#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <GL/glut.h>

#define K 0.1

int n=300;
GLfloat alpha=0.f;
GLfloat rad=10;
GLfloat pos[] = {0, 0, 10, 1.f};
GLfloat dir[] = {0, 0, -1};
GLfloat cutOff=3.f;



void Idle(void)
{
  static int i;

  glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);

  glPushMatrix();
  glLoadIdentity();
//  glTranslatef(0,0,-10);
  //glutSolidTeapot(0.6); 
  i++;
  if (i>360) i=0;
  glRotatef(i,1,1,1);
  glutSolidSphere(0.8,n,n);
  glPopMatrix();
  glutSwapBuffers();
}


void Display(void)
{
}


void MyInit(void)
{
  GLfloat mat_specular[] = {1, 1, 1, 1.0};
  GLfloat mat_diffuse[] = {1, 1, 1, 1.0};
  GLfloat mat_shininess[] = {50.0};
  GLfloat specular[] = {0.5, 0.5, 0.5, 1};
  GLfloat diffuse[] = {0.5, 0.5, 0.5, 1};

  glClearColor(1,1,1,1);


/* Set up material */
  glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR, mat_specular);
  glMaterialfv(GL_FRONT_AND_BACK, GL_DIFFUSE, mat_diffuse);
  glMaterialfv(GL_FRONT_AND_BACK, GL_SHININESS, mat_shininess);

/* Set up light0 */
  glEnable(GL_LIGHTING);
  glEnable(GL_LIGHT0);
  glLightfv(GL_LIGHT0, GL_POSITION, pos);
  glLightfv(GL_LIGHT0, GL_DIFFUSE, diffuse);
  glLightfv(GL_LIGHT0, GL_SPECULAR, specular);
  glLightf(GL_LIGHT0,GL_SPOT_CUTOFF,cutOff);
  glLightfv(GL_LIGHT0,GL_SPOT_DIRECTION,dir);

  
  glDepthFunc(GL_LEQUAL);
  glEnable(GL_DEPTH_TEST);
  glShadeModel(GL_SMOOTH);
  printf("Usage:\n+,-: # of triangles\n");
  printf("a,z: size of the spot\n");
  printf("up,down: light position\n");
  printf("(the light always shines into the center)\n");
}


void myReshape(int w, int h)
{
  glViewport(0, 0, w, h);
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  glOrtho(-1,1,-1,1,-10,10);
  glMatrixMode(GL_MODELVIEW);
}

void Key(unsigned char key, int x, int y)
{

	switch (key){
		case '+': n++;break;
		case '-': n--;break;
		case 'a': cutOff+=K;break;
		case 'z': cutOff-=K;break;
		case 27: 
		case 'Q': 
		case 'q': exit(0);break;
	}
    glLightf(GL_LIGHT0,GL_SPOT_CUTOFF,cutOff);
	printf("n=%i\n",n);
}

void SpecKey(GLint key, int x, int y)
{

	switch (key){
		case GLUT_KEY_UP:   alpha+=K;break;
		case GLUT_KEY_DOWN: alpha-=K;break;
	}
	pos[0]=0;
	pos[1]=rad*sin(alpha);
	pos[2]=rad*cos(alpha);
    glLightfv(GL_LIGHT0, GL_POSITION, pos);
	dir[0]=-pos[0];
	dir[1]=-pos[1];
	dir[2]=-pos[2];
    glLightfv(GL_LIGHT0,GL_SPOT_DIRECTION,dir);
	printf("pos=%f %f %f\n",pos[0],pos[1],pos[2]);
}

int main(int argc, char **argv)
{
  glutInitWindowSize(400,400);
  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH);
  glutCreateWindow("fuBar");
  MyInit();
  glutDisplayFunc(Display);
  glutIdleFunc(Idle);
  glutKeyboardFunc(Key);
  glutSpecialFunc(SpecKey);
  glutReshapeFunc(myReshape);
  glutMainLoop();
  return 0;             /* ANSI C requires main to return int. */
}