3D Game Programming

OpenGL3D Game Programming

OpenGLMing-Te Chi

Department of Computer Science, National Chengchi University

OutlineOutline

Coordinate system

Basic OpenGL Program

GLUT – event loop– IO

Cartesian PlaneCartesian Plane

(0, 0)

(4, 3)

(-3, -2)

+x

+y

+z

Coordinate Clipping Coordinate Clipping

(0, 0) +x

+y

(150, 100)

(-75, -50)

(75, 50)

ViewportViewport

Mapping drawing coordinates to windows coordinates

Window spaceclipping space

(0, 0) +x

+y

ProjectionProjection

Getting 3D to 2D– Orthographic projections

– Perspective projections

Representing VisualsRepresenting Visuals

3D objects– Mesh: geometry– Materials– Texture maps

Lighting

Shader

OpenGL and GLUT OverviewOpenGL and GLUT Overview

What is OpenGL ? What can it do for me?OpenGL in windowing systemsWhy GLUTA GLUT program template

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What Is OpenGL?What Is OpenGL?

Graphics rendering API– high-quality color images composed of

geometric and image primitives

– window system independent

– operating system independent

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SGI and GLSGI and GL

Silicon Graphics (SGI) revolutionized the graphics workstation by implementing the pipeline in hardware (1982)To access the system, application

programmers used a library called GLWith GL, it was relatively simple to

program three dimensional interactive applications 10

OpenGLOpenGL

The success of GL lead to OpenGL (1992), a platform-independent API that was – Easy to use– Close enough to the hardware to get

excellent performance– Focus on rendering– Omitted windowing and input to avoid

window system dependencies

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OpenGL EvolutionOpenGL Evolution

Originally controlled by an Architectural Review Board (ARB) Members included SGI, Microsoft, Nvidia,

HP, 3DLabs, IBM,……. Relatively stable (present version 4.2)

▪ Evolution reflects new hardware capabilities▪ 3D texture mapping and texture objects▪ Vertex programs

Allows for platform specific features through extensions

ARB replaced by Khronos

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Revolution of GPURevolution of GPU

Graphics Process Unit (GPU)

OpenGL generationOpenGL generation

Timeline of OpenGLTimeline of OpenGL Aug

OpenGL 4.2

OpenGL LibrariesOpenGL Libraries

OpenGL core library

OpenGL32 on Windows

GL on most unix/linux systems (libGL.a)

OpenGL Utility Library (GLU)

Provides functionality in OpenGL core but avoids having to

rewrite code

Links with window system

GLX for X window systems

WGL for Windows

AGL for Macintosh

OpenGL ArchitectureOpenGL Architecture

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DisplayList

PolynomialEvaluator

Per VertexOperations &PrimitiveAssembly

RasterizationPer FragmentOperations

FrameBuffer

TextureMemory

CPU

PixelOperations

OpenGL as a RendererOpenGL as a Renderer

Geometric primitives– points, lines and polygons

Image Primitives– images and bitmaps– separate pipeline for images and

geometry• linked through texture mapping

Rendering depends on state– colors, materials, light sources, etc.

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Related APIsRelated APIs

AGL, GLX, WGL– glue between OpenGL and windowing systems

GLU (OpenGL Utility Library)– part of OpenGL– NURBS, tessellators, quadric shapes, etc.

GLUT (OpenGL Utility Toolkit)– portable windowing API– not officially part of OpenGL

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OpenGL and Related APIsOpenGL and Related APIs

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GLUT

GLU

GL

GLX, AGLor WGL

X, Win32, Mac O/S

software and/or hardware

application program

OpenGL Motifwidget or similar

OpenGL-related ecosystemOpenGL-related ecosystem

PreliminariesPreliminariesHeaders Files

#ifdef WIN32#include <windows.h> // Must have for Windows platform builds#include "glee.h" // OpenGL Extension "autoloader"#include <gl\gl.h> // Microsoft OpenGL headers (version 1.1 by themselves)#include <gl\glu.h> // OpenGL Utilities#include <gl\glut.h> // Glut (or freeglut). Depend on the install dictionary#endif

Libraries (win32)– opengl32.lib– glu32.lib– glut32.lib

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Enumerated Types– OpenGL defines numerous types for

compatibility– GLfloat, GLint, GLenum, etc.

