#include <stdio.h>
#include <string.h>

#include <GL/glut.h>


void display(void);
void idle(void);
void reshape(int w, int h);
void keyboard(unsigned char key, int x, int y);

void draw_cube(void);
void game_mode(char *mode);
void dump_game_mode(void);
void init(void);
void on_exit(void);

float spin = 0;


void
draw_cube(void)
{
  glLoadIdentity();

  /* A step backward, then spin the cube */
  glTranslatef(0, 0, -5);
  glRotatef(spin, 0, 0, 1);
  glRotatef(spin, 1, 0.6, 0);

  /* We tell we want to draw quads */
  glBegin (GL_QUADS);

  /* Every four calls to glVertex, a quad is drawn */
  glColor3f(0, 0, 0); glVertex3f(-1, -1, -1);
  glColor3f(0, 0, 1); glVertex3f(-1, -1,  1);
  glColor3f(0, 1, 1); glVertex3f(-1,  1,  1);
  glColor3f(0, 1, 0); glVertex3f(-1,  1, -1);

  glColor3f(1, 0, 0); glVertex3f( 1, -1, -1);
  glColor3f(1, 0, 1); glVertex3f( 1, -1,  1);
  glColor3f(1, 1, 1); glVertex3f( 1,  1,  1);
  glColor3f(1, 1, 0); glVertex3f( 1,  1, -1);

  glColor3f(0, 0, 0); glVertex3f(-1, -1, -1);
  glColor3f(0, 0, 1); glVertex3f(-1, -1,  1);
  glColor3f(1, 0, 1); glVertex3f( 1, -1,  1);
  glColor3f(1, 0, 0); glVertex3f( 1, -1, -1);

  glColor3f(0, 1, 0); glVertex3f(-1,  1, -1);
  glColor3f(0, 1, 1); glVertex3f(-1,  1,  1);
  glColor3f(1, 1, 1); glVertex3f( 1,  1,  1);
  glColor3f(1, 1, 0); glVertex3f( 1,  1, -1);

  glColor3f(0, 0, 0); glVertex