// 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
#define _USE_MATH_DEFINES
#include <math.h>

#include <sstream>
using namespace std;

class Renderer {

public:
  float t;
  int width, height;
  double nearPlane, farPlane;
  int depthBits; 

public:
  Renderer() : t(0.0), nearPlane(2.0), farPlane(20.0) {}

public:

  void resize(int w, int h) {
    glViewport(0, 0, w, h);
    width = w;
    height = h;
  }

  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 (30.0, (float)width/(float)height, nearPlane, farPlane);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    // camera orbits in the y=10 plane
    // and looks at origin
    double rad = M_PI / 180.0f * t;
    gluLookAt(10.0*cos(rad), 10.0 , 10.0*sin(rad), // eye
              0.0, 0.0, 0.0, // look at
              0.0, 1.0, 0.0); // up

    //draw cube at origin
    drawCube();
  }

  void init() {
    glEnable(GL_DEPTH_TEST);
    glGetIntegerv (GL_DEPTH_BITS, &depthBits);
  }
private:
  void drawCube() {
    glColor3f(1.0,0.0,0.0);
    glBegin(GL_POLYGON);
    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();
    glColor3f(0.0,1.0,0.0);
    glBegin(GL_POLYGON);
    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();
    glColor3f(0.0,0.0,1.0);
    glBegin(GL_POLYGON);
    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();
    glColor3f(1.0,1.0,0.0);
    glBegin(GL_POLYGON);
    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();
    glColor3f(1.0,1.0,1.0);
    glBegin(GL_POLYGON);
    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();
    glColor3f(0.0,1.0,1.0);
    glBegin(GL_POLYGON);
    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();
  }
};

//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 timer(int v) 
{
  float offset = 1.0f;
  renderer->t += offset;
  glutDisplay();
  glutTimerFunc(unsigned(20), timer, ++v);
}

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

  switch(key) {
    case '1':
      renderer->nearPlane = 2.0;
      renderer->farPlane = 20.0;
      redraw = true;
      break;
    case '+':
      renderer->nearPlane *= 0.1;
      renderer->farPlane  *= 10.0;
      redraw = true;
      break;
    case '-':
      renderer->nearPlane *= 10.0;
      renderer->farPlane *= 0.1;
      if(renderer->nearPlane > 2.0) renderer->nearPlane = 2.0;
      if(renderer->farPlane < 20.0) renderer->farPlane = 20.0;
      redraw = true;
      break;
  }
  if(redraw) {
    std::stringstream ss;
    ss << "Precision: " << renderer->depthBits << "bits Near: " <<  renderer->nearPlane <<" Far: " << renderer->farPlane;
    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("ZFighting: Press + and - key to change near and far plane");

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

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

  glutTimerFunc(unsigned(20), timer, 0);

  glutMainLoop();
}