// This code example is created for educational purpose
// by Thorsten Thormaehlen (contact: www.thormae.de).
// It is distributed without any warranty.

#include <GL/freeglut.h> // we use glut here as window manager

#include <math.h>
#ifndef M_PI 
#define M_PI 3.1415926535897932385f 
#endif

#include <sstream>
#include <vector>
using namespace std;

class Renderer {

public:
  float t; //time
  const float d0; // initial distance

public:
  Renderer() : t(1.0), d0(3.0), width(0), height(0) {}

public:
  void display() {
    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective (dollyZoomFovy(), (float)width/(float)height, 0.1, 50.0);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    // translate camera by 3 units
    glTranslatef(0.0f, 0.0f, -t*d0);

    // draw a cube in the local coordinate system
    drawCube();
    // draw random lines
    drawRandomLines();
  }

  void init() {
    glEnable(GL_DEPTH_TEST);
    // create random values between -1.0 and 1.0
    for(unsigned r=0; r < 1000; r++) {
      int rval = rand();
      randVals.push_back(2.0f*float(rval)/float(RAND_MAX)-1.0f);
    }
  }

  void resize(int w, int h) {
    // ignore this for now
    glViewport(0, 0, w, h); 
    width = w;
    height = h;
  }

  float dollyZoomFovy() {
    float fovyInit = 60.0f; // initial field of view
    float theta = fovyInit / 180.0f * M_PI; // degree to rad
    float f = 1.0f / tan(theta/2.0f);
    float fNew = f * (d0*t-1) / (d0-1);
    float thetaNew = atan(1.0f / fNew) * 2.0f;
    float val = 180.0f * thetaNew / M_PI; //rad to degree
    return val;
  }

private:
  int width;
  int height;
  std::vector<float> randVals;

private:
  void drawCube() {

    glColor3f(1.0f, 1.0f, 1.0f);
    glLineWidth(3.0f);
    glBegin(GL_LINE_LOOP);
    glVertex3f(-1.0f, 1.0f, 1.0f);
    glVertex3f( 1.0f, 1.0f, 1.0f);
    glVertex3f( 1.0f,-1.0f, 1.0f);
    glVertex3f(-1.0f,-1.0f, 1.0f);
    glEnd();
    glBegin(GL_LINE_LOOP);
    glVertex3f(-1.0f, 1.0f,-1.0f);
    glVertex3f( 1.0f, 1.0f,-1.0f);
    glVertex3f( 1.0f,-1.0f,-1.0f);
    glVertex3f(-1.0f,-1.0f,-1.0f);
    glEnd();

    glBegin(GL_LINE_LOOP);
    glVertex3f( 1.0f, 1.0f,-1.0f);
    glVertex3f( 1.0f, 1.0f, 1.0f);
    glVertex3f( 1.0f,-1.0f, 1.0f);
    glVertex3f( 1.0f,-1.0f,-1.0f);
    glEnd();

    glBegin(GL_LINE_LOOP);
    glVertex3f(-1.0f, 1.0f,-1.0f);
    glVertex3f(-1.0f, 1.0f, 1.0f);
    glVertex3f(-1.0f,-1.0f, 1.0f);
    glVertex3f(-1.0f,-1.0f,-1.0f);
    glEnd();
    glLineWidth(1.0);
  }

  void drawRandomLines() {
    if(randVals.size() % 5) return;
    unsigned i = 0;
    while(i < randVals.size()) {
      glColor3f(fabs(randVals[i++]), fabs(randVals[i++]), fabs(randVals[i++]));
      float x = randVals[i++];
      float y = randVals[i++];
      glBegin(GL_LINES);
      glVertex3f(x, y, -1.0f);
      glVertex3f(x, y,  1.0f);
      glEnd();
    }
  }
};

//this is a static pointer to a Renderer used in the glut callback functions
static Renderer *renderer;

//glut static callbacks start
static void glutResize(int w, int h) 
{
  renderer->resize(w,h);
}

static void glutDisplay() 
{
  renderer->display();
  glutSwapBuffers();
}

static void glutKeyboard(unsigned char key, int x, int y) {
  bool redraw = false;
  float offset = 0.02f;

  if (glutGetModifiers() & GLUT_ACTIVE_ALT) {
    offset = -offset;
  }
  switch(key) {
    case '1':
      renderer->t += offset;
      if(renderer->t <  1.0f) renderer->t = 4.0f;
      if(renderer->t >  4.0f) renderer->t = 1.0f;
      redraw = true;
      break;
    case '0':
      renderer->t = 1.0f;
      redraw = true;
      break;
  }
  if(redraw) {
    float distance = renderer->t*renderer->d0;
    float fovy = renderer->dollyZoomFovy();

    std::stringstream ss;
    ss << "Distance: " <<  int(distance*10.0f)/10.0f <<" FieldofView: " << int(fovy*10.0f)/10.0f;
    glutSetWindowTitle(ss.str().c_str());
    glutDisplay();
  }
}


int main(int argc, char **argv) 
{
  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
  glutInitWindowPosition(100,100);
  glutInitWindowSize(320, 320);

  glutCreateWindow("Use the 1 key to perform a dolly zoom");

  glutDisplayFunc(glutDisplay);
  //glutIdleFunc(glutDisplay);
  glutReshapeFunc(glutResize);
  glutKeyboardFunc(glutKeyboard);

  renderer = new Renderer;
  renderer->init();

  glutMainLoop();
}