/* simple4.c 

   draw an n-gon with n vertices,  moving left/right when press l/r keys

   the movement is implemented by keeping track of the center fof the
   polygon as a global variable, and moving it L/R

   note: another option would be to always draw the polygon centered
   at the origin, and use translation to move it L/R

   number of vertices can be increased/decreased, also the radius
   OpenGL 1.x
   Laura Toma
 */



#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <assert.h>

#ifdef __APPLE__
#include <GLUT/glut.h>
#else
#include <GL/glut.h>
#endif


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


/* we keep track globally of the coordinates of the center of the
   rectangle; they will be updated by the keys that implement move
   left and right */
GLfloat x_center = 0.0, y_center = 0.0;


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


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

    /* open a window */
  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
  glutInitWindowSize(500, 500);
  glutInitWindowPosition(100,100);
  glutCreateWindow(argv[0]);

  /* OpenGL init */
  glClearColor(0, 0, 0, 0);   /* set background color black*/
  glEnable(GL_DEPTH_TEST); //not necessary in 2D
    
  /* callback functions */
  glutDisplayFunc(display); 
  glutKeyboardFunc(keypress);

  
  /* event handler */
  glutMainLoop();
  return 0;
}



//draw an n-gon centered at (x_center, y_center)
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 centered at x_center, y_center */
  glBegin(GL_POLYGON);
  for (i=0; i<= n; i++) {
    glVertex2f(x_center + r*cos(a*i), y_center + r*sin(a*i));
  }
  glEnd();

}




void display(void) {

  glClear(GL_COLOR_BUFFER_BIT);
  draw_ngon();
  glFlush();
}


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': 
	x_center -= 0.2; 
	glutPostRedisplay();
	break; 
  case 'r': 
	x_center += 0.2; 
	glutPostRedisplay();
	break;

  case 'u': 
    y_center += 0.2;
    glutPostRedisplay();
    break;

  case 'd': 
    y_center -= 0.2;
    glutPostRedisplay();
    break;

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