/*
 * gcc -Wall -ansi -lGL -lGLU -lGLEW -lglut vbo.c -o vbo
 */

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

struct VN_t
{
  GLfloat v[3]; /* position */
  GLfloat n[3]; /* normal */
};

static struct VN_t cube[24] = {
  { { 0.0, 0.0, 0.0 }, { 0.0, 0.0, -1.0 } },
  { { 0.0, 1.0, 0.0 }, { 0.0, 0.0, -1.0 } },
  { { 1.0, 1.0, 0.0 }, { 0.0, 0.0, -1.0 } },
  { { 1.0, 0.0, 0.0 }, { 0.0, 0.0, -1.0 } },

  { { 0.0, 0.0, 1.0 }, { 0.0, 0.0, 1.0 } },
  { { 1.0, 0.0, 1.0 }, { 0.0, 0.0, 1.0 } },
  { { 1.0, 1.0, 1.0 }, { 0.0, 0.0, 1.0 } },
  { { 0.0, 1.0, 1.0 }, { 0.0, 0.0, 1.0 } },

  { { 1.0, 0.0, 1.0 }, { 1.0, 0.0, 0.0 } },
  { { 1.0, 0.0, 0.0 }, { 1.0, 0.0, 0.0 } },
  { { 1.0, 1.0, 0.0 }, { 1.0, 0.0, 0.0 } },
  { { 1.0, 1.0, 1.0 }, { 1.0, 0.0, 0.0 } },

  { { 0.0, 0.0, 1.0 }, { -1.0, 0.0, 0.0 } },
  { { 0.0, 1.0, 1.0 }, { -1.0, 0.0, 0.0 } },
  { { 0.0, 1.0, 0.0 }, { -1.0, 0.0, 0.0 } },
  { { 0.0, 0.0, 0.0 }, { -1.0, 0.0, 0.0 } },

  { { 0.0, 1.0, 1.0 }, { 0.0, 1.0, 0.0 } },
  { { 1.0, 1.0, 1.0 }, { 0.0, 1.0, 0.0 } },
  { { 1.0, 1.0, 0.0 }, { 0.0, 1.0, 0.0 } },
  { { 0.0, 1.0, 0.0 }, { 0.0, 1.0, 0.0 } },

  { { 0.0, 0.0, 1.0 }, { 0.0, -1.0, 0.0 } },
  { { 0.0, 0.0, 0.0 }, { 0.0, -1.0, 0.0 } },
  { { 1.0, 0.0, 0.0 }, { 0.0, -1.0, 0.0 } },
  { { 1.0, 0.0, 1.0 }, { 0.0, -1.0, 0.0 } },

};

static GLushort indices[24] = {
  0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,
  13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23
};

GLuint vboId = 0;
GLuint iboId = 0;

static void
init ()
{
  GLenum err = glewInit ();
  if (GLEW_OK != err)
    {
      /* Problem: glewInit failed, something is seriously wrong. */
      fprintf (stderr, "Error: %s\n", glewGetErrorString (err));
      exit (EXIT_FAILURE);
    }

  if (!GLEW_ARB_vertex_buffer_object)
    {
      fprintf (stderr, "Error: missing ARB_vertex_buffer_object extension\n");
      exit (EXIT_FAILURE);
    }

  /* OpenGL initialization */
  glClearColor (0.1f, 0.1f, 0.1f, 0.0f);
  glShadeModel (GL_SMOOTH);

  glEnable (GL_CULL_FACE);
  glEnable (GL_DEPTH_TEST);
  glEnable (GL_LIGHTING);
  glEnable (GL_LIGHT0);

  /* Here we create the VBOs. The index buffer object is made static,
     because we just want to test the mapping of the vertex buffer
     object. */
  glGenBuffersARB (1, &vboId);
  glGenBuffersARB (1, &iboId);

  /* Allocate and copy data for index buffer object */
  glBindBufferARB (GL_ELEMENT_ARRAY_BUFFER, iboId);
  glBufferDataARB (GL_ELEMENT_ARRAY_BUFFER, 24 * sizeof (GLushort), &indices, GL_STATIC_DRAW);

