/* sphere.c    */

/* E. Angel, Interactive Computer Graphics */
/* A Top-Down Approach with OpenGL, Third Edition */
/* Addison-Wesley Longman, 2003 */
/* Recursive subdivision of cube (Chapter 6). Three displaymodes: wire frame, constant, and interpolative shading *//*Program also illustrates defining materials and light sourcesin myiit() *//* mode 0 = wire frame, mode 1 = constant shading,mode 3 = interpolative shading */#include <stdlib.h>#include <GL/glut.h>typedef float point[4];/* initial tetrahedron */point v[]={{0.0, 0.0, 1.0}, {0.0, 0.942809, -0.33333},          {-0.816497, -0.471405, -0.333333}, {0.816497, -0.471405, -0.333333}};static GLfloat theta[] = {0.0,0.0,0.0};int n;int mode;void triangle( point a, point b, point c)/* display one triangle using a line loop for wire frame, a singlenormal for constant shading, or three normals for interpolative shading */{    if (mode==0) glBegin(GL_LINE_LOOP);    else glBegin(GL_POLYGON);       if(mode==1) glNormal3fv(a);       if(mode==2) glNormal3fv(a);       glVertex3fv(a);       if(mode==2) glNormal3fv(b);       glVertex3fv(b);       if(mode==2) glNormal3fv(c);       glVertex3fv(c);    glEnd();}void normal(point p){/* normalize a vector */    double sqrt();    float d =0.0;    int i;    for(i=0; i<3; i++) d+=p[i]*p[i];    d=sqrt(d);    if(d>0.0) for(i=0; i<3; i++) p[i]/=d;}void divide_triangle(point a, point b, point c, int m){/* triangle subdivision using vertex numbersrighthand rule applied to create outward pointing faces */    point v1, v2, v3;    int j;    if(m>0)    {        for(j=0; j<3; j++) v1[j]=a[j]+b[j];        normal(v1);        for(j=0; j<3; j++) v2[j]=a[j]+c[j];        normal(v2);        for(j=0; j<3; j++) v3[j]=b[j]+c[j];         normal(v3);        divide_triangle(a, v1, v2, m-1);        divide_triangle(c, v2, v3, m-1);        divide_triangle(b, v3, v1, m-1);        divide_triangle(v1, v3, v2, m-1);    }    else(triangle(a,b,c)); /* draw triangle at end of recursion */}void tetrahedron( int m){/* Apply triangle subdivision to faces of tetrahedron */    divide_triangle(v[0], v[1], v[2], m);    divide_triangle(v[3], v[2], v[1], m);    divide_triangle(v[0], v[3], v[1], m);    divide_triangle(v[0], v[2], v[3], m);}void display(void){/* Displays all three modes, side by side */    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);	   glLoadIdentity();    mode=0;    tetrahedron(n);    mode=1;    glTranslatef(-2.0, 0.0,0.0);    tetrahedron(n);    mode=2;    glTranslatef( 4.0, 0.0,0.0);    tetrahedron(n);    glFlush();}void myReshape(int w, int h){    glViewport(0, 0, w, h);    glMatrixMode(GL_PROJECTION);    glLoadIdentity();    if (w <= h)        glOrtho(-4.0, 4.0, -4.0 * (GLfloat) h / (GLfloat) w,            4.0 * (GLfloat) h / (GLfloat) w, -10.0, 10.0);    else        glOrtho(-4.0 * (GLfloat) w / (GLfloat) h,            4.0 * (GLfloat) w / (GLfloat) h, -4.0, 4.0, -10.0, 10.0);    glMatrixMode(GL_MODELVIEW);    display();}void myinit(){    GLfloat mat_specular[]={1.0, 1.0, 1.0, 1.0};    GLfloat mat_diffuse[]={1.0, 1.0, 1.0, 1.0};    GLfloat mat_ambient[]={1.0, 1.0, 1.0, 1.0};    GLfloat mat_shininess={100.0};    GLfloat light_ambient[]={0.0, 0.0, 0.0, 1.0};    GLfloat light_diffuse[]={1.0, 1.0, 1.0, 1.0};    GLfloat light_specular[]={1.0, 1.0, 1.0, 1.0};/* set up ambient, diffuse, and specular components for light 0 */    glLightfv(GL_LIGHT0, GL_AMBIENT, light_ambient);    glLightfv(GL_LIGHT0, GL_DIFFUSE, light_diffuse);    glLightfv(GL_LIGHT0, GL_SPECULAR, light_specular);/* define material proerties for front face of all polygons */    glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);    glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient);    glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);    glMaterialf(GL_FRONT, GL_SHININESS, mat_shininess);    glShadeModel(GL_SMOOTH); /*enable smooth shading */    glEnable(GL_LIGHTING); /* enable lighting */    glEnable(GL_LIGHT0);  /* enable light 0 */    glEnable(GL_DEPTH_TEST); /* enable z buffer */    glClearColor (1.0, 1.0, 1.0, 1.0);    glColor3f (0.0, 0.0, 0.0);}voidmain(int argc, char **argv){    n=5;    glutInit(&argc, argv);    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);    glutInitWindowSize(500, 500);    glutCreateWindow("sphere");    myinit();    glutReshapeFunc(myReshape);    glutDisplayFunc(display);    glutMainLoop();}