#include <GL/glut.h>
#include <iostream>
#include <cstdio>
using namespace std;

typedef unsigned char uchar;

void disp(void);
void reshape(int x,int y);
void mouse(int button,int state, int x, int y);
void keyb(uchar key,int x,int y);

static int winx;
static int winy;
static double xbegin = -1.8;
static double xend=1.1;
static double ybegin = -1.2;
static double yend=1.2;


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

  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);
  glutCreateWindow("Fractal");
  glutInitWindowSize(600,600);
  // clear the background to white so we can see any holes
  glClearColor(1.0,1.0,1.0,0.0);
  glutDisplayFunc(disp);
  glutReshapeFunc(reshape);
  glutMouseFunc(mouse);
  glutKeyboardFunc(keyb);
  glutMainLoop();
}


void disp(void){
  glClear(GL_COLOR_BUFFER_BIT);

  // begin definition
  glBegin(GL_POINTS);

  // for each pixel on the screen
  for(float i=0;i<winx;i+=0.999){
    for(float j=0;j<winy;j+=0.999){

      // define z_0
      double zIm = j*(yend-ybegin)/(winy*1.0)+ybegin;
      double zRe = i*(xend-xbegin)/(winx*1.0)+xbegin;

      // define c
      // alter this sequence to create a Julia set
      // e.g
      //       double cIm = 0.5;
      //       double cRe = 0.5;

      double cIm = zIm;
      double cRe = zRe;

      // res is the iteration counter
      double temp;
      int res = 0;

      // we take 255 iteration at max, resulting in 255 distinct
      // blue's
      while(res<255 && (zIm*zIm + zRe*zRe)<=4.0 ){
	// z^2= (a+bj)*(a+bj)= a^2 - b^2 + j*(2*a*b)
	//	temp = zRe*zRe - zIm *zIm + i*(xend-xbegin)/(winx*1.0)+xbegin;
	//	zIm =  2*zRe * zIm + j*(yend-ybegin)/(winy*1.0)+ybegin;
	temp = zRe*zRe - zIm *zIm + cRe;
	zIm =  2*zRe * zIm + cIm;
	zRe = temp;
	res++;
      }

      // define the color which is the number of iterations
      // here we link the number of iteration to the blue byte
      glColor3f(0,0,(res*1.0)/255.0);
      glVertex2f(i,j);
    }
  }
  glEnd();

  glutSwapBuffers();
}

void keyb(uchar key, int x, int y){
  if(key=='Q'||key=='q'){
    exit(0);
  }else if(key=='r'){
    xbegin = -1.8;
    xend=1.1;
    ybegin = -1.2;
    yend=1.2;
    reshape(winx,winy);
  }

}

void mouse(int button,int state,int x,int y){

  if(state == GLUT_DOWN){
    // remind the Y axis is point down and the X axis is pointing to the right
    y = winy - y;
    double dx = (xend-xbegin);
    double dy = (yend-ybegin);
    if(dx != 0 && dy != 0){
      if(button == GLUT_LEFT){
	xend = x * dx/winx +xbegin  + dx/10;
	xbegin = x * dx/winx +xbegin  - dx/10;
	
	yend = y * dy/winy +ybegin  + dy/10;
	ybegin = y * dy/winy +ybegin  - dy/10;
      }else{
	xend = x * dx/winx +xbegin  + 5*dx;
	xbegin = x * dx/winx +xbegin  - 5*dx;
	
	yend = y * dy/winy +ybegin  + 5*dy;
	ybegin = y * dy/winy +ybegin  - 5*dy;
	
      }
      glutPostRedisplay();
    }else{
      cout << "Underflow detected, zooming aborted" << endl; 
      cout << "Press 'r' to reset" << endl;
    }
  }
}

void reshape(int x,int y){
  winx =x;
  winy =y;
  glViewport(0,0,x,y);
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  gluOrtho2D(0,x,0,y);
  glMatrixMode(GL_MODELVIEW);
  glutPostRedisplay();
}