  /* Allocate memory for vertex buffer object */
  glBindBufferARB (GL_ARRAY_BUFFER, vboId);
  glBufferDataARB (GL_ARRAY_BUFFER, 24 * sizeof (struct VN_t), NULL, GL_STREAM_DRAW_ARB);

  glBindBufferARB (GL_ELEMENT_ARRAY_BUFFER, 0);
  glBindBufferARB (GL_ARRAY_BUFFER, 0);
}

static void
reshape (int w, int h)
{
  if (h == 0)
    h = 1;

  glViewport (0, 0, (GLsizei)w, (GLsizei)h);

  glMatrixMode (GL_PROJECTION);
  glLoadIdentity ();
  gluPerspective (45.0, (GLfloat)w/(GLfloat)h, 0.1, 1000.0);

  glMatrixMode (GL_MODELVIEW);
  glLoadIdentity ();

  glutPostRedisplay ();
}

static void
printMappingState (const char *s)
{
  GLint is_mapped = 0;
  glBindBufferARB (GL_ARRAY_BUFFER_ARB, vboId);
  glGetBufferParameterivARB (GL_ARRAY_BUFFER_ARB, GL_BUFFER_MAPPED_ARB, &is_mapped);
  printf ("%s, buffer is%s mapped\n", s, is_mapped ? "" : " not");
}

static void
display ()
{
  GLenum err;
  struct VN_t *v;
  static float angle = 25.0;
  static int frame = 1;

  glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

  /* Camera setup */
  glLoadIdentity ();
  glTranslated (0.0f, 0.0f, -3.0f);
  glRotated (35.0f, 1.0f, 0.0f, 0.0f);
  glRotated (angle, 0.0f, 1.0f, 0.0f);
  glTranslatef (-0.5f, -0.5f, -0.5f);

  angle += 0.2;

  glBindBufferARB (GL_ELEMENT_ARRAY_BUFFER, iboId);
  glBindBufferARB (GL_ARRAY_BUFFER, vboId);

  printMappingState ("Before copying data");

  if (0)
    {
      /* This code path works */
      glBufferDataARB (GL_ARRAY_BUFFER, 24 * sizeof (struct VN_t), &cube, GL_STREAM_DRAW_ARB);
    }
  else
    {
      /* This code path doesn't work, unless if we uncomment the
	 following line: */
      /*glBufferDataARB (GL_ARRAY_BUFFER, 24 * sizeof (struct vertex), NULL, GL_STREAM_DRAW_ARB);*/

      printf ("Mapping frame %i\n", frame);

      /* Map the buffer, copy data into it, and unmap it */
      v = (struct VN_t *)glMapBufferARB (GL_ARRAY_BUFFER_ARB, GL_WRITE_ONLY_ARB);
      memcpy (v, &cube, sizeof (cube));
      glUnmapBufferARB (GL_ARRAY_BUFFER_ARB);
    }

  glEnableClientState (GL_VERTEX_ARRAY);
  glEnableClientState (GL_NORMAL_ARRAY);

  printMappingState ("Before drawing");

  glNormalPointer (GL_FLOAT, sizeof (struct VN_t), (char *)(sizeof (GLfloat) * 3));
  glVertexPointer (3, GL_FLOAT, sizeof (struct VN_t), 0);

  glDrawElements (GL_QUADS, 24, GL_UNSIGNED_SHORT, 0);

  glBindBufferARB (GL_ELEMENT_ARRAY_BUFFER, 0);
  glBindBufferARB (GL_ARRAY_BUFFER, 0);

  glDisableClientState (GL_VERTEX_ARRAY);
  glDisableClientState (GL_NORMAL_ARRAY);

  printMappingState ("After drawing");

  err = glGetError ();
  if (err != GL_NO_ERROR)
    fprintf (stderr, "OpenGL error: %s\n", gluErrorString (err));

  printf ("Frame %i finished...\n----------\n", frame);
  frame++;

  glutSwapBuffers ();
  glutPostRedisplay ();
}

static void
keyPress (unsigned char key, int x, int y)
{
  /* Escape */
  if (key == 27)
    exit (0);

  glutPostRedisplay ();
}

int
main (int argc, char *argv[])
{
  glutInit (&argc, argv);

  glutInitDisplayMode (GLUT_RGBA | GLUT_DOUBLE | GLUT_DEPTH);
  glutInitWindowSize (640, 480);
  glutCreateWindow ("VBO demo");

  init ();

  glutReshapeFunc (reshape);
  glutDisplayFunc (display);
  glutKeyboardFunc (keyPress);

  glutMainLoop ();

  return 0;
}