#include <math.h>
#include <GL/gl.h>
#include <GL/glu.h>
#include <GL/glut.h>

#define PI 3.141592654
#define TWOPI 6.283185308

void Cartesian2spheric( double x, double y, double z, double radius, double *s, double *t)
{
   	*t = acos( z /radius ) / PI;

	if (y >= 0 )
	{
      		*s = acos( x / (radius * sin( PI * (*t) ) ) ) / TWOPI;
	}
  	else
	{
      		*s = ( PI + acos( x / ( radius * sin( PI * (*t) ) ) ) ) / TWOPI;
	}
}

void Spheric2cartesian( double rayon, double latitude, double longitude, double *x, double *y, double *z )
{
	*x = rayon * cos( latitude ) * cos( longitude );

	*y = rayon * cos( latitude ) * sin ( longitude );

	*z = rayon * sin( latitude ); 
	
} 

void DrawSphere( double r, int n )
{
  	int i, j;
   	double phi1, phi2, theta;
	double s, t;
   	double ex, ey, ez;
   	

   	if (r < 0)
      		r = -r;

   	if (n < 0)
      		n = -n;

   	if (n < 4 || r <= 0) 
	{
      		glBegin(GL_POINTS);
      		glVertex3f(0, 0, 0);
      		glEnd();
      		return;
   	}

   	for ( j = 0 ; j < n ; j++ ) 
	{
      		phi1 = j * TWOPI / n;
      		phi2 = (j + 1) * TWOPI / n;	//next phi

      		glBegin(GL_QUAD_STRIP);

      		for ( i = 0 ; i <= n  ; i++ ) 
		{
         		theta = i * PI / n;

        		ex = sin ( theta ) * cos ( phi2 );
			ey = sin ( theta ) * sin ( phi2 );
        		ez = cos ( theta );
        		glNormal3f(ex,ey,ez);

        		s = phi2 / TWOPI;       // column
			t = 1.0f - theta / PI;     // row
			glTexCoord2f(s, t);

        		glVertex3f( r * ex , r * ey , r * ez );

       
 			ex = sin ( theta ) * cos ( phi1 );
			ey = sin ( theta ) * sin ( phi1 );
        		ez = cos ( theta );
        		glNormal3f(ex,ey,ez);

        		s = phi1 / TWOPI;        // column
			t = 1.0f - theta / PI;      // row
        		glTexCoord2f(s, t);
 
			glVertex3f( r * ex , r * ey , r * ez );
      		}

      		glEnd();
	}		
}