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CS 174 Sec 1 Elements of Computer G raphics

CS 174 Sec 1 Elements of Computer G raphics. TA Gianfranco Doretto. TA Office. Place: Boelter Hall 4428 Time: Monday 3:00 – 4:00 pm If you really cannot come during office hours, email me to schedule an appointment (my office is BH3811C) Email: doretto@cs.ucla.edu

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CS 174 Sec 1 Elements of Computer G raphics

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  1. CS 174 Sec 1 Elements of Computer Graphics TA Gianfranco Doretto Gianfranco Doretto - April 12, 2002

  2. TA Office • Place: Boelter Hall 4428 • Time: Monday 3:00 – 4:00 pm • If you really cannot come during office hours, email me to schedule an appointment (my office is BH3811C) • Email:doretto@cs.ucla.edu • Mailing-list:cs174.1@seas.ucla.edu Gianfranco Doretto - April 12, 2002

  3. Grading • Midterm: 20% • Final: 20% • Lab: 50% 3 Lab project to turn in April 25, May 15 (16?), June 6 • Class Participation 10% Gianfranco Doretto - April 12, 2002

  4. Lab Policies • All the labs in this course are to be done individually. You can discuss the theory with other students, but the implementation, debugging, etc. has to be done strictly on an individual basis, • Submit aREADMEfile with each lab, only if you are doing the extra credit stuff, or if you are doing something different from what is mentioned in the lab description handout. Also, mention what assumptions you have made to get your lab running, • Late labs will be accepted at 10% of your grade penalty for each day it is late, to a max of 50%.With this max penalty in effect, you are free to turn in your lab until the last day of the quarter. • Everyone in this class should sign a academic honesty policy form and return it to the TA in the recitation meeting. No grade will be given to student who has not signed this agreement. • Note: The students’ programs will be checked and compared each other. If it is found that someone is cheating, both of you will be reported. Gianfranco Doretto - April 12, 2002

  5. Laboratories • Get a SEASnet account if you do not have it yet (go to 2567BH) • Locations of the lab and hours, see:http://www.seas.ucla.edu/seasnet/Docs/labs.html Gianfranco Doretto - April 12, 2002

  6. Discussion Outline • Lab Algorithm • Lab FAQ • Unclear Material • Midterm/Final Sample Questions • Questions / Discussion • Anything helpful for your assignments Gianfranco Doretto - April 12, 2002

  7. What is OpenGL • Is a software interface to graphics hardware • Core OpenGL: 200 commands • OpenGL Utility Library: 50 commands • Is hardware-independent: don’t need to work through whatever windowing system controls of the particular hardware you’re using • You must build up your desired model from a small set of geometric primitives – points, lines, and polygons Gianfranco Doretto - April 12, 2002

  8. How OpenGL render an Image? • 4 steps • I] construct shapes from geometric primitives, thereby creating mathematical description of objects • II] arrange the objects in 3D space and select the desired vantage point for viewing the composed scene Gianfranco Doretto - April 12, 2002

  9. How OpenGL render an Image? • III] calculate the colors of all the objects (explicitly assigned, lighting conditions, passing texture, combination) • IV] convert the mathematical description of objects and their associated color information to pixels on the screen (rasterization) Gianfranco Doretto - April 12, 2002

  10. Example int main (int argc, char *argv[]) { //Inizializes a window on the screen glutInit(&argc, argv); glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB); glutInitWindowSize (250, 250); glutInitWindowPosition (100, 100); glutCreateWindow ("Example1"); init(); glutDisplayFunc(display); glutMainLoop(); return 0; } Gianfranco Doretto - April 12, 2002

  11. Example #include <GL/glut.h> #include <stdio.h> #include <stdlib.h> void init(void) { //estblishes what color the window will be cleared to glClearColor(0.0, 0.0, 0.0, 0.0); //initialize viewing values glMatrixMode (GL_PROJECTION); glLoadIdentity(); //specifies the coordinate system OpenGL assumes //as it draws the final image and how the //image gets mapped to the screen glOrtho(0.0,1.0,0.0,1.0,-1.0,1.0); } Gianfranco Doretto - April 12, 2002

  12. Example void display() { //once the clearing color is set, the window is cleared //to that color whenever glClear() is called glClear(GL_COLOR_BUFFER_BIT); //establishes what color to use for drawing objects (white) glColor3f(1.0,1.0,1.0); //define the object to be drawn (polygon) glBegin(GL_POLYGON); //define the polygon's corner //(x,y,z) coordinates, the polygon is on the z=0 plane glVertex3f(0.25,0.25,0.0); glVertex3f(0.75,0.25,0.0); glVertex3f(0.75,0.75,0.0); glVertex3f(0.25,0.75,0.0); glEnd(); Gianfranco Doretto - April 12, 2002

  13. Example glColor3f(1.0,0.0,0.0); //define the object to be drawn (line loop) glBegin(GL_LINE_LOOP); //define the polygon's corner //(x,y,z) coordinates, the polygon is on the z=0 plane glVertex3f(0.25,0.25,0.0); glVertex3f(0.75,0.25,0.0); glVertex3f(0.75,0.75,0.0); glVertex3f(0.25,0.75,0.0); glEnd(); //ensures that the drawing commands are actually executed //rather than stored in a buffer awaiting additional OpenGL commands glFlush(); } Gianfranco Doretto - April 12, 2002

