// 
// OpenGL program to draw the XYZ axes of the world frame, and 
// a scaled wireframe cube positioned at the origin of the world frame.
//

#include <GL/glut.h>

void init()
{
  glClearColor(0.0, 0.0, 0.0, 0.0); // background color 
}

// callback function when window is reshaped
void reshape(int w, int h)
{
  glViewport(0, 0, w, h); // w and h are passed by GLUT

  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  // Perspective projection: fov (in y), aspect ratio, near, far
  gluPerspective(60.0, (float) w/h, 1.0, 20.0); 
  // Orthographic projection: left, right, bottom, top, near, far
  //  glOrtho(-2.0, 2.0, -2.0, 2.0, 1.0, 20.0); 

  glMatrixMode(GL_MODELVIEW);
}

// all routines to redraw scene
void display()
{
  glClear(GL_COLOR_BUFFER_BIT);

  glLoadIdentity();
  // viewing transformation, sets camera position, aim by specifying
  // eye coords, center coords, and up vector
  gluLookAt(0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);

  // draw world coordinate axes (useful for debugging)
  glLineWidth(2.0);
  glBegin(GL_LINES);
  // X axis, red 
  glColor3f(1.0, 0.0, 0.0);
  glVertex3f(0.0, 0.0, 0.0);
  glVertex3f(1.0, 0.0, 0.0);
  // Y axis, green
  glColor3f(0.0, 1.0, 0.0);
  glVertex3f(0.0, 0.0, 0.0);
  glVertex3f(0.0, 1.0, 0.0);
  // Z axis, blue
  glColor3f(0.0, 0.0, 1.0);
  glVertex3f(0.0, 0.0, 0.0);
  glVertex3f(0.0, 0.0, 1.0);
  glEnd();
  glLineWidth(1.0);

  glColor3f(1.0, 1.0, 1.0);
  glScalef(1.0, 3.0, 1.0); // scale cube by 3.0 along Y axis
  glutWireCube(1.0); // draw wireframe cube

  glFlush();
}

// input keyboard function to quit with q or Q.
void keyboard(unsigned char key, int x, int y)
{
  if (key == 'q' || key == 'Q')
    exit(0);
}

int main (int argc, char** argv)
{
  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE);
  glutInitWindowSize(400,400);  // width, height in pixels
  glutInitWindowPosition(400,0); // x, y from top left corner of screen
  glutCreateWindow(argv[0]); // program name is window title
  init();
  // register the callback functions
  glutReshapeFunc(reshape);
  glutKeyboardFunc(keyboard);
  glutDisplayFunc(display);
  glutMainLoop();

  return 0;
}