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

#define GL_GLEXT_PROTOTYPES 1
#include <GL/gl.h>
#include <GL/glut.h>

#define WINDSIZEX 300
#define WINDSIZEY 300

#define TRIANGLE_COUNT1 1
#define TRIANGLE_COUNT2 2
#define TRIANGLE_ARRAY_BYTES (sizeof (GLfloat) * 2 * 3 * TRIANGLE_COUNT1)

void
display (void)
{
  GLuint vbo_name;
  GLfloat *triangle_array1;
  GLfloat *triangle_array2;
  int i, v;

  triangle_array2 = malloc (sizeof (GLfloat) * 2 * 3 * TRIANGLE_COUNT2);

  glClearColor (0.0f, 0.0f, 0.0f, 0.0f);
  glClear (GL_COLOR_BUFFER_BIT);

  glEnableClientState (GL_VERTEX_ARRAY);

  glGenBuffers (1, &vbo_name);
  glBindBuffer (GL_ARRAY_BUFFER, vbo_name);
  glBufferData (GL_ARRAY_BUFFER, TRIANGLE_ARRAY_BYTES, NULL, GL_STATIC_DRAW);
  triangle_array1 = glMapBuffer (GL_ARRAY_BUFFER, GL_WRITE_ONLY);

  if (triangle_array1 == NULL) {
    fprintf (stderr, "Couldn't map VBO\n");
    exit (1);
  }

  v = 0;
  for (i = 0; i < TRIANGLE_COUNT1; i++) {                      //
    triangle_array1 [v++] = -1.;  triangle_array1 [v++] = -1.; //   /|
    triangle_array1 [v++] =  1.;  triangle_array1 [v++] = -1.; //  / |
    triangle_array1 [v++] =  1.;  triangle_array1 [v++] =  1.; // /__|
  }

  v = 0;
  for (i = 0; i < TRIANGLE_COUNT2; i++) {                      //  ___
    triangle_array2 [v++] = -1.;  triangle_array2 [v++] = -1.; // |  /
    triangle_array2 [v++] = -1.;  triangle_array2 [v++] =  1.; // | /
    triangle_array2 [v++] =  1.;  triangle_array2 [v++] =  1.; // |/
  }

  glUnmapBuffer (GL_ARRAY_BUFFER);
  glVertexPointer (2, GL_FLOAT, 0, NULL);
  glDrawArrays (GL_TRIANGLES, 0, 3 * TRIANGLE_COUNT1);
  triangle_array1 = glMapBuffer (GL_ARRAY_BUFFER, GL_WRITE_ONLY);

  /* START DELIBERATE BUG */
  glVertexPointer (2, GL_FLOAT, 0, triangle_array2);
  glDrawArrays (GL_POINTS, 0, 3 * TRIANGLE_COUNT2);
  glDisableClientState (GL_VERTEX_ARRAY);
  glDisable (GL_COLOR_LOGIC_OP);
  /* END DELIBARATE BUG */

  /* Not sure if this is needed, but it crashes with.. haven't tested without */
#if 1
  glGenBuffers (1, &vbo_name);
  glBindBuffer (GL_ARRAY_BUFFER, vbo_name);
  glBufferData (GL_ARRAY_BUFFER, TRIANGLE_ARRAY_BYTES, NULL, GL_STATIC_DRAW);
  triangle_array1 = glMapBuffer (GL_ARRAY_BUFFER, GL_WRITE_ONLY);

  v = 0;
  for (i = 0; i < TRIANGLE_COUNT1; i++) {                      //
    triangle_array1 [v++] = -1.;  triangle_array1 [v++] = -1.; //   /|
    triangle_array1 [v++] =  1.;  triangle_array1 [v++] = -1.; //  / |
    triangle_array1 [v++] =  1.;  triangle_array1 [v++] =  1.; // /__|
  }
#endif

  glVertexPointer (2, GL_FLOAT, 0, NULL);
  glDrawArrays (GL_TRIANGLES, 0, 3 * TRIANGLE_COUNT1);

  glBindBuffer (GL_ARRAY_BUFFER, 0);
  glDeleteBuffers (1, &vbo_name);

  glutSwapBuffers();
  free (triangle_array2);
}

int
main (int argc, char** argv)
{
  glutInit (&argc, argv);
  glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGB);
  glutInitWindowSize (WINDSIZEX, WINDSIZEY);
  glutCreateWindow (argv[0]);
  glutDisplayFunc (display);

  glMatrixMode (GL_PROJECTION);
  gluPerspective (/* field of view in degree */ 40.0,
                             /* aspect ratio */ 1.0,
                                   /* Z near */ 1.0,
                                   /* Z far */ 70.0);
  glMatrixMode(GL_MODELVIEW);
  gluLookAt (0.0, 0.0, 5.0,      /* eye is at (0,0,5) */
             0.0, 0.0, 0.0,      /* center is at (0,0,0) */
             0.0, 1.0, 0.);      /* up is in positive Y direction */

  glutMainLoop ();
  return 0;
}