```/* \$Id: gears.c,v 3.0 1998/02/14 18:42:29 brianp Exp \$ */

/*
* 3-D gear wheels.  This program is in the public domain.
*
* Brian Paul
*/

/* Conversion to GLUT by Mark J. Kilgard */

/*
* \$Log: gears.c,v \$
* Revision 3.0  1998/02/14 18:42:29  brianp
* initial rev
*
*/

#include <math.h>
#include <stdlib.h>
#include <GL/glut.h>

#ifndef M_PI
#define M_PI 3.14159265
#endif

/**

Draw a gear wheel.  You'll probably want to call this function when
building a display list since we do a lot of trig here.

width - width of gear
teeth - number of teeth
tooth_depth - depth of tooth

**/

static void
GLint teeth, GLfloat tooth_depth)
{
GLint i;
GLfloat r0, r1, r2;
GLfloat angle, da;
GLfloat u, v, len;

r1 = outer_radius - tooth_depth / 2.0;
r2 = outer_radius + tooth_depth / 2.0;

da = 2.0 * M_PI / teeth / 4.0;

glNormal3f(0.0, 0.0, 1.0);

/* draw front face */
for (i = 0; i <= teeth; i++) {
angle = i * 2.0 * M_PI / teeth;
glVertex3f(r0 * cos(angle), r0 * sin(angle), width * 0.5);
glVertex3f(r1 * cos(angle), r1 * sin(angle), width * 0.5);
glVertex3f(r0 * cos(angle), r0 * sin(angle), width * 0.5);
glVertex3f(r1 * cos(angle + 3 * da), r1 * sin(angle + 3 * da), width * 0.5);
}
glEnd();

/* draw front sides of teeth */
da = 2.0 * M_PI / teeth / 4.0;
for (i = 0; i < teeth; i++) {
angle = i * 2.0 * M_PI / teeth;

glVertex3f(r1 * cos(angle), r1 * sin(angle), width * 0.5);
glVertex3f(r2 * cos(angle + da), r2 * sin(angle + da), width * 0.5);
glVertex3f(r2 * cos(angle + 2 * da), r2 * sin(angle + 2 * da), width * 0.5);
glVertex3f(r1 * cos(angle + 3 * da), r1 * sin(angle + 3 * da), width * 0.5);
}
glEnd();

glNormal3f(0.0, 0.0, -1.0);

/* draw back face */
for (i = 0; i <= teeth; i++) {
angle = i * 2.0 * M_PI / teeth;
glVertex3f(r1 * cos(angle), r1 * sin(angle), -width * 0.5);
glVertex3f(r0 * cos(angle), r0 * sin(angle), -width * 0.5);
glVertex3f(r1 * cos(angle + 3 * da), r1 * sin(angle + 3 * da), -width * 0.5);
glVertex3f(r0 * cos(angle), r0 * sin(angle), -width * 0.5);
}
glEnd();

/* draw back sides of teeth */
da = 2.0 * M_PI / teeth / 4.0;
for (i = 0; i < teeth; i++) {
angle = i * 2.0 * M_PI / teeth;

glVertex3f(r1 * cos(angle + 3 * da), r1 * sin(angle + 3 * da), -width * 0.5);
glVertex3f(r2 * cos(angle + 2 * da), r2 * sin(angle + 2 * da), -width * 0.5);
glVertex3f(r2 * cos(angle + da), r2 * sin(angle + da), -width * 0.5);
glVertex3f(r1 * cos(angle), r1 * sin(angle), -width * 0.5);
}
glEnd();

/* draw outward faces of teeth */
for (i = 0; i < teeth; i++) {
angle = i * 2.0 * M_PI / teeth;

glVertex3f(r1 * cos(angle), r1 * sin(angle), width * 0.5);
glVertex3f(r1 * cos(angle), r1 * sin(angle), -width * 0.5);
u = r2 * cos(angle + da) - r1 * cos(angle);
v = r2 * sin(angle + da) - r1 * sin(angle);
len = sqrt(u * u + v * v);
u /= len;
v /= len;
glNormal3f(v, -u, 0.0);
glVertex3f(r2 * cos(angle + da), r2 * sin(angle + da), width * 0.5);
glVertex3f(r2 * cos(angle + da), r2 * sin(angle + da), -width * 0.5);
glNormal3f(cos(angle), sin(angle), 0.0);
glVertex3f(r2 * cos(angle + 2 * da), r2 * sin(angle + 2 * da), width * 0.5);
glVertex3f(r2 * cos(angle + 2 * da), r2 * sin(angle + 2 * da), -width * 0.5);
u = r1 * cos(angle + 3 * da) - r2 * cos(angle + 2 * da);
v = r1 * sin(angle + 3 * da) - r2 * sin(angle + 2 * da);
glNormal3f(v, -u, 0.0);
glVertex3f(r1 * cos(angle + 3 * da), r1 * sin(angle + 3 * da), width * 0.5);
glVertex3f(r1 * cos(angle + 3 * da), r1 * sin(angle + 3 * da), -width * 0.5);
glNormal3f(cos(angle), sin(angle), 0.0);
}

glVertex3f(r1 * cos(0), r1 * sin(0), width * 0.5);
glVertex3f(r1 * cos(0), r1 * sin(0), -width * 0.5);

