/*
  Jernej Barbic
  University of Southern California
  January 2012
 
  A basic OpenGL program with GLUT. 
*/


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

// standard OpenGL include files
// the location of these files varies by platform
#if defined(WIN32) || defined(linux)
  #include <GL/gl.h>
  #include <GL/glu.h>
  #include <GL/glut.h>
#elif defined(__APPLE__)
  #include <OpenGL/gl.h>
  #include <OpenGL/glu.h>
  #include <GLUT/glut.h>
#endif

int windowID;
int windowWidth, windowHeight;
double angle = 0.0;
double cameraHeight = 1.0;

void Init()
{
  // set the screen background color to RGB (200, 200, 45) (light yellow)
  glClearColor(200.0 / 255, 200.0 / 255, 45.0 / 255, 0.0);

  // enable the depth test (important; disabled by default)
  glEnable(GL_DEPTH_TEST);

  //glShadeModel(GL_FLAT); // shade the entire triangle with a flat color
  glShadeModel(GL_SMOOTH); // interpolate vertex colors into the triangle interior
}

// this function gets called continuously (alternates execution with "Display")
void DoIdle() 
{
  angle += 0.001; // one of the two triangles circles
  //cameraHeight = 1.0;
  cameraHeight = 1.0 + 0.5 * sin(2*angle); // camera moves up and down
  glutPostRedisplay();
}

// this function gets called whenever the user resizes the window
// x = window x-size (in pixels)
// y = window y-size (in pixels)
void Reshape(int x, int y)
{
  windowWidth = x;
  windowHeight = y;

  glViewport(0,0,x,y);

  glMatrixMode(GL_PROJECTION); // select the projection matrix 
  glLoadIdentity(); // reset the projection matrix to identity

  // Calculate The Aspect Ratio Of The Window
  double minZPlane = 0.01;
  double maxZPlane = 10.0;
  double aspectRatio = 1.0 * windowWidth / windowHeight;
  gluPerspective(45.0f, aspectRatio, minZPlane, maxZPlane);

  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
}

// this function gets called whenever a key is pressed
void KeyboardFunc (unsigned char key, int x, int y)
{
  switch (key)
  {
    case 27:
      // ESC pressed, exit the application
      glutDestroyWindow(windowID);
      exit(0);
    break;

    case 'a':
      printf("You pressed the 'a' key.\n");
    break;

    default:
      break;
  }
}

// this function gets called continuously (alternates execution with "DoIdle")
void Display()					
{
  // clear the screen and the depth buffer
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);	

  // select the modelview matrix
  glMatrixMode(GL_MODELVIEW);						
  // clear the modelview matrix
  glLoadIdentity();									
  // set the camera position
  double cameraPosition[3] = {1.0, cameraHeight, 1.0};
  double focusPosition[3] = {0, 0, 0};
  double up[3] = {0,1,0};
  gluLookAt( cameraPosition[0], cameraPosition[1], cameraPosition[2],
    focusPosition[0], focusPosition[1], focusPosition[2],
    up[0], up[1], up[2]);

  // draw two triangles
  glBegin(GL_TRIANGLES);

    // === triangle 1 ===   
    // rotate the triangle along the y-axis

    // vertex 1
    // set the white color
    glColor3f(1, 1, 1);
    glVertex3f(0, 0, 0);

    // vertex 2
    // set the blue color
    glColor3f(0, 0, 1);
    glVertex3f(0, 0.2, 0); // vertex at (0, 0.2, 0)

    // vertex 3
    // set a weak hue of red
    glColor3f(0.2, 0, 0);
    glVertex3f(0.2 * cos(angle), 0, 0.2 * sin(angle));

    // === triangle 2 ===   

    // vertex 1
    // set the green color
    glColor3f(0, 1, 0);
    glVertex3f(0.2, 0, 0);

    // vertex 2
    // set black color
    glColor3f(0, 0, 0);
    glVertex3f(0.2, 0.2, 0);

    // vertex 3
    // set white color
    glColor3f(1, 1, 1);
    glVertex3f(0.4, 0, 0);

  glEnd();

  // render coordinate system axes
  glLineWidth(3.0); // set line width
  glBegin(GL_LINES);
  glColor3f(1,0,0);
    glVertex3f(0,0,0);
    glVertex3f(0.5,0,0);
  glColor3f(0,1,0);
    glVertex3f(0,0,0);
    glVertex3f(0,0.5,0);
  glColor3f(0,0,1);
    glVertex3f(0,0,0);
    glVertex3f(0,0,0.5);
  glEnd();

  // swap buffers 
  // warning: do not forget this call, or else nothing will be drawn
  glutSwapBuffers();
}

int main (int argc, char ** argv)
{
  // init GLUT
  glutInit(&argc,argv);
  
  // double buffering, use RGBA colors, use depth buffer
  glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH);

  // create a 400x400 window
  windowWidth = 400;
  windowHeight = 400;
  glutInitWindowSize (windowWidth,windowHeight);

  // init window position on the screen
  glutInitWindowPosition (0,0);

  // set the window title
  char s[4096] = "Hello world";
  windowID = glutCreateWindow(s);
  //glutFullScreen(); // make window full-screen

  // register the display callback
  glutDisplayFunc(Display);

  // register the reshape callback
  glutReshapeFunc(Reshape);

  // register the idle callback
  glutIdleFunc(DoIdle);

  // register the keyboard callback
  glutKeyboardFunc(KeyboardFunc);
 
  // call our initialization
  Init();

  // forever sink into an internal GLUT loop
  glutMainLoop();

  // we never reach this point
  return(0);
}