

Present game Present game state to all viewsstate to all views

2525--30 fps 30 fps (at least)(at least)

TermsTerms

• Tick – one iteration

GameLogic

TickAllAI();

TickAllParticles();

TickAllPhysics();

TickAllMovement();

while (true) {GameAppLayer->GetUserInput(); GameLogic->TickAllAI();GameLogic->TickAllParticles();GameLogic->TickAllPhysics();GameLogic->TickAllMovement();

}

Main loopMain loop

IT3157 slides by Mr. Wee Juan TanIT3157 slides by Mr. Wee Juan Tan

Tick, tick, tick, tick…Tick, tick, tick, tick…

• Some TickXXX() can be executed quickly.– A simple A.I. processing takes << 0.01 ms to

complete

• Some take longer– Graphics may take >30ms

– Can be solved by using lower polygon count, hardware acceleration, scenegraphs, etc

IT3157 slides by Mr. Wee Juan TanIT3157 slides by Mr. Wee Juan Tan


2. GUI2. GUI2. GUI

Graphical User InterfaceGraphical User Interface

• 2D layer– scalar vector (SVG) or raster graphics [Robin Tan’s

IT3935 slides]

– Issues?

• Keyword: widget– Short for ‘window gadget’, it refers to

components in a graphical user interface [www.cs.ucc.ie/~dgb/courses/swd/glossary.html]

– Event-driven, derive from base class

Graphical User InterfaceGraphical User Interface

• GUI libraries– GLUT (freeGLUT), GLUI, DirectX UI, MFC

– SDL, wxWidgets, FLTK, Crazy Eddie GUI, OpenGUI, TrollTech’s QT, …

A “hello world” example…A “hello world” example…


3. Input3. Input3. Input

Game architectureGame architecture

Game Application LayerGame Application Layer

Game Logic Game View

McShaffryMcShaffry, M. (2005). Game coding complete. 2, M. (2005). Game coding complete. 2ndnd ed. Arizona, US: ed. Arizona, US: ParaglyphParaglyph Press.Press.

HW and OSHW and OS

Application layerApplication layer

Game application layer

DevicesDevices Operating System Game lifetime

InputInput FilesFiles RAMRAM TimeTime Language DLL Threads Network CoreLibs

MainLoop

Init &shutdown

McShaffryMcShaffry, M. (2005). Game coding complete. 2, M. (2005). Game coding complete. 2ndnd ed. Arizona, US: ed. Arizona, US: ParaglyphParaglyph Press.Press.

cross-platform libraries deal with underlying hardware device layer

An example…An example…

Viewing & Input Topics : Viewing & Input Topics : PickingPicking

To detect which objects are below the To detect which objects are below the mouse or in a square region of the window mouse or in a square region of the window

WarcraftWarcraft® III: Reign of Chaos™® III: Reign of Chaos™

©2002 Blizzard Entertainment, Inc.. All rights reserved. Reign o©2002 Blizzard Entertainment, Inc.. All rights reserved. Reign of Chaos is a trademark and f Chaos is a trademark and WarcraftWarcraft and Blizzard Entertainment are trademarks or and Blizzard Entertainment are trademarks or registered trademarks of Blizzard Entertainment, Inc. in the U.Sregistered trademarks of Blizzard Entertainment, Inc. in the U.S. and/or other countries.. and/or other countries.

PickingPicking

((win_xwin_x, , win_zwin_z))

((obj_xobj_x, , obj_yobj_y, , obj_zobj_z))

From Windows From Windows coordinates to coordinates to World coordinatesWorld coordinates

3D model from 3D model from www.itswww.its--ming.comming.com//

Picking in OpenGLPicking in OpenGL

• GL provides GL_SELECTION render mode

1. Init names and selection buffer#define BODY 1#define HEAD 2 glSelectBuffer(int buffersize, unsigned int *buffer);

2.Enter selection modeglRenderMode(GL_SELECT);



