OpenGL 라이브러리. OpenGL 관련 사이트 및 프로그래밍 실습 예제 narobins/opengl.html

OpenGL 라이브러리

OpenGL 관련 사이트 및프로그래밍 실습 예제

http://www.opengl.org

http://www.cs.utah.edu/~narobins/opengl.html

OpenGL

Part 1.Introduction

Prerequisites

Event-driven programming 에 대한 이해 C / C++ 언어 사용 능력

Win32 Operating System Visual Studio

& nothing…

What do I want to do ?

Ex) 2 차원 그래픽 드로잉 프로그램을 만들고 싶다 .

Mouse, keyboard, menu 등을 통한 interaction

기본적인 drawing primitive 들 제공

간단한 animation 기능 제공

You can use OpenGL, But…

OpenGL 을 이용하지 않아도 이것들을 충분히 할 수 있다 .

DirectX Graphics component

Win32 GDI

Then, why OpenGL ?

OpenGL 을 이용하면 이것보다 훨씬 더 많은 것들을 할 수 있다 .

OpenGL = 3D graphics rendering API

But, DirectX Graphics ≈ OpenGL ?

OpenGL = window system independent API

OpenGL = operating system independent API

OpenGL solutions ( on win32 )

일반적으로 다음의 세 가지 선택 가능성이 있다 .

Win32 API + OpenGL

MFC + OpenGL

GLUT + OpenGL → We’ll choose this !

What is GLUT ?

Mark J. Kilgard 가 개발한 portable windowing API

대부분의 window system 에 보편적인 기능들을 wrapping 한 상위 interface 를 제공

Win32 를 비롯한 많은 window system 에 대해 implementation 이 이루어져 있음

OpenGL 이 제공하는 범위보다 상위 수준의 utility function 들도 제공함

Then, why GLUT ?

Pros Window system independent code

→ UNIX / X-window 에서 개발된 수많은 code 들을 그대로 재사용할 수 있다 .

매우 쓰기 쉽다→ Win32 API 도 , MFC 도 , Xlib 도 전혀 알 필요 없다 .

Cons Window system 의 기능을 제한적으로 이용 가능

OpenGL

Part 2.First experience with OpenGL

Simplest OpenGL sample

Simplest OpenGL sample

#include <GL/glut.h>void display(){

glClear( GL_COLOR_BUFFER_BIT );glBegin( GL_TRIANGLES );

glColor3f( 1.0f, 1.0f, 1.0f );glVertex2f( -0.8f, -0.5f );glVertex2f( 0.0f, 0.8f );glVertex2f( 0.8f, -0.5f );

glEnd();glFlush();

}int main(int argc, char** argv){

glutInit( &argc, argv );glutCreateWindow( "Simplest OpenGL sample" );glutDisplayFunc( display );glutMainLoop();return 0;

}

You’ll learn these, step by step

1) OpenGL+GLUT downloading & installation

2) Project generation & setup on Visual Studio

3) Basic template of the general GLUT program

4) Callback functions of the general GLUT program

5) OpenGL Basic

Step 1 : OpenGL + GLUT

OpenGL

1) You already have OpenGL dll on your Win32 systemX:\WINDOWS\SYSTEM32\OpenGL32.dll

2) You also have OpenGL lib & header in your Visual Studio directoryX:\…\VisualStudio\VC98\Lib\OpenGL32.lib

X:\…\VisualStudio\VC98\Include\GL\gl.h

Step 1 : OpenGL + GLUT

GLUT

1) Perhaps, you don’t have GLUT library

2) You can download GLUT library at,

http://reality.sgi.com/mjk/glut3/glut3.html

3) You should place the unzipped files at,X:\WINDOWS\SYSTEM32\glut32.dllX:\…\VisualStudio\VC98\Lib\glut32.libX:\…\VisualStudio\VC98\Include\GL\glut.h

Step 2 : Project on VS

1) File / New / Projects / Win32 Console Application

2) Project / Settings / Link / Object&library modulesappend : opengl32.lib glu32.lib glut32.lib

Make new files & add those to the project & compile, link& so on …

Step 3 : GLUT template

Win32 API template1) WinMain()

2) Message pump

3) Registers a Window class, including WndProc()

4) WndProc() receives & processes messages

GLUT template1) main() normal C program

2) glutMainLoop()

3) Registers some callback functions

4) Callback functions are called with some values


main()

int main( int argc, char** argv ){

glutInit( &argc, argv );initWindow();initCallbackFunctions();initMenu();initOpenGL();glutMainLoop();

}


initWindow()

void initWindow()

{

glutInitWindowSize( 512, 512 );

glutInitWindowPosition( 0, 0 );

glutInitDisplayMode(

GLUT_DOUBLE|GLUT_RGB|GLUT_DEPTH);

glutCreateWindow( “Simple OpenGL sample" );

}


initCallbackFunctions()

void initCallbackFunctions()

{

glutReshapeFunc( reshape );

glutDisplayFunc( display );

glutKeyboardFunc( keyboard );

glutMouseFunc( mouse );

// & many other callback functions can be added

}


initMenu()

void initMenu()

{

int h_submenu = glutCreateMenu( submenu );

int h_menu = glutCreateMenu( menu );

glutAddSubMenu( “submenu”, h_submenu );

glutAddMenuEntry( “exit”, 0 );

glutAttachMenu( GLUT_RIGHT_BUTTON );

}


initOpenGL()

Initialize lights, materials, etc. …

Step 4 : Callback functions

Frequently used callback functions

void reshape( int w, int h );void display();void keyboard( unsigned char key, int x, int

y );void mouse( int btn, int state, int x, int y );void timer( int timer_id );void menu( int value );void idle();

( You should refer to the GLUT API spec !!! )


Reshape ( WM_SIZE )

void reshape( int w, int h )

{

// GLUT calls this function when,

// window size has changed..

