Intro to OpenGL (Version 2)

1. Intro to OpenGL (Version 2) Geb Thomas

2. Setting Up GLUT • You will need GLUT for opening windows • We can use the version made by Nate Robins: • http://www.xmission.com/~nate/glut.html • Download the .zip file, unzip it and store it in a convenient directory on your drive • I stored everything in h:/documents/glut

3. Setting up the Compiler • You need to tell the compiler where the header file is. One way is instead of using #include <glut.h>, which assumes that the glut header file is in a standard location, you can use #include “h:/documents/glut/glut.h”. Then the compiler will look at this location. • An easy way to handle the .dll file is to copy it to the location of your executable file, perhaps: • H:\testProgram\debug

4. Setting up a Window with GLUT • Learn about glut here: http://www.opengl.org/developers/documentation/glut/spec3/spec3.html • glutInit(argc, argv); /* initialize glut */ • glutInitWindowSize(int width, int height); • /* set the window size. 300x300 by default */ • glutInitWindowPosition(x, y); • /* set the window position, default –1, -1, which means let the operating system decide */

5. glutInitDisplayMode • Use glutInitDisplayMode( GLUT_RGBA | GLUT_SINGLE | GLUT_DEPTH ) • Provides RGB color rather than indexed color • A single frame buffer, rather than double buffering • A depth buffer

6. Opening a Window • int glutCreateWindow(char *name); • Returns an integer identifier for the window • No drawing is effective until glutMainLoop • Several windows or subwindows may be opened. • Windows may be resized or repositioned • Window and display modes are system states that may be set and queried

7. The Main Loop • Glut allows you to define callbacks: • void glutDisplayFunc(void (*func)(void)); • void glutReshapeFunc(void (*func)(int width, int height)); • void glutKeyboardFunc(void (*func)(unsigned char key, int x, int y)); • void glutMouseFunc(void (*func)(int button, int state, int x, int y)); • void glutMainLoop(void);

8. Working with OpenGL • Get information from here (as well as other sources) • http://ask.ii.uib.no/ebt-bin/nph-dweb/dynaweb/SGI_Developer/OpenGL_PG/

9. Clearing the Window • To clear the color to black (in RGBA mode) • glClearColor(0.0, 0.0, 0.0, 0.0); • glClear(GL_COLOR_BUFFER_BIT); • To also clear the depth buffer you might use: • glClearColor(0.0, 0.0, 0.0, 0.0); • glClearDepth(1.0); • glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

10. Drawing Colors • The current drawing color is a state. Change the state with glColor3f commands such as: • glColor3f(0.0, 0.0, 0.0); // black • glColor3f(1.0, 0.0, 0.0); //red • glColor3f(0.0, 1.0, 0.0); //green • glColor3f(1.0, 1.0, 0.0); //yellow • glColor3f(0.0, 0.0, 1.0); //blue • glColor3f(1.0, 0.0, 1.0); //magenta • glColor3f(0.0, 1.0, 1.0); //cyan • glColor3f(1.0, 1.0, 1.0); //white

11. Flushing the Buffers • void glFlush(void); • Sends a command to flush out the pipeline and finish the drawing • void glFinish(void); • Waits until drawing is completed, then returns

12. Setting up a Coordinate Frame • void reshape (int w, int h) { • glViewport (0, 0, (GLsizei) w, (GLsizei) h); • glMatrixMode (GL_PROJECTION); • glLoadIdentity (); • gluOrtho2D (0.0, (GLdouble) w, 0.0, (GLdouble) h); • }