1. Introduction 2. Line Drawing 3. Drawing Objects 4. More Drawing Tools 5. Normal Vectors and Polygonal Models of Surfaces 6. Viewing I -- Affine Transformations 7. Viewing II -- Projections

8. Color 9. Lighting 10. Blending, antialiasing, fog .. 11. Display Lists, Bitmaps and Images 12. Texture Mapping 13. Curves and Surfaces 14. Games and SDL

Introduction

1. Applications of Computer Graphics
   Computer Graphics and Image Processing The fields of computer graphics and image procesing are blending together more each year.

   Computer Graphics -- create pictures and images, synthesize them on the basis of some description, or model in a computer

   Image Processing -- improve or alter images that were created elsewhere

   
   
   Art, Entertainment, and publishing
   movie production, animation, special effects
   computer games
   browsing on the World Wide Web
   slide, book, and magazine design
   
   
   Monitoring a Process
   
   
   
   Displaying Simulations
   e.g. virtual reality
   
   
   
   Computer-aided Design
   e.g. Computer-aided Architectural Design, Electrical Circuit Design
   
   
   Scientific Analysis and Visualization
   presenting scientific information in the right way let you gain new insights into the investigating process
   

   Digital shape sampling and processing (DSSP)

   DSSP describes the ability to use scanning hardware and processing software to digitally capture physical objects and automatically create accurate 3D models with associated structural properties for design, engineering, inspection and custom manufacturing. What digital signal processing (DSP) is to audio, DSSP is to 3D geometry.

   see http://www.geomagic.com/news/articles/dssppart1.php3

   
   
2. What is OpenGL?
   Application programming interface ( API )
   a collection of routines that the programmer can call, along with a model of how the routines work together to produce graphics
   250 distinct commands ( about 200 core, 50 utility )  
   
   
   Device-independent graphics programming

   • produce nearly identical outputs in various hardware platforms
   • no user-input commands in core
   • no high-level commands for 3-D objects, one must build model from primitives -- points, lines, and polygons
   • OpenGL Utility Library ( GLU ) provides many modeling features,
   
   
3. Basics of OpenGL Code
   Rendering -- the process by which a computer creates images from models.
   Models or objects are constructed from geometric primitives like points, lines, polylines, polygons which are defined by one or more vertices.
   Functions calls between glBegin() and glEnd()
   Example -- drawing 3 points

   	glBegin( GL_POINTS );
   	  glVertex2i( 100, 40 );
   	  glVertex2i( 120, 50 );
   	  glVertex2i( 140, 80 );
   	glEnd();
   	

   glVertex2i(...)
   gl gl library	Vertex basic command	2 number of arguments	i type of arguments

   
   
   Data Types:
   

   Suffix	Data Type	Corresponding   C type	OpenGL Type   Deinfition
   b	8-bit Integer	signed char	GLbyte
   s	16-bit Integer	short	GLshort
   i	32-bit Integer	int or long	GLint, GLsizei
   f	32-bit Floating-point	float	GLfloat, GLclampf
   d	64-bit Integer	double	GLdouble, GLclampd
   ub	8-bit Unsigned Integer	unsigned char	GLubyte, GLboolean
   us	16-bit Unsigned Integer	signed short	GLushort
   ui	32-bit Unsigned Integer	unsigned int or unsigned long	GLuint, GLenum, GLbitfield

   glVertex2i ( 7, 11 );
   glVertex2f ( 7.0, 11.0 );
   are the same

   
   
   Number of Arguments: 2, 3, 4
   
   
   Formats:

   • 'v' indicates vector format
   • absence of 'v' indicates scalar format
     
   • Example: glColor3f( 1.0, 0.0, 0.0 );
     
     GLfloat color_array[] = {1.0, 0.0, 0.0};
     glColor3fv( color_array );
   
   
4. The Event Loop
   • OpenGL programs often run in an event loop.
   • After initialization, the program falls into an infinite loop accepting and handling events, like displaying, mouse movement, window reshaping ..
   
   
5. OpenGL as a State Machine
   • OpenGL can be viewed as a state machine.
   • state variables: color, line width, line stipple pattern, shading method, object positions ...
   • On-Off state variables can be set to GL_FALSE ( off ) or GL_TRUE ( on )
     glEnable ( .. ),       glDisable( .. )
     GL_LINE_SMOOTH -- if enabled draw lines with correct filtering, otherwise draw lines with aliasing
   • Mode state variables require command specific to the state variable in order to change it
     e.g. glShadeModel ( GL_SMOOTH ) -- smooth shading
         glShadeModel ( GL_FLAT ) -- flat shading ( default )
   • Value state variables require command specific to the state variable in order to change it
     e.g. glColor3f( 0.5, 0.5, 0.5 )
     
     
   • Query current state At any point, the programmer can query the system for any variable's current value. Typically, one of the four following commands is used glGetBooleanv(), glGetDoublev(), glGetFloatv(), or glGetIntegerv()
   • Save current state in stack A collection of state variables can be saved on an attribute stack.
     glPushAttrib()
     glPopAttrib()
   
   
6. Demo Programs
   • Simple Drawing
     

     //draw.cpp : demo program for drawing 3 dots, two lines, ploylines, rectangles #include <GL/glut.h> //initialization void init( void ) { glClearColor( 1.0, 1.0, 1.0, 0.0 ); //get white background color glColor3f( 0.0f, 0.0f, 0.0f ); //set drawing color glPointSize( 4.0 ); //a dot is 4x4 glMatrixMode( GL_PROJECTION ); glLoadIdentity(); //replace current matrix with identity matrix gluOrtho2D( 0.0, 500.0, 0.0, 500.0 ); } void display( void ) { glClear( GL_COLOR_BUFFER_BIT ); //clear screen glBegin( GL_POINTS ); //draw points glVertex2i( 100, 50 ); //draw a point glVertex2i( 100, 150 ); //draw a point glVertex2i( 200, 200 ); //draw a point glEnd(); glBegin( GL_LINES ); //draw lines glVertex2i( 20, 20 ); //horizontal line glVertex2i( 400, 20 ); glVertex2i( 20, 10 ); //vertical line glVertex2i( 20, 400 ); glEnd(); glBegin( GL_LINE_STRIP ); //draw polyline glVertex2i( 200, 100 ); glVertex2i( 300, 100 ); glVertex2i( 450, 200 ); glVertex2i( 200, 100 ); glEnd(); glColor3f( 0.6, 0.6, 0.6 ); //bright grey glRecti( 400, 400, 450, 480 ); glColor3f( 1.0, 0.0, 0.0 ); //red glRecti( 350, 350, 380, 390 ); glFlush(); //send all output to screen } ------------------------------------------------------------------------------ //draw_main.cpp: main loop of drawing program #include <GL/glut.h> #include <math.h> #include <stdlib.h> #include <stdio.h> //initialization void init(void); //does the drawing void display(void); /* Main Loop * Open window with initial window size, title bar, * RGBA display mode, depth buffer. */ int main(int argc, char** argv) { glutInit(&argc, argv); //initialize toolkit glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB ); //set display mode: single bufferring, RGBA model glutInitWindowSize(500, 500); //set window size on screen glutInitWindowPosition( 100, 150 ); //set window position on screen glutCreateWindow(argv[0]); //open screen window init(); glutDisplayFunc (display); //points to display function glutMainLoop(); //go into perpetual loop return 0; }

     
     
   • Using mouse and keys
     

     //mouse_key.cpp #include <GL/glut.h> #include <stdlib.h> #define screenHeight 500 //initialization void init( void ) { glClearColor( 1.0, 1.0, 1.0, 0.0 ); //get white background color glColor3f( 0.0f, 0.0f, 0.0f ); //set drawing color glPointSize( 4.0 ); //a dot is 4x4 glMatrixMode( GL_PROJECTION ); glLoadIdentity(); gluOrtho2D( 0.0, 500.0, 0.0, 500.0 ); } //init void display() { glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT ); glFlush(); } void drawDot( int x, int y ) { glBegin( GL_POINTS ); glVertex2i( x, y ); //draw a points glEnd(); } //drawDot void myMouse( int button, int state, int x, int y ) { if ( button == GLUT_LEFT_BUTTON && state == GLUT_DOWN ) drawDot( x, screenHeight - y ); glFlush(); //send all output to screen } void myMovedMouse( int mouseX, int mouseY) { GLint x = mouseX; GLint y = screenHeight - mouseY; GLint brushsize = 6; glColor3f( 1.0, 0.0, 0.0 ); glRecti ( x, y, x + brushsize, y + brushsize ); glFlush(); } //myMovedMouse void myKeyboard ( unsigned char key, int mouseX, int mouseY ) { GLint x = mouseX; GLint y = screenHeight - mouseY; switch( key ) { case 'p': drawDot ( x, y ); break; case 'e': exit ( -1 ); default : break; } } //mouse_key_main.cpp: main loop of drawing program #include <GL/glut.h> #include <math.h> #include <stdlib.h> #include <stdio.h> //initialization void init(void); void myMouse( int button, int state, int x, int y); void myMovedMouse( int mouseX, int mouseY); void myKeyboard ( unsigned char key, int x, int y ); void display( void ); /* Main Loop * Open window with initial window size, title bar, * RGBA display mode, depth buffer. */ int main(int argc, char** argv) { glutInit(&argc, argv); //initialize toolkit glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB ); //set display mode glutInitWindowSize(500, 500); //set window size on screen glutInitWindowPosition( 100, 150 ); //set window position on screen glutCreateWindow(argv[0]); //open screen widow init(); glutMouseFunc( myMouse ); glutMotionFunc( myMovedMouse ); glutKeyboardFunc( myKeyboard ); glutDisplayFunc( display ); glutMainLoop(); //go into perpetual loop return 0; } ------------------------------------------------------------------ #sample Makefile for using OpenGL of Red Hat Linux 7.x #CS 420, Tong Yu, Fall 2002 PROG = mouse_key CFLAGS = -w -s -O2 -ansi -DSHM XLIBS = -lX11 -lXext -lXmu -lXext -lXmu -lXt -lXi -lSM -lICE LIBS = -lglut -lGLU -lGL INCLS = -I/usr/X11R/include -I/share/mesa/include LIBDIR = -L/usr/X11/lib -L/usr/X11R6/lib #source codes SRCS = mouse_key_main.cpp mouse_key.cpp #substitute .cpp by .o to obtain object filenames OBJS = $(SRCS:.cpp=.o) #$< evaluates to the target's dependencies, #$@ evaluates to the target $(PROG): $(OBJS) g++ -o $@ $(OBJS) $(LIBDIR) $(LIBS) $(XLIBS) $(OBJS): g++ -c $*.cpp $(INCLS) clean: rm $(OBJS) $(PROG)