#include<windows.h>
#include"glut.h"
#include<math.h>

#define PI 3.141592654f
#define R 50
#define RADIUS 500

GLfloat mx , my , mz;
bool mFlag;

void init()
{
 glClearColor( 0.0f , 0.0f , 0.0f , 0.0f );
 glPolygonMode( GL_FRONT , GL_LINE );
 glPolygonMode( GL_BACK , GL_LINE );
}

void Resize( int w , int h )
{
 if(0==w || 0==h)
  return;
 glViewport( 0 , 0 , w , h );

 glMatrixMode(GL_PROJECTION);
 glLoadIdentity();
 if( w > h )
  glOrtho( -100*w/h , 100*w/h , -100 , 100 , 100 , -100 );
 else
  glOrtho( -100 , 100 , -100*h/w , 100*h/w , 100 , -100 );
 glMatrixMode(GL_MODELVIEW);
 glLoadIdentity();
 glutPostRedisplay();
}

void Display()
{
 GLfloat z , r , angle;
 glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
 glEnable( GL_DEPTH_TEST );

 glMatrixMode(GL_MODELVIEW);
 for( angle = 0; angle <= 2*PI; angle += (PI/18) )
 {
  glBegin( GL_TRIANGLE_STRIP );
  for( z = -R; z <= R; z += 5 )
  {
   r = sqrt( R*R - z*z );
   glVertex3f( r*cos(angle) , r*sin(angle) , z );
   glVertex3f( r*cos(angle+(PI/18)) , r*sin(angle+(PI/18)) , z );
  }//for
  glEnd();
 }//for
 glutSwapBuffers();
}

void Motion( int x , int y )
{
 if( false == mFlag )
  return;
 x = x-400;
 y = y-300;
 GLfloat z = sqrt( (GLfloat)(RADIUS*RADIUS - x*x - y*y ));
 //GLfloat Rot = 100 * acos( (mx*x + my*y + mz*z) / ( sqrt(mx*mx + my*my + mz*z) * sqrt(x*x + y*y + z*z) ) );
 GLfloat Rot = sqrt( (GLfloat)((x-mx)*(x-mx) + (y-my)*(y-my)) ) / 3;
 GLfloat lastMatrix[ 16 ];
 
 glMatrixMode(GL_MODELVIEW);
 glGetFloatv(GL_MODELVIEW_MATRIX,lastMatrix);
 glLoadIdentity();
 glRotatef( Rot , (my*z-y*mz) , (mx*z-x*mz) , (mx*y-x*my) );
 ::glMultMatrixf(lastMatrix);

 mx = x;
 my = y;
 mz = z;
 glutPostRedisplay();
}

void Mouse( int button , int state , int x , int y )
{
 if( GLUT_LEFT_BUTTON == button )
 {
  if( GLUT_DOWN == state )
  {
   mx = x-400;
   my = y-300;
   mz = sqrt( RADIUS*RADIUS - mx*mx - my*my );
   mFlag = true;
  }//if
  else
  {
   mFlag = false;
  }//else
 }//if
}

int main( int argc , char** argv )
{
 glutInit( &argc , argv );
 glutInitDisplayMode( GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH );
 glutInitWindowSize( 800 , 600 );
 glutCreateWindow( "Tom" );

 init();

 glutDisplayFunc( Display );
 glutReshapeFunc( Resize );
 glutMotionFunc( Motion );
 glutMouseFunc( Mouse );

 glutShowWindow();
 glutMainLoop();

 return 0;
}