Open GL http www opengl org http www

Open. GL 관련 사이트 및 프로그래밍 실습 예제 http: //www. opengl. org http: //www. cs. utah. edu/~narobins/opengl. html

Open. GL Part 1. Introduction

Prerequisites Event-driven programming 에 대한 이해 ã C / C++ 언어 사용 능력 ã Win 32 Operating System ã Visual Studio ã ã & nothing…

What do I want to do ? ã Ex) 2차원 그래픽 드로잉 프로그램을 만들고 싶 다. Ý Mouse, keyboard, menu 등을 통한 interaction Ý 기본적인 drawing primitive 들 제공 Ý 간단한 animation 기능 제공

You can use Open. GL, But… ã Open. GL 을 이용하지 않아도 이것들을 충분히 할 수 있다. Ý Direct. X Graphics component Ý Win 32 GDI

Then, why Open. GL ? ã Open. GL 을 이용하면 이것보다 훨씬 더 많은 것 들을 할 수 있다. Ý Open. GL = 3 D graphics rendering API Ý But, Direct. X Graphics ≈ Open. GL ? Ý Open. GL = window system independent API Ý Open. GL = operating system independent API

Open. GL solutions ( on win 32 ) ã 일반적으로 다음의 세 가지 선택 가능성이 있다. Ý Win 32 API + Open. GL Ý MFC + Open. GL Ý GLUT + Open. GL → We’ll choose this !

What is GLUT ? ã Mark J. Kilgard 가 개발한 portable windowing API Ý 대부분의 window system 에 보편적인 기능들을 wrapping 한 상위 interface 를 제공 Ý Win 32 를 비롯한 많은 window system 에 대해 implementation 이 이루어져 있음 Ý Open. GL 이 제공하는 범위보다 상위 수준의 utility function 들도 제공함

Open. GL Part 2. First experience with Open. GL

Simplest Open. GL sample

Simplest Open. GL sample #include <GL/glut. h> void display() { gl. Clear( GL_COLOR_BUFFER_BIT ); gl. Begin( GL_TRIANGLES ); gl. Color 3 f( 1. 0 f, 1. 0 f ); gl. Vertex 2 f( -0. 8 f, -0. 5 f ); gl. Vertex 2 f( 0. 0 f, 0. 8 f ); gl. Vertex 2 f( 0. 8 f, -0. 5 f ); gl. End(); gl. Flush(); } int main(int argc, char** argv) { glut. Init( &argc, argv ); glut. Create. Window( "Simplest Open. GL sample" ); glut. Display. Func( display ); glut. Main. Loop(); return 0; }

You’ll learn these, step by step 1) 2) 3) 4) 5) Open. GL+GLUT downloading & installation Project generation & setup on Visual Studio Basic template of the general GLUT program Callback functions of the general GLUT program Open. GL Basic

Step 1 : Open. GL + GLUT q Open. GL 1) You already have Open. GL dll on your Win 32 system X: WINDOWSSYSTEM 32Open. GL 32. dll 2) You also have Open. GL lib & header in your Visual Studio directory X: …Visual. StudioVC 98LibOpen. GL 32. lib X: …Visual. StudioVC 98IncludeGLgl. h

Step 1 : Open. GL + GLUT q GLUT 1) Perhaps, you don’t have GLUT library 2) You can download GLUT library at, http: //reality. sgi. com/mjk/glut 3. h tml 3) You should place the unzipped files at, X: WINDOWSSYSTEM 32glut 32. dll X: …Visual. StudioVC 98Libglut 32. lib X: …Visual. StudioVC 98IncludeGLglut. h

Step 2 : Project on VS 1) File / New / Projects / Win 32 Console Application 2) Project / Settings / Link / Object&library modules append : opengl 32. lib glut 32. lib ã Make new files & add those to the project & compile, link & so on …

Step 3 : GLUT template q Win 32 API template Win. Main() 2) Message pump 3) Registers a Window class, including Wnd. Proc() 4) Wnd. Proc() receives & processes messages 1) q GLUT template main() normal C program 2) glut. Main. Loop() 3) Registers some callback functions 4) Callback functions are called with some values 1)