3. “Draw” the scene as usual, give “names” to objects and define “pickable” area. gluPickMatrix((double) xmouse, (double)

(viewport[3] - ymouse), pickwidth, pickheight, viewport);

glInitNames(0); glPushName(BODY); render_body; glPushName(BODY); //etc…



4. Leave selection mode and return to render modehits = glRenderMode(GL_RENDER);

5. Process the hit recordsif (hits != 0) {

//process, highlight, etc…//using selection buffer

}


• Other methods– Render each primitive in a unique color

• Use glReadPixels() to read single pixel under mouse location

– Shoot a pick ray through the mouse location • Call gluUnProject() twice

Viewing & Input Topics : Viewing & Input Topics : ZoomingZooming

FrustumFrustum

Near (front)Near (front)

Far (back)Far (back)


FrustumFrustum

glFrustum(xmin,xmax, ymin, ymax, near, far)

gluPerspective(fovy, aspect, near, far)

fovyfovy

WidthWidth

HeightHeight


Q&D zoom in OpenGLQ&D zoom in OpenGL

1. Uniform scale on ModelView matrix• glScale3f(0.25f,0.25f,0.25f)

• Often results in clipping by z-near and z-far

2. A better method is to play with the view volume…

Q&D zoom in OpenGLQ&D zoom in OpenGL

Maintain a zoom factorGLfloat zoom_factor = 1.0f; // 0 <= zf <= 1

a. Modify field of viewgluPerspective (50.0*zoomFactor,

(float)width/(float)height, zNear, zFar);

OR

b. Change frustumglFrustum(left*zoomFactor, right*zoomFactor,

bottom*zoomFactor, top*zoomFactor, zNear, zFar);


4. Physics4. Physics4. Physics

Simultaneous eventsSimultaneous events

• How to make many things continuously happen at the same time?

Simultaneous eventsSimultaneous events

• How to make many things continuously happen at the same time?

Move/Process/Modify each one bit at a time

Simultaneous movementSimultaneous movement

Frame 0Frame 0Frame 1Frame 1Frame 2Frame 2Frame 3Frame 3

Simultaneous movementSimultaneous movement

Frame 0Frame 0Frame 1Frame 1Frame 2Frame 2Frame 3Frame 3

When you play it at 30 fps….When you play it at 30 fps….

Basic movementBasic movement

Going one level down:

How to move each object?

Move all objectsMove all objects

Move car (a little)Move car (a little) Move ball (a little)Move ball (a little)

Basic movement : common modelBasic movement : common model

1. For each object, store its position P and direction D

P = (P = (x,yx,y))

xx

yy

DirectionDirection


2. Position and Direction are vectors, Direction is normalized.

P = (P = (x,yx,y))

xx

yy

D = (d1, d2)D = (d1, d2)


3. Multiply D by a DisplacementFactor (df) and obtain a Displacement vector (DV)

P = (P = (x,yx,y))

xx

yyD = (d1, d2)D = (d1, d2)

DV = DV = dfdf*D*D= = dfdf*(d1,d2)*(d1,d2)= (= (dfdf*d1,df*d2)*d1,df*d2)


4. Add P and Displacement vector to obtain new position

PP00 = (= (x,yx,y))

xx

yy D = (d1, d2)D = (d1, d2)DV = DV = dfdf*(d1,d2)*(d1,d2)

PP11 = (= (x,yx,y) + DV) + DV= (= (x,yx,y) + () + (dfdf*d1,df*d2)*d1,df*d2)= (= (x+dfx+df*d1, *d1, y+dfy+df*d2)*d2)


4. Add P and Displacement vector to obtain new position

xx

yy


Position (P)Position (P)

xx

yyDirection (D)Direction (D)

Displacement Vector Displacement Vector (DV)(DV)

Displacement Factor (Displacement Factor (dfdf) = ) = length(DVlength(DV))

• Displacement Factor (df) is a number

• A fixed df will result in same distance traveled each frame– But ????