// - w : window width

// - h : window height

}


Display ( WM_PAINT )

void display(){

// GLUT calls this function when,// window contents need to be re-drawn..

}

Related APIs glutPostRedisplay() glutSwapBuffers()


Keyboard ( WM_KEYDOWN )

void keyboard( unsigned char key, int x, int y )

{


// user presses keyboard..

// - key : ASCII character code

// - x, y : mouse location when key is pressed

}


Mouse ( WM_[ L/R ]BUTTON[ DOWN/UP ] )

void mouse( int button, int state, int x, int y )

{


// user presses or releases mouse buttons..

// - button : GLUT_[ RIGHT/MIDDLE/LEFT ]_BUTTON

// - state : GLUT_DOWN | GLUT_UP

// - x, y : mouse location when the state changed

}


Timer ( WM_TIMER )

void timer( int value )

{


// the registered timer has expired..

// - value : registered timer ID

}

glutTimerFunc( unsigned int msecs, void (*func)(int value), int value )


Menu ( WM_COMMAND )

void menu( int value )

{


// a menu entry is selected from the menu..

// - value : selected menu entry’s ID

}


Idle ( PeekMessage(...)==0 )

void idle()

{


// it doesn’t have nothing to do..

}

Step 5 : OpenGL Basic

Drawing Primitives

You can draw “ready-made” primitives which OpenGL provides

In fact, you only gives “vertices” to OpenGL

& inform that “what the vertices compose”

Then, what kind of “Primitive” s ?


GL_QUAD_STRIPGL_QUAD_STRIP

GL_POLYGONGL_POLYGON

GL_TRIANGLE_STRIPGL_TRIANGLE_STRIP GL_TRIANGLE_FANGL_TRIANGLE_FAN

GL_POINTSGL_POINTS

GL_LINESGL_LINES

GL_LINE_LOOPGL_LINE_LOOPGL_LINE_STRIPGL_LINE_STRIP

GL_TRIANGLESGL_TRIANGLES

GL_QUADSGL_QUADS


How to code ?

void display(){

glBegin( GL_xxxx );glVertex3d( 0.0, 1.0, 0.0 );// ...glVertex3d( -1.0, 1.0, 0.0 );glEnd();

}


glVertex3fv( glVertex3fv( 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 )


But, I want to

control the shape of the primitive( points ? lines ? or fill ? )

control the size of the point ( or vertices ) control the width of the line control the color of the filling & much more, much more...

You should know this !

OpenGL is a State Machine...


Then, how to code ?

void display(){

glBegin( GL_XXXX );glColor3d( 1.0, 0.0, 0.0 );glVertex3d( 0.0, 0.0, 0.0 );// ...glColor3d( 0.0, 0.0, 1.0 );glVertex3d( -1.0, 1.0, 0.0 );glEnd();

}





Is that all ?

Complie, and link, and execute... Of course, nothing appears...

Why ?

Where do I draw them ? You should know some OpenGL buffers ! Color buffer, Depth buffer, and Double buffering...


OpenGL Buffers

Color buffer ; stores color values, to appear in screen

Depth buffer ; stores depth values, to accomplish hidden surface removal

Double buffering ; front & back buffer, chaining, to accomplish flicker-free animation


So, how to code ? Remember the function initWindow()

glutInitDisplayMode( GLUT_RGB|GLUT_DEPTH|

GLUT_DOUBLE );

Then, insert & append next 2 lines in display()glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);// ...from glBegin() to glEnd()...glutSwapBuffers();


We did it !!! but...

Resizing, minimizing or maximizing window makes the image ugly...

Why ?

You should remember that OpenGL is a 3D API, not 2D

It means, you don’t draw directly on the window Rather, a camera takes a picture of the 3D space


Camera analogy

camera

tripod model

viewingvolume


3D rendering pipeline

We’ll play with 2D objects for a while

But, OpenGL is a 3D rendering API in itself, never a 2D drawing API

You’ll learn the complete 3D rendering pipeline in on-going class

At now, I’ll introduce it very simply, so you can understand some OpenGL commands





Seeing is believing : Projection

http://www.xmission.com/~nate/tutors.html


Camera analogy & Transformations Projection transformations

adjust the lens of the camera Viewing transformations

tripod–define position and orientation of the viewing volume in the world

Modeling transformationsmoving the model

Viewport transformationsenlarge or reduce the physical film


Transformation

Common senses about OpenGL transformation Transformation = Matrix Matrix multiplication = Matrix stack Two matrix mode : Projection / Model-View

Common OpenGL commands about MatricesglMatrixMode( GL_PROJECTION|GL_MODELVIEW );glLoadIdentity();glPushMatrix();glPopMatrix();


Projection Transformation

Orthographic projection Adequate for our 2D examplesglOrtho( left, right, bottom, top, near,

far );

gluOrtho2D( left, right, bottom, top );

Perspective projection Adequate for realistic 3D examplesglFrustum( left, right, bottom, top, near,

far );

gluPerspective( fovy, aspect, near, far );


Question ?

We’ve got a little understanding of “ 3D rendering pipeline ”

Then, how can we solve the previous image “disappearance” & “distortion” problem ?

Hint : reshape() callback function


Answer !

void reshape( int w, int h ){

// next line solves “disappearance” problem

glViewport( 0, 0, w, h );

glMatrixMode( GL_PROJECTION );glLoadIdentity();glOrtho( -w/2, w/2, -h/2, h/2, -1, 1);

}

Reference

Documents

OpenGL 라이브러리. OpenGL 관련 사이트 및 프로그래밍 실습 예제 narobins/opengl.html