Notes on compilationNotes on compilation

See website and ftp for examplesUnix/linux

– Include files usually in …/include/GL– Compile with –lglut –lglu –lgl loader flags– May have to add –L flag for X libraries– Mesa implementation included with

most linux distributions– Check web for latest versions of Mesa

and glut

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Compilation on WindowsCompilation on Windows

Visual C++– Get glut.h, glut32.lib and glut32.dll from

web– Create a console application– Add opengl32.lib, glu32.lib, glut32.lib to

project settings (under link tab)

Cygwin (Linux under Windows)– Can use gcc and similar makefile to linux– Use –lopengl32 –lglu32 –lglut32 flags

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Compilation on Mac OSXCompilation on Mac OSX

OpenGL and GLUT come with the OS and Xcode installations. To verify, check for:

/Library/Frameworks/{OpenGL,GLUT}.framework

– Use -framework GLUT -framework OpenGL flags

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GLUT (OpenGL Utility Toolkit) GLUT (OpenGL Utility Toolkit)

GLUT was originally written by Mark Kilgard to support the sample programs in the second edition OpenGL 'RedBook‘Latest version– glut-3.7.6-bin.zip (117 KB) since 2001!

Strict licenseSweet alternative– freeglut – http://freeglut.sourceforge.net/docs/api.php

GLUT BasicsGLUT Basics

Application Structure– Configure and open window– Initialize OpenGL state– Register input callback functions

• render• resize• input: keyboard, mouse, etc.

– Enter event processing loop

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GLUT Sample ProgramEvent

GLUT Sample ProgramEventInt main( int argc, char** argv ){ int mode = GLUT_RGB|GLUT_DOUBLE;

glutInitDisplayMode( mode ); glutCreateWindow( argv[0] ); init();

glutDisplayFunc( display ); glutReshapeFunc( resize ); glutKeyboardFunc( key ); glutIdleFunc( idle );

glutMainLoop();

return 0;}

Idle

Event Loop

OpenGL and WindowsInitialization

Callback function Registration

Get Event

Process Event

OpenGL InitializationOpenGL Initialization

Set up whatever state you’re going to use

void init( void )

{

glClearColor( 0.0, 0.0, 0.0, 1.0 );

glClearDepth( 1.0 );

glEnable( GL_LIGHT0 );

glEnable( GL_LIGHTING );

glEnable( GL_DEPTH_TEST );

}

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GLUT Callback FunctionsGLUT Callback Functions

Routine to call when something happens– window resize or redraw– user input– animation

“Register” callbacks with GLUTglutDisplayFunc( display );glutIdleFunc( idle );glutKeyboardFunc( keyboard );

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OpenGL Command FormatsOpenGL Command Formats

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glVertexglVertex33ffvv( ( vv ) )

Number ofNumber ofcomponentscomponents

2 - (x,y) 2 - (x,y) 3 - (x,y,z)3 - (x,y,z)4 - (x,y,z,w)4 - (x,y,z,w)

Data TypeData Typeb - byteb - byteub - unsigned byteub - unsigned bytes - shorts - shortus - unsigned shortus - unsigned shorti - inti - intui - unsigned intui - unsigned intf - floatf - floatd - doubled - double

VectorVector

omit “v” foromit “v” forscalar formscalar form

glVertex2f( x, y )glVertex2f( x, y )

Rendering CallbackRendering Callback

Do all of your drawing here• glutDisplayFunc(glutDisplayFunc( display display ););

void display( void ){ glClear( GL_COLOR_BUFFER_BIT ); glBegin( GL_TRIANGLE_STRIP ); glVertex3fv( v[0] ); glVertex3fv( v[1] ); glVertex3fv( v[2] ); glVertex3fv( v[3] ); glEnd(); glutSwapBuffers();}

Idle CallbacksIdle Callbacks

Use for animation and continuous update

glutIdleFunc( glutIdleFunc( idleidle ); );

void idle( void ){ t += dt; glutPostRedisplay();}

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Animation in GLUT alternativeAnimation in GLUT alternative– glutIdleFunc

• Sets the global idle callback.