FrameFrame--rate Independent rate Independent MovementMovement


Position (P)Position (P)

xx

yyDirection (D)Direction (D)

Displacement Vector Displacement Vector (DV)(DV)

Displacement Factor (Displacement Factor (dfdf) = ) = length(DVlength(DV))

• Displacement Factor (df) is a number

• A fixed df will result in same distance traveled each frameDifferent computers have different frame rates

Movement will be faster in some machines


Setting your car in cruise controlSetting your car in cruise control

See See http://auto.howstuffworks.com/cruisehttp://auto.howstuffworks.com/cruise--control.htmcontrol.htm

160 km/h160 km/h

160 km/h160 km/h

Pentium® DPentium® DGeForceGeForce® 7® 7

Pentium® IIPentium® IIGeForceGeForce® 2® 2

timetime(seconds)(seconds)tt00 tt11 tt22

Setting your car in cruise controlSetting your car in cruise control

See See http://auto.howstuffworks.com/cruisehttp://auto.howstuffworks.com/cruise--control.htmcontrol.htm

160 km/h160 km/h

160 km/h160 km/h

Pentium® DPentium® DGeForceGeForce® 7® 7

Pentium® IIPentium® IIGeForceGeForce® 2® 2

timetime(seconds)(seconds)tt00 tt11 tt22

Time becomes an important factorTime becomes an important factor

Keep track of…Keep track of…

1. At which speed do you want to travel?

160 Km160 Km 1 hour1 hour

? Km? Km 1/3600 hour1/3600 hour

? = 1/3600 x 160? = 1/3600 x 160

2. How much time has passed?

In your game…In your game…

Game_start {- Set desired speed- Record start time

}

Main_loop{1. See how much time has passed2. Calculate DF using time and speed

}

In your code…In your code…

Game_start {Direction = (0.0, 0.0, -1.0);Speed = 16; //this is world units per secondt0 = current_time;

}

In your code…In your code…

Game_start {Direction = (0.0, 0.0, -1.0);Speed = 16; //this is world units per secondt0 = current_time;

}Main_loop {

t1 = current_time;elapsed_time = t1 – t0;DF = Speed * elapsed_time;Position += DF * Direction;t0 = t1;

}

In your code…In your code…Game_start {

Direction = (0.0, 0.0, -1.0);Speed = 16; //this is world units per secondglutInit(&argc, argv);int t0 = glutGet(GLUT_ELAPSED_TIME); //milliseconds!

}

Main_loop {int t1 = glutGet(GLUT_ELAPSED_TIME); elapsed_time = (t1 – t0)/1000.0; //secondsDF = Speed * elapsed_time;Position += DF * Direction;t0 = t1;

}

Image credits / referencesImage credits / references

• http://devimg.net

• http://fly.srk.fer.hr/~unreal/theredbook/

• http://www.lighthouse3d.com/opengl/viewfrustum/

• http://www.opengl.org/resources/faq/technical/viewing.htm

• http://www.lighthouse3d.com/opengl/picking/

• http://www.cse.ucsc.edu/classes/cmps160/Fall01/picking.txt

• http://www.opengl.org/resources/faq/technical/selection.htm

• http://www.cs.utah.edu/~xchen/columbia/session2/lec31/html/index.html

• IT3157 slides prepared by Mr. Wee Juan Tan

http://devimg.net/

http://fly.srk.fer.hr/~unreal/theredbook/

http://www.lighthouse3d.com/opengl/viewfrustum/

http://www.opengl.org/resources/faq/technical/viewing.htm

http://www.lighthouse3d.com/opengl/picking/

http://www.cse.ucsc.edu/classes/cmps160/Fall01/picking.txt

http://www.opengl.org/resources/faq/technical/selection.htm

http://www.cs.utah.edu/~xchen/columbia/session2/lec31/html/index.html

http://www.cs.utah.edu/~xchen/columbia/session2/lec31/html/index.html

dm6111 games engine architecture

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