glEnd();

/* draw inside radius cylinder */
for (i = 0; i <= teeth; i++) {
angle = i * 2.0 * M_PI / teeth;
glNormal3f(-cos(angle), -sin(angle), 0.0);
glVertex3f(r0 * cos(angle), r0 * sin(angle), -width * 0.5);
glVertex3f(r0 * cos(angle), r0 * sin(angle), width * 0.5);
}
glEnd();

}

static GLfloat view_rotx = 20.0, view_roty = 30.0, view_rotz = 0.0;
static GLint gear1, gear2, gear3;
static GLfloat angle = 0.0;

static GLuint limit;
static GLuint count = 1;

static void
draw(void)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glPushMatrix();
glRotatef(view_rotx, 1.0, 0.0, 0.0);
glRotatef(view_roty, 0.0, 1.0, 0.0);
glRotatef(view_rotz, 0.0, 0.0, 1.0);

glPushMatrix();
glTranslatef(-3.0, -2.0, 0.0);
glRotatef(angle, 0.0, 0.0, 1.0);
glCallList(gear1);
glPopMatrix();

glPushMatrix();
glTranslatef(3.1, -2.0, 0.0);
glRotatef(-2.0 * angle - 9.0, 0.0, 0.0, 1.0);
glCallList(gear2);
glPopMatrix();

glPushMatrix();
glTranslatef(-3.1, 4.2, 0.0);
glRotatef(-2.0 * angle - 25.0, 0.0, 0.0, 1.0);
glCallList(gear3);
glPopMatrix();

glPopMatrix();

glutSwapBuffers();

count++;
if (count == limit) {
exit(0);
}
}

static void
idle(void)
{
angle += 2.0;
glutPostRedisplay();
}

/* change view angle, exit upon ESC */
/* ARGSUSED1 */
static void
key(unsigned char k, int x, int y)
{
switch (k) {
case 'z':
view_rotz += 5.0;
break;
case 'Z':
view_rotz -= 5.0;
break;
case 27:  /* Escape */
exit(0);
break;
default:
return;
}
glutPostRedisplay();
}

/* change view angle */
/* ARGSUSED1 */
static void
special(int k, int x, int y)
{
switch (k) {
case GLUT_KEY_UP:
view_rotx += 5.0;
break;
case GLUT_KEY_DOWN:
view_rotx -= 5.0;
break;
case GLUT_KEY_LEFT:
view_roty += 5.0;
break;
case GLUT_KEY_RIGHT:
view_roty -= 5.0;
break;
default:
return;
}
glutPostRedisplay();
}

/* new window size or exposure */
static void
reshape(int width, int height)
{
GLfloat h = (GLfloat) height / (GLfloat) width;

glViewport(0, 0, (GLint) width, (GLint) height);
glMatrixMode(GL_PROJECTION);
glFrustum(-1.0, 1.0, -h, h, 5.0, 60.0);
glMatrixMode(GL_MODELVIEW);
glTranslatef(0.0, 0.0, -40.0);
}

static void
init(void)
{
static GLfloat pos[4] =
{5.0, 5.0, 10.0, 0.0};
static GLfloat red[4] =
{0.8, 0.1, 0.0, 1.0};
static GLfloat green[4] =
{0.0, 0.8, 0.2, 1.0};
static GLfloat blue[4] =
{0.2, 0.2, 1.0, 1.0};

glLightfv(GL_LIGHT0, GL_POSITION, pos);
glEnable(GL_CULL_FACE);
glEnable(GL_LIGHTING);
glEnable(GL_LIGHT0);
glEnable(GL_DEPTH_TEST);

/* make the gears */
gear1 = glGenLists(1);
glNewList(gear1, GL_COMPILE);
glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, red);
gear(1.0, 4.0, 1.0, 20, 0.7);
glEndList();

gear2 = glGenLists(1);
glNewList(gear2, GL_COMPILE);
glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, green);
gear(0.5, 2.0, 2.0, 10, 0.7);
glEndList();

gear3 = glGenLists(1);
glNewList(gear3, GL_COMPILE);
glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, blue);
gear(1.3, 2.0, 0.5, 10, 0.7);
glEndList();

glEnable(GL_NORMALIZE);
}

void
visible(int vis)
{
if (vis == GLUT_VISIBLE)
glutIdleFunc(idle);
else
glutIdleFunc(NULL);
}

int main(int argc, char *argv[])
{
glutInit(&argc, argv);
if (argc > 1) {
/* do 'n' frames then exit */
limit = atoi(argv[1]) + 1;
} else {
limit = 0;
}
glutInitDisplayMode(GLUT_RGB | GLUT_DEPTH | GLUT_DOUBLE);

glutInitWindowPosition(0, 0);
glutInitWindowSize(300, 300);
glutCreateWindow("Gears");
init();

glutDisplayFunc(draw);
glutReshapeFunc(reshape);
glutKeyboardFunc(key);
glutSpecialFunc(special);
glutVisibilityFunc(visible);

glutMainLoop();
return 0;             /* ANSI C requires main to return int. */
}
```