#include
#include "math.h"
#define M_PI 3.14159

/* drawColorSphere(r, segs) - Draw a colorful sphere centered on the local
origin, with radius r and approximated by segs polygon segments.
*/
void drawColorSphere(float r, int segs) {
int i, j;
float x, y, z, z1, z2, R, R1, R2;

// Top cap: a triangle fan
glBegin(GL_TRIANGLE_FAN);
glNormal3f(0,0,1);
glColor3f(0.5,0.5,1);
glVertex3f(0,0,r);
z = cos(M_PI/segs);
R = sin(M_PI/segs);
for(i = 0; i <= 2*segs; i++) {
x = R*cos(i*2.0*M_PI/(2*segs));
y = R*sin(i*2.0*M_PI/(2*segs));
glNormal3f(x, y, z);
glColor3f(0.5*(x+1), 0.5*(y+1), 0.5*(z+1));
glVertex3f(r*x, r*y, r*z);
}
glEnd();

// Height segments: each a triangle strip
for(j = 1; j < segs-1; j++) {
z1 = cos(j*M_PI/segs);
R1 = sin(j*M_PI/segs);
z2 = cos((j+1)*M_PI/segs);
R2 = sin((j+1)*M_PI/segs);
glBegin(GL_TRIANGLE_STRIP);
for(i = 0; i <= 2*segs; i++) {
x = R1*cos(i*2.0*M_PI/(2*segs));
y = R1*sin(i*2.0*M_PI/(2*segs));
glNormal3f(x, y, z1);
glColor3f(0.5*(x+1), 0.5*(y+1), 0.5*(z1+1));
glVertex3f(r*x, r*y, r*z1);
x = R2*cos(i*2.0*M_PI/(2*segs));
y = R2*sin(i*2.0*M_PI/(2*segs));
glNormal3f(x, y, z2);
glColor3f(0.5*(x+1), 0.5*(y+1), 0.5*(z2+1));
glVertex3f(r*x, r*y, r*z2);
}
glEnd();
}

// Bottom cap: a triangle fan
glBegin(GL_TRIANGLE_FAN);
glNormal3f(0,0,-1);
glColor3f(0.5,0.5,0);
glVertex3f(0,0,-r);
z = -cos(M_PI/segs);
R = sin(M_PI/segs);
for(i = 2*segs; i >= 0; i--) {
x = R*cos(i*2.0*M_PI/(2*segs));
y = R*sin(i*2.0*M_PI/(2*segs));
glNormal3f(x, y, z);
glColor3f(0.5*(x+1), 0.5*(y+1), 0.5*(z+1));
glVertex3f(r*x, r*y, r*z);
}
glEnd();
}

void display(void) {
glClear(GL_COLOR_BUFFER_BIT);
drawColorSphere(0.8,30);
glutSwapBuffers();
}

void init (void)
{
glClearColor (0.0, 0.0, 0.0, 0.0); /* select clearing olor */
glShadeModel(GL_FLAT);
}

int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB);

glutInitWindowSize (500, 500); //改为glutInitWindowSize (250, 250); 可以看出变换的仅仅是物体按比例大小的变换
glutInitWindowPosition (100, 100);
glutCreateWindow ("First");
init ();
glutDisplayFunc(display);
glutMainLoop();
return 0;
}