• Only one idle function

• Can be easily stopped by

– Call glutPostRedisplay to refresh the screen

void glutIdleFunc ( void (*func)());

glutIdleFunc ( NULL );

User Input CallbacksUser Input CallbacksProcess user input

glutKeyboardFunc( glutKeyboardFunc( keyboardkeyboard ); );void keyboard( unsigned char key, int x, int y ){ switch( key ) { case ‘q’ : case ‘Q’ : exit( EXIT_SUCCESS ); break;

case ‘r’ : case ‘R’ : rotate = GL_TRUE;

glutPostRedisplay(); break; }}

The mouse callbackThe mouse callback

glutMouseFunc(mymouse) void mymouse(GLint button, GLint state, GLint x, GLint y)void mymouse(GLint button, GLint state, GLint x, GLint y)

Returns – which button (GLUT_LEFT_BUTTON, GLUT_MIDDLE_BUTTON, GLUT_RIGHT_BUTTON) caused event

– state of that button (GLUT_UP, GLUT_DOWN)

– Position in window

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PositioningPositioningThe position in the screen window is usually measured in pixels with the origin at the top-left corner• Consequence of refresh done from top to

bottomOpenGL uses a world coordinate system with origin at the bottom left• Must invert y coordinate returned by

callback by height of window• y = h – y;

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(0,0) h

w

Orthographic ProjectionOrthographic Projection//myReshapevoid myReshape(int w, int h){ /* Save the new width and height */ screenWidth = w; screenHeight = h;

/* Reset the viewport... */ glViewport(0, 0, screenWidth, screenHeight);

glMatrixMode(GL_PROJECTION); glLoadIdentity(); glOrtho(0.0, (GLfloat)screenWidth, 0.0, (GLfloat)screenHeight, -1.0, 1.0); glMatrixMode(GL_MODELVIEW);

}

Rect DrawingRect Drawingvoid RenderScene(void)

{// Clear the window with current clearing colorglClear(GL_COLOR_BUFFER_BIT);

// Set current drawing color to red// R G BglColor3f(1.0f, 0.0f, 0.0f);

// Draw a filled rectangle with current colorglRectf(x, y, x + rsize, y - rsize);

// Flush drawing commands and swap glutSwapBuffers();

}

Time functionTime functionglutTimerFunc(unsigned int millis, void (GLUTCALLBACK *func)(int

value), int value);

Registers a timer callback to be triggered in a specified number of milliseconds.

BounceBouncevoid TimerFunction(int value) { // Reverse direction when you reach left or right edge if(x > windowWidth-rsize || x < -windowWidth) xstep = -xstep;

// Reverse direction when you reach top or bottom edge if(y > windowHeight || y < -windowHeight + rsize) ystep = -ystep;

// Actually move the square x += xstep; y += ystep;

// Check bounds. This is in case the window is made

// smaller while the rectangle is bouncing and the // rectangle suddenly finds itself outside the new // clipping volume if(x > (windowWidth-rsize + xstep)) x = windowWidth-rsize-1;

else if(x < -(windowWidth + xstep))x = -windowWidth -1;

if(y > (windowHeight + ystep)) y = windowHeight-1;

else if(y < -(windowHeight - rsize + ystep))y = -windowHeight + rsize - 1;

// Redraw the scene with new coordinates glutPostRedisplay(); glutTimerFunc(33,TimerFunction, 1); }