Step 3 : GLUT template q main() int main( int argc, char** argv ) { glut. Init( &argc, argv ); init. Window(); init. Callback. Functions(); init. Menu(); init. Open. GL(); glut. Main. Loop(); }

Step 3 : GLUT template q init. Window() void init. Window() { glut. Init. Window. Size( 512, 512 ); glut. Init. Window. Position( 0, 0 ); glut. Init. Display. Mode( GLUT_DOUBLE|GLUT_RGB|GLUT_DEPTH); glut. Create. Window( “Simple Open. GL sample" ); }

Step 3 : GLUT template q init. Callback. Functions() void init. Callback. Functions() { glut. Reshape. Func( reshape ); glut. Display. Func( display ); glut. Keyboard. Func( keyboard ); glut. Mouse. Func( mouse ); // & many other callback functions can be added }

Step 3 : GLUT template q init. Menu() void init. Menu() { int h_submenu = glut. Create. Menu( submenu ); int h_menu = glut. Create. Menu( menu ); glut. Add. Sub. Menu( “submenu”, h_submenu ); glut. Add. Menu. Entry( “exit”, 0 ); glut. Attach. Menu( GLUT_RIGHT_BUTTON ); }

Step 3 : GLUT template q init. Open. GL() ü Initialize lights, materials, etc. …

Step 4 : Callback functions q 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 !!! )

Step 4 : Callback functions q Reshape ( WM_SIZE ) void { // // } reshape( int w, int h ) GLUT calls this function when, window size has changed. . - w : window width - h : window height

Step 4 : Callback functions q Display ( WM_PAINT ) void display() { // GLUT calls this function when, // window contents need to be re-drawn. . } q Related APIs glut. Post. Redisplay() ü glut. Swap. Buffers() ü

Step 4 : Callback functions q Keyboard ( WM_KEYDOWN ) void keyboard( unsigned char key, int x, int y ) { // GLUT calls this function when, // user presses keyboard. . // - key : ASCII character code // - x, y : mouse location when key is pressed }

Step 4 : Callback functions q Mouse ( WM_[ L/R ]BUTTON[ DOWN/UP ] ) void mouse( int button, int state, int x, int y ) { // GLUT calls this function when, // 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 }

Step 4 : Callback functions q Timer ( WM_TIMER ) void timer( int value ) { // GLUT calls this function when, // the registered timer has expired. . // - value : registered timer ID } ü glut. Timer. Func( unsigned int msecs, void (*func)(int value), int value )

Step 4 : Callback functions q Menu ( WM_COMMAND ) void menu( int value ) { // GLUT calls this function when, // a menu entry is selected from the menu. . // - value : selected menu entry’s ID }

Step 4 : Callback functions q Idle ( Peek. Message(. . . )==0 ) void idle() { // GLUT calls this function when, // it doesn’t have nothing to do. . }

Step 5 : Open. GL Basic q Drawing Primitives ü You can draw “ready-made” primitives which Open. GL provides ü In fact, you only gives “vertices” to Open. GL ü & inform that “what the vertices compose” ü Then, what kind of “Primitive” s ?

Step 5 : Open. GL Basic GL_LINES GL_LINE_STRIP GL_POINTS GL_LINE_LOOP GL_POLYGON GL_TRIANGLES GL_QUAD_STRIP GL_TRIANGLE_FAN

Step 5 : Open. GL Basic q How to code ? void display() { gl. Begin( GL_xxxx ); gl. Vertex 3 d( 0. 0, 1. 0, 0. 0 ); //. . . gl. Vertex 3 d( -1. 0, 0. 0 ); gl. End(); }

Step 5 : Open. GL Basic gl. Vertex 3 fv( v ) Number of components 2 3 4 - (x, y) (x, y, z, w) Data Type b ub s us i ui f d - byte unsigned byte short unsigned short int unsigned int float double Vector omit “v” for scalar form gl. Vertex 2 f( x, y )

Step 5 : Open. GL Basic q But, I want to ü control the shape of the primitive ( points ? lines ? or fill ? ) ü control the size of the point ( or vertices ) control the width of the line control the color of the filling & much more, much more. . . ü ü ü q You should know this ! ü Open. GL is a State Machine. . .

Step 5 : Open. GL Basic q Then, how to code ? void display() { gl. Begin( GL_XXXX ); gl. Color 3 d( 1. 0, 0. 0 ); gl. Vertex 3 d( 0. 0, 0. 0 ); //. . . gl. Color 3 d( 0. 0, 1. 0 ); gl. Vertex 3 d( -1. 0, 0. 0 ); gl. End(); }

Step 5 : Open. GL Basic

Step 5 : Open. GL Basic

Step 5 : Open. GL Basic

Step 5 : Open. GL Basic q Is that all ? ü ü q Complie, and link, and execute. . . Of course, nothing appears. . . Why ? ü ü ü Where do I draw them ? You should know some Open. GL buffers ! Color buffer, Depth buffer, and Double buffering. . .

Step 5 : Open. GL Basic q Open. GL Buffers ü Color buffer ; stores color values, to appear in screen ü Depth buffer ; stores depth values, to accomplish hidden surface removal ü Double buffering ; front & back buffer, chaining, to accomplish flicker-free animation

Step 5 : Open. GL Basic q So, how to code ? ü Remember the function init. Window() glut. Init. Display. Mode( GLUT_RGB|GLUT_DEPTH|GLUT_DOUBLE ); ü Then, insert & append next 2 lines in display() gl. Clear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUF FER_BIT); //. . . from gl. Begin() to gl. End(). . . glut. Swap. Buffers();

Step 5 : Open. GL Basic q We did it !!! but. . . ü q Resizing, minimizing or maximizing window makes the image ugly. . . Why ? ü ü ü You should remember that Open. GL is a 3 D API, not 2 D It means, you don’t draw directly on the window Rather, a camera takes a picture of the 3 D space

Step 5 : Open. GL Basic q Camera analogy viewing volume camera tripod model

Step 5 : Open. GL Basic q 3 D rendering pipeline ü We’ll play with 2 D objects for a while ü But, Open. GL is a 3 D rendering API in itself, never a 2 D drawing API ü You’ll learn the complete 3 D rendering pipeline in on-going class ü At now, I’ll introduce it very simply, so you can understand some Open. GL commands

Step 5 : Open. GL Basic q 3 D rendering pipeline

Step 5 : Open. GL Basic q 3 D rendering pipeline ü Seeing is believing : Projection http: //www. xmission. com/~nate/tutors. htm l

Step 5 : Open. GL Basic q Camera analogy & Transformations q Projection transformations adjust the lens of the camera q Viewing transformations tripod–define position and orientation of the viewing volume in the world q Modeling transformations moving the model q Viewport transformations enlarge or reduce the physical film

Step 5 : Open. GL Basic q Transformation q Common senses about Open. GL transformation Transformation = Matrix ü Matrix multiplication = Matrix stack ü Two matrix mode : Projection / Model-View ü q Common Open. GL commands about Matrices gl. Matrix. Mode( GL_PROJECTION|GL_MODELVIEW ); gl. Load. Identity(); gl. Push. Matrix(); gl. Pop. Matrix();

Step 5 : Open. GL Basic q Projection Transformation q Orthographic projection Adequate for our 2 D examples gl. Ortho( left, right, bottom, top, near, far ); glu. Ortho 2 D( left, right, bottom, top ); ü q Perspective projection Adequate for realistic 3 D examples gl. Frustum( left, right, bottom, top, near, far ); glu. Perspective( fovy, aspect, near, far ); ü

Step 5 : Open. GL Basic q Question ? q We’ve got a little understanding of “ 3 D rendering pipeline ” q Then, how can we solve the previous image “disappearance” & “distortion” problem ? q Hint : reshape() callback function

Step 5 : Open. GL Basic q Answer ! void reshape( int w, int h ) { // next line solves “disappearance” problem gl. Viewport( 0, 0, w, h ); gl. Matrix. Mode( GL_PROJECTION ); gl. Load. Identity(); gl. Ortho( -w/2, -h/2, -1, 1); }

Reference