/* File: step1.c
   Author: Katia Oleinik

   This example demonstrates 

   - viewing clipping planes
   - perspective (glFrustum) and orthographic (glOrtho) views
   - setting up camera position
   - RGB colors
   - GLUT primitieves

   Solution to the Assignment: 
   1. Draw a ball of radius 1, with the color of your choice
   2. Set ortho proj., so that the diam. of the ball would be about 20% of the width of the screen. 
   3. Set camera on z axis 5 units away from the origin
*/

#include <stdio.h>
#include <stdlib.h>
#include <GL/glut.h>

void mydraw(void);
void display(void);
void init(void);

/* drawing routine, called by display every animated frame */
void mydraw(void)
{
  /* Set up red color */
  glColor3f( 1.0, 0.0, 0.0); // red color

  /* draw a sphere of radius 1.*/
  glutSolidSphere(1., 24, 24);
}

/* display is called by the glut main loop once for every animated frame */
void display(void)
{
  /* initialize color and depth buffers */
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

  /* call the routine that actually draws what you want */
  mydraw();

  /* show the just-filled frame buffer */
  glutSwapBuffers();
}

/* called once to set up basic opengl state */
void init(void)
{
  /* Use depth buffering for hidden surface elimination. */
  glEnable(GL_DEPTH_TEST);

  /* Set up the perspective matrix */
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();

  /* left, right, bottom, top, near, far */
  /* near and far values are the distances 
     from the camera to the front and rear clipping planes */
  glOrtho(-4.0, 4.0, -4.0, 4.0, 1., 10.0);  // orthgraphic view

  /* Set up the model view matrix */
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();

  /* Camera position */
  /* By the default, the camera is situated at the origin, points down the negative z-axis,
     and has an upper vector (0,1,0)*/
  gluLookAt(0.,0.,5.,0.,0.,0.,0.,1.,0.);
}

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

  /* GLUT Configuration */
  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);

  /* These setup calls are optional - set size and position of the window */
  glutInitWindowSize(500,500); 
  glutInitWindowPosition(100,100);

  /* Create Window */
  glutCreateWindow("Red ball");

  /* Set display as a callback for the current window */
  glutDisplayFunc(display);

  /* Set basic openGL states */
  init();

  /* Enter GLUT event processing loop, 
     which interprets events and calls respective callback routines */
  glutMainLoop();

  /* Exit the program */
  return 0;
}