Alexander Graham Bell is alive and well in NewYork
and still awaiting a dial tone.

Concept 7.3 : Independently Moving the Light
============================================

On your left you should see a simple torus drawn
in red.  At the center of the torus you should 
also see a white cube depicting the position of 
the light source.
The left mouse button starts the animation. You should 
see the light move.
Also notice the specular hightlight shift from the top of 
the torus to the bottom, then become invisible (when 
the light moves to the back of the torus) and then be 
visible again.  Also notice how the ambient lighting changes 
from the front to the back and then the front again and so
on.

Our display routine in this case looks like :

void display(void)
{
   glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
   glEnable(GL_DEPTH_TEST); 
   glPushMatrix();
   glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, 
	        mat_amb_diff_white);
   glMaterialfv(GL_FRONT, GL_EMISSION, mat_no_emissivity);
   glLoadIdentity();
   gluLookAt(0.0, 0.0, 10.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
   glPushMatrix();
   
   glRotated(spin, 1.0, 0.0, 0.0);
   glLightfv(GL_LIGHT0, GL_POSITION, light_position);
   glTranslatef(0.0, 0.0, 1.5);
   
   glutWireSphere(0.10, 30, 30);
   glPopMatrix();
   glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);
   glMaterialfv(GL_FRONT, GL_SHININESS, mat_shininess);
   glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE,
	         mat_amb_diff_red);
   glutSolidTorus(0.275, 0.85, 8, 15);
   
   glPopMatrix();
   glFlush ();
}