OpenGL 라이브러리

1. OpenGL 라이브러리

2. OpenGL 관련 사이트 및프로그래밍 실습 예제 http://www.opengl.org http://www.cs.utah.edu/~narobins/opengl.html

3. OpenGL Part 1. Introduction

4. Prerequisites • Event-driven programming 에 대한 이해 • C / C++ 언어 사용 능력 • Win32 Operating System • Visual Studio • & nothing…

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

6. You can use OpenGL, But… • OpenGL 을 이용하지 않아도 이것들을 충분히 할 수 있다. • DirectX Graphics component • Win32 GDI

7. 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

8. OpenGL solutions ( on win32 ) • 일반적으로 다음의 세 가지 선택 가능성이 있다. • Win32 API + OpenGL • MFC + OpenGL • GLUT + OpenGL → We’ll choose this !

9. 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

10. 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

11. OpenGL Part 2. First experience with OpenGL

12. Simplest OpenGL sample

13. 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; }

14. You’ll learn these, step by step • OpenGL+GLUT downloading & installation • Project generation & setup on Visual Studio • Basic template of the general GLUT program • Callback functions of the general GLUT program • OpenGL Basic

15. Step 1 : OpenGL + GLUT • OpenGL • You already have OpenGL dll on your Win32 system X:\WINDOWS\SYSTEM32\OpenGL32.dll • You also have OpenGL lib & header in your Visual Studio directory X:\…\VisualStudio\VC98\Lib\OpenGL32.lib X:\…\VisualStudio\VC98\Include\GL\gl.h

16. Step 1 : OpenGL + GLUT • GLUT • Perhaps, you don’t have GLUT library • You can download GLUT library at, http://reality.sgi.com/mjk/glut3/glut3.html • You should place the unzipped files at, X:\WINDOWS\SYSTEM32\glut32.dll X:\…\VisualStudio\VC98\Lib\glut32.lib X:\…\VisualStudio\VC98\Include\GL\glut.h

17. Step 2 : Project on VS • File / New / Projects / Win32 Console Application • Project / Settings / Link / Object&library modules append : opengl32.lib glu32.lib glut32.lib • Make new files & add those to the project & compile, link & so on …

18. Step 3 : GLUT template • Win32 API template • WinMain() • Message pump • Registers a Window class, including WndProc() • WndProc() receives & processes messages • GLUT template • main()  normal C program • glutMainLoop() • Registers some callback functions • Callback functions are called with some values

19. Step 3 : GLUT template • main() int main( int argc, char** argv ) { glutInit( &argc, argv ); initWindow(); initCallbackFunctions(); initMenu(); initOpenGL(); glutMainLoop(); }

20. Step 3 : GLUT template • initWindow() void initWindow() { glutInitWindowSize( 512, 512 ); glutInitWindowPosition( 0, 0 ); glutInitDisplayMode( GLUT_DOUBLE|GLUT_RGB|GLUT_DEPTH); glutCreateWindow( “Simple OpenGL sample" ); }

21. Step 3 : GLUT template • initCallbackFunctions() void initCallbackFunctions() { glutReshapeFunc( reshape ); glutDisplayFunc( display ); glutKeyboardFunc( keyboard ); glutMouseFunc( mouse ); // & many other callback functions can be added }

22. Step 3 : GLUT template • initMenu() void initMenu() { int h_submenu = glutCreateMenu( submenu ); int h_menu = glutCreateMenu( menu ); glutAddSubMenu( “submenu”, h_submenu ); glutAddMenuEntry( “exit”, 0 ); glutAttachMenu( GLUT_RIGHT_BUTTON ); }

23. Step 3 : GLUT template • initOpenGL() • Initialize lights, materials, etc. …

24. 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 !!! )

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

26. Step 4 : Callback functions • Display ( WM_PAINT ) void display() { // GLUT calls this function when, // window contents need to be re-drawn.. } • Related APIs • glutPostRedisplay() • glutSwapBuffers()

27. Step 4 : Callback functions • 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 }

28. Step 4 : Callback functions • 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 }

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

30. Step 4 : Callback functions • 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 }

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

32. 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 ?

33. GL_LINES GL_POLYGON GL_LINE_STRIP GL_LINE_LOOP GL_POINTS GL_TRIANGLES GL_QUADS GL_TRIANGLE_FAN GL_TRIANGLE_STRIP GL_QUAD_STRIP Step 5 : OpenGL Basic

34. Step 5 : OpenGL Basic • How to code ? void display() { glBegin( GL_xxxx ); glVertex3d( 0.0, 1.0, 0.0 ); // ... glVertex3d( -1.0, 1.0, 0.0 ); glEnd(); }

35. Step 5 : OpenGL Basic glVertex3fv( v ) Data Type Vector Number of components b - byte ub - unsigned byte s - short us - unsigned short i - int ui - unsigned int f - float d - double omit “v” for scalar form glVertex2f( x, y ) 2 - (x,y) 3 - (x,y,z) 4 - (x,y,z,w)

36. Step 5 : OpenGL Basic • 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...

37. Step 5 : OpenGL Basic • 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(); }

38. Step 5 : OpenGL Basic

39. Step 5 : OpenGL Basic

40. Step 5 : OpenGL Basic

41. Step 5 : OpenGL Basic • 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...

42. Step 5 : OpenGL Basic • 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

43. Step 5 : OpenGL Basic • 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();

44. Step 5 : OpenGL Basic • 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

45. Step 5 : OpenGL Basic • Camera analogy viewing volume camera model tripod

46. Step 5 : OpenGL Basic • 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

47. Step 5 : OpenGL Basic • 3D rendering pipeline

48. Step 5 : OpenGL Basic • 3D rendering pipeline • Seeing is believing : Projection http://www.xmission.com/~nate/tutors.html

49. Step 5 : OpenGL Basic • 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 transformations moving the model • Viewport transformations enlarge or reduce the physical film

50. Step 5 : OpenGL Basic • Transformation • Common senses about OpenGL transformation • Transformation = Matrix • Matrix multiplication = Matrix stack • Two matrix mode : Projection / Model-View • Common OpenGL commands about Matrices glMatrixMode( GL_PROJECTION|GL_MODELVIEW ); glLoadIdentity(); glPushMatrix(); glPopMatrix();