One OpenGL example

1. Initialization procedures
2. Callback Functions
3. main()
4. Window and coordinate system creation
5. State initialization
6. Callback functions registration
7. Infinite Event Handling loop

code:

#include
#include
#include
static GLfloat spin = 0.0; // degree of spinning
void myInit(void)
{
glClearColor (1.0, 1.0, 1.0, 0.0); // set black background color
glShadeModel (GL_FLAT);
}
void myDisplay(void)
{ int xc = 0;
int yc = 0;
int rad = 20;
glClear(GL_COLOR_BUFFER_BIT); // clear the screen
// glPushMatrix ();
glRotatef (spin, 0.0, 1.0, 0.0);
glColor3f (1.0, 0.0, 0.0); // set the drawing color
glBegin(GL_LINE_LOOP);
for (int angle=0; angle< 365; angle=angle+5)
{
float angle_radians = angle * (float)3.14159 / (float)180;
float x = xc + rad * (float)cos(angle_radians);
float y = yc + rad * (float)sin(angle_radians);
glVertex2f(x,y);
}
glEnd();
spin += 5.0f; //
glPopMatrix ();
glutSwapBuffers ();
}

void myReshape ( int w, int h)
{
glViewport (0, 0, (GLsizei) w, (GLsizei) h);
glMatrixMode (GL_PROJECTION); // set "camera shape"
glLoadIdentity (); // clear the matrix
// viewing transformation
glOrtho (-40.0, 40.0, -40.0, 40.0, -1.0, 1.0);
glMatrixMode (GL_MODELVIEW);
glLoadIdentity ();
}

void myMouse(int button, int state, int x, int y)
{
switch (button) {
case GLUT_LEFT_BUTTON:
if (state == GLUT_DOWN)
glutIdleFunc(myDisplay);
break;
case GLUT_MIDDLE_BUTTON:
if (state == GLUT_DOWN)
glutIdleFunc(NULL);
break;
case GLUT_RIGHT_BUTTON:
if (state == GLUT_DOWN)
exit (-1);
break;
}
}

/*
*Request double buffer display mode.
* Register mouse input callback functions
*/

int main(int argc, char** argv)
{
glutInit(&argc, argv); // initialize the toolkit
glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB); // set display mode
glutInitWindowSize (250, 250); // set screen window size
glutInitWindowPosition (100, 100); // set window position on screen
glutCreateWindow (argv[0]); // open the screen window
myInit ();
glutDisplayFunc(myDisplay); // register redraw function
glutReshapeFunc(myReshape); // register reshape function
glutMouseFunc(myMouse); // register myMouse function
//glutIdleFunc(&myDisplay);
glutMainLoop(); // go into a perpetual loop
return 0;
}