INT32GP Graphics Programming: Tutorial #01
Using OpenGL and GLUT

gcc -o $1 $1.c\
	-I/usr/local/pub/glut-3.6/include -lglut -lGLU -lGL -lXmu -lXi -lXext -lX11 -lm

• Decide where you want to keep the command. I have a subdirectory called bin for this purpose.
• Use a text editor (such as nedit) to create the file in the appropriate subdirectory. Very Important: the indent on the second line is one tab stop.
• Decide what name you want for your command. It cannot have the same name as other Unix commands (I use gccglut).
• Save the file using the name you have chosen.
• Change your permission for this file. You need executable permission for a script file.
• Assuming you have named your file gccglut, type the following on the Unix command line.

chmod u+x gccglut

• Create an alias so that you can access your new command (gccglut) from anywhere in your directory structure.
• Edit your .cshrc file by adding the following line or something similar.

alias gccglut "~/bin/gccglut"

• To activate the alias without having to log out and in again, use the following command.

source .cshrc

/*
** File:          square2.c
** Description:   A simple C program using OpenGL
**                and GLUT to render a yellow square
**                with a blue border on a white background.
** Rev:           1.0
** Created:       26 August 2001
** Last Update:   22 July 2002
** Author:        Fran Soddell
** Email:         F.Soddell@bendigo.latrobe.edu.au
*/
#include <GL/glut.h>
/*
** colour management
*/
#define NUM_COLOURS 8
#define ALPHA 0.0
enum {black,
      red,green,blue,
      yellow,magenta,cyan,
      white
};
typedef GLfloat colourType[3];
colourType colour[NUM_COLOURS]={
   {0.0,0.0,0.0},
   {1.0,0.0,0.0},{0.0,1.0,0.0},{0.0,0.0,1.0},
   {1.0,1.0,0.0},{1.0,0.0,1.0},{0.0,1.0,1.0},
   {1.0,1.0,1.0}
};
/*
** model management
*/
enum {x,y};
typedef GLdouble vertexType [2];
int numVertices=4;
vertexType square[]={
   {0.5,0.5},{-0.5,0.5},{-0.5,-0.5},{0.5,-0.5}
};
/*
**  ***********************************************************
*/
void render(vertexType * image, int numVertices, int primitive){
   int i;
   glBegin(primitive);
      for(i=0;i<numVertices;i++)
         glVertex2d(image[i][x],image[i][y]);
   glEnd();
}
void renderView(){
   glColor3fv(colour[yellow]);
   render(square,numVertices,GL_POLYGON);
   glColor3fv(colour[blue]);
   render(square,numVertices,GL_LINE_LOOP);
}
void display(){
   /*
   ** Clear the window with the background colour before
   ** (re)rendering.
   */
   glClear(GL_COLOR_BUFFER_BIT);
   renderView();
   glFlush();
}
void setUpGLUT(int argc,char ** argv){
   glutInit(&argc,argv);
   glutCreateWindow("Square");
   /*
   ** Register callbacks.
   */
   glutDisplayFunc(display);
}
void initialiseGL(){
   /*
   ** Set the background colour
   ** (clear colour) to white.
   */
   glClearColor(1,1,1,ALPHA);
}
int main(int argc,char ** argv){
   setUpGLUT(argc,argv);
   initialiseGL();
   /*
   ** Display window and enter the GLUT event
   ** processing loop.
   */
   glutMainLoop();
   return 0;
}

gccglut square

You may get a compiler warning that a library file is not used. Not all libraries are needed for every compilation so you may ignore this warning.

• Include the header file, stdio.h, that tells the compiler where to find the functions that print ASCII to the command line. Include it at the top of your program (under the include for glut.h). Some compilers will not complain if you forget this but others will and we want to write portable code.

#include <GL/glut.h>
#include <stdio.h>

• Register your keyboard function (to be called keyboard) in the setUpGlut()function.

glutKeyboardFunc(keyboard);

• Write your function. Position it above setUpGlut. Some C compilers may not complain if you put functions in the wrong order but others will (write portable code). Note that GLUT passes an unsigned char (key pressed) and two ints (x and y position of the mouse on the screen) to the function.

void keyboard(unsigned char key,int xMouse,int yMouse){
   switch(key){
      case 27:
         exit(0);
      default:
         printf("%s%c\n","key=",key);
   }
}

• Compile and run the program again. Does it perform as expected?
• What happens to the yellow square when you resize the GLUT window?
• Here is the 1996 version of the GLUT API specification. It is a pdf file (Acrobat reader).
1. Consult the GLUT API for more details about the function used in this tutorial.
2. Investigate other functions that you are interested in using.

• Install and configure an OpenGL development environment for both Windows (using MinGW32, a GCC port) and Linux. Information supplied by Grant Byers. Thank you Grant!
• Download free Borland C++ compiler for Windows.
• Supplementary information about installing the compiler. The information about how to configure your system is more useful than that in the readme file that comes with the compiler.
• Web address of plug in for the free Borland C++ compiler to give it a GUI shell. Information supplied by Bruce Eckart. Thank you Bruce!