/* simple4.c 

   draws an n-gon with n vertices

   Features:    
   - moving left/right/up/dpwn when the user presses l/r/u/d keys

   the movement is implemented by keeping track of the current
   translation. Whenever the user presses L or R, the current
   translation matrix is updated to reflect the new translation and
   the scene is displayed.  display() draws the polygon in the origin
   and applies the translation matrix.
   
   More features: 
   - number of vertices can be increased/decreased  with <,>
   - the radius can be increased/decreased with +, -
   
   OpenGL 1.x
   Laura Toma
 */



#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <assert.h>
//this allows this code to compile both on apple and linux platforms
#ifdef __APPLE__
#include <GLUT/glut.h>
#else
#include <GL/glut.h>
#endif


/* global variables */
const int WINDOWSIZE = 500; 

//we predefine some colors for convenience 
GLfloat red[3] = {1.0, 0.0, 0.0};
GLfloat green[3] = {0.0, 1.0, 0.0};
GLfloat blue[3] = {0.0, 0.0, 1.0};
GLfloat black[3] = {0.0, 0.0, 0.0};
GLfloat white[3] = {1.0, 1.0, 1.0};
GLfloat gray[3] = {0.5, 0.5, 0.5};
GLfloat yellow[3] = {1.0, 1.0, 0.0};
GLfloat magenta[3] = {1.0, 0.0, 1.0};
GLfloat cyan[3] = {0.0, 1.0, 1.0};


GLint fillmode = 0;

float r = .5;  //default radius
int n = 6;  //default nb of vertices

/* This is the global translation; it is updated when the user presses
   L/R/U/D */
GLfloat pos[3] = {0,0,0};


/* forward declarations of functions */
void display(void);
void keypress(unsigned char key, int x, int y);
void draw_ngon(); 




int main(int argc, char** argv) {

    /* open a window and initialize GLUT stuff */
  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
  glutInitWindowSize(WINDOWSIZE, WINDOWSIZE);
  glutInitWindowPosition(100,100);
  glutCreateWindow(argv[0]);

  /* register callback functions */
  glutDisplayFunc(display); 
  glutKeyboardFunc(keypress);
  
  /* OpenGL init */
  /* set background color black*/
  glClearColor(0, 0, 0, 0);  
  
  /* call the event handler */
  glutMainLoop();

  return 0;
}




/* this function is called whenever the window needs to be rendered */
void display(void) {

  //clear the screen
  glClear(GL_COLOR_BUFFER_BIT);
 //clear all transformations 
  glMatrixMode(GL_MODELVIEW); 
  glLoadIdentity();

  /* The default GL window is [-1,1]x[-1,1] with the origin in the
     center
  */ 
  
  /* First we translate our local reference system. pos[] represents
     the cumulative translation entered by the user */
  glTranslatef(pos[0], pos[1], pos[2]); 

  /* Now we draw the object in the local reference system. Note that
     we draw the polygon in the local system, and we translate the
     system. */
  draw_ngon();
  
  /* execute the drawing commands */
  glFlush();
}



/* this function is called whenever  key is pressed */
void keypress(unsigned char key, int x, int y) {
  switch(key) {
  case 'q':
    exit(0);
    break;

  case '+': 
    r *= 1.1; 
    glutPostRedisplay();
    break; 
 
  case '-': 
    r *= .9; 
    glutPostRedisplay();
    break; 
	
  case '<': 
    n--; 
    glutPostRedisplay();
    break; 
	
  case '>': 
    n++; 
    glutPostRedisplay();
    break; 

  case 'l': 
	pos[0]  -= 0.2; 
	glutPostRedisplay();
	break; 
  case 'r': 
	pos[0] += 0.2; 
	glutPostRedisplay();
	break;

  case 'u': 
    pos[1] += 0.2;
    glutPostRedisplay();
    break;

  case 'd': 
    pos[1] -= 0.2;
    glutPostRedisplay();
    break;

  case 'f': 
    fillmode = !fillmode; 
    glutPostRedisplay();
    break;
  } 
}

  
/* draw an n-gon with vertices in [-1,1]x[-1,1] centered at (0,0),
   with radius r and n sides. Note that r and n are global variables
   that are updated by the keypress() function */
void draw_ngon() {

  int i; 
  float a = 2*M_PI/n; 
 
  if (fillmode) {
    glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
  } else {
    glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
  }
  
 /* draw a polygon with n vertices centered at (0,0) */
  glBegin(GL_POLYGON);
  for (i=0; i<= n; i++) {
    glVertex2f(r*cos(a*i), r*sin(a*i));
  }
  glEnd();

}