// Draws a sphere with radius "r" and n controls tesselation level
void CreateSphere(double r,int n)
{
   int i,j;
   double theta1,theta2,theta3;
   double e[3],p[3];

   if (r < 0) return;
   if (n < 4) return;

   for (j=0;j<n/2;j++) {
      theta1 = j * 2 * M_PI / n - M_PI/2;
      theta2 = (j + 1) * 2 * M_PI / n - M_PI/2;

      glBegin(GL_TRIANGLE_STRIP);
      for (i=0;i<=n;i++) {
         theta3 = i * 2 * M_PI / n;

         e[0] = -cos(theta2) * cos(theta3);
         e[1] = -sin(theta2);
         e[2] = -cos(theta2) * sin(theta3);
         p[0] = r * e[0];
         p[1] = r * e[1];
         p[2] = r * e[2];

         glVertexAttrib4dARB(2,e[0],e[1],e[2],2*r);
         glColor4d(0.5*e[0]+0.5,0.5*e[1]+0.5,0.5*e[2]+0.5, r/sqrt(3.0));
         glVertex3d(p[0],p[1],p[2]);

         e[0] = -cos(theta1) * cos(theta3);
         e[1] = -sin(theta1);
         e[2] = -cos(theta1) * sin(theta3);
         p[0] = r * e[0];
         p[1] = r * e[1];
         p[2] = r * e[2];

         glVertexAttrib4dARB(2,e[0],e[1],e[2],2*r);
         glColor4d(0.5*e[0]+0.5,0.5*e[1]+0.5,0.5*e[2]+0.5, r/sqrt(3.0));
         glVertex3d(p[0],p[1],p[2]);
      }
      glEnd();
   }

}


// Creates a display list and returns the list ID
//    This should be done once, probably in an initialization function.
GLuint CreateSphereDisplayList( void )
{
   GLuint sphereListID = glGenLists(1);
   glNewList( sphereListID, GL_COMPILE );
   CreateSphere( 1.0, 10 );  
   glEndList( );
   return sphereListID;
}

void display( void )
{

   // ... standard setup stuff, like clear screen...

   // Setup the location of the sphere
   // Setup the color of the sphere.

   if (usingDisplayList)
       glCallList( sphereListID );
   else
       CreateSphere( 1.0, 10 );

   // ... do standard per-frame cleanup ...
  
}