  14. Command Syntax • Syntax observations (functions, constant, 3f suffix, glVertex2i(1,3);glVertex2f(1.0,3.0);) • glColor3f(1.0,0.0,0.0); • GLfloat color_array[]={1.0,0.0,0.0} • glColor3fv(color_array); Gianfranco Doretto - April 12, 2002

  15. Geometric Primitives • GL_POINTS • GL_LINES • GL_POLYGON • GL_TRIANGLES • GL_QUADS • GL_LINE_STRIP • GL_LINE_LOOP • GL_TRIANGLE_STRIP • GL_TRIANGLE_FAN • GL_QUAD_STRIP Gianfranco Doretto - April 12, 2002

  16. OpenGL as a State Machine • OpenGL is a state machine • You put it into various states that than remain in effect until you change them • Examples of state variables:color, current viewing, projection transformations, polygon drawing models, position and characteristics of light, material property of objects Gianfranco Doretto - April 12, 2002

  17. OpenGL-Related libraries • OpenGL have to use the underlying mechanisms of the windowing system • There are several libraries that allow you to simplify your programming tasks • I] GLU (OpenGL Utility Library) lower-level commands • II] WGL routines (Windows) provide the Windows to OpenGL interface • III] GLUT (OpenGL Utility Toolkit) is a window-system-independent toolkit, to hide the complexities of differing window system APIs Gianfranco Doretto - April 12, 2002

  18. Include Files • #include <GL/gl.h> needed for all applications • #include <GL/glu.h> for almost all applications is required • #include <windows.h> Microsoft Windows require this (not recommended) • #include <GL/glut.h> if you are using GLUT for managing your window manager tasks (NOTE: include glut.h and do not include gl.h and glu.h for portability) Gianfranco Doretto - April 12, 2002

  19. GLUT, the OpenGL Utility Toolkit • OpenGL is window system or operating system independent • It contains no command for opening window or reading events from the keyboard or mouse. GLUT gives you these missing commands • GLUT includes also several routines that create “complicated” 3D objects (glutSolidSphare(); glutSolidCone(); glutSolidTeapot(); glutWireTorus(); …) (NOTE: also GLU has something) Gianfranco Doretto - April 12, 2002

  20. GLUT Window Management • glutInit(int *argc, char **argv)initializes GLUT and processes any command line arguments. Should be called before any other GLUT routine • glutInitDisplayMode(unsigned int mode) specify RGBA or color-index color model; single- or double-buffer; depth buffer; Gianfranco Doretto - April 12, 2002

  21. GLUT Window Management • glutInitWindowPosition(int x, int y) specifies the screen location for the upper-left corner of your window • glutWindowSize(int width, int size) specifies the size, in pixels, of your window • glutCreateWindow(char *string) creates a window with an OpenGL context (NOTE:until glutMainLoop() is called, the window is not yet displayed Gianfranco Doretto - April 12, 2002

  22. The Display Callback • glutDisplayFunc(void(*func)(void)) is the first and most important callback function • Whenever GLUT determines that the contents of the window need to be redisplayed, the callback function above is executed • You should put all the routines you need to redraw the scene in the display callback function Gianfranco Doretto - April 12, 2002

  23. Running the Program • The very last thing you must do is call glutMainLoop(void) • All windows that have been created are now shown, and rendering to those windows is now effective • Once this loop is entered, it is never exited! Gianfranco Doretto - April 12, 2002

  24. Handling Input Events • Routines to register callback commands that are invoked when specified events occur • glutReshapeFunc(void (*func)(int w,int h)) indicates what action should be taken when the window is resized Gianfranco Doretto - April 12, 2002

  25. Handling Input Events • glutKeyboardFunc(void (*func) (unsigned char key, int x, int y)) and glutMouseFunc(void (*func) (int button, int int state, int x, int y))allow you to link a keyboard key or a mouse button with a routine that’s invoked when the key or mouse button is pressed or released Gianfranco Doretto - April 12, 2002

  26. Handling Input Events • glutMotionFunc(void(*func)(int x,int y)) registers a routine to call back when the mouse is moved while a mouse button is also pressed Gianfranco Doretto - April 12, 2002

  27. Managing a background Process • You can specify a function that’s to be executed if no other events are pending • glutIdleFunc(void(*func)(void)) this routine takes a pointer to the function as its only argument Gianfranco Doretto - April 12, 2002

  28. Skeleton code • Download skeleton.tar.gz to your SEAsnet Account • Exact file by:     gunzip skeleton.tar.gz tar -xvf skeleton.tar • Change directory to skeleton by: cd skeleton • Compile the sample code by:    make Gianfranco Doretto - April 12, 2002

  29. Unix Basic Commands • emacs emacs editor • mkdir create a directory • cd change directory • ls list of files • cp copy • mv move and rename files • rm delete files • chmod change access to the files Gianfranco Doretto - April 12, 2002

  30. Compiling Under Linux/Solaris (Makefile) gcc -o Example Example.c -lX11 -lGL -lGLU -lglut –lm Under Windows (not recommended!) These libraries must be compiled • Opengl32.lib • Glu32.lib Gianfranco Doretto - April 12, 2002

  31. Working without UNIX • From Seas Labs: • do editing with VC++ • ftp to ugrad.seas.ucla.edu • Use Exceed3D to show graphics output • From Home: • do editing with VC++ • ftp to ugrad.seas.ucla.edu • Use XWin32 to show graphics output (trial version downloadable at http://www.starnet.com/products/) • Install your own linux system. Contact the Linux user group for help http://ww.linux.ucla.edu (Linux user group) Gianfranco Doretto - April 12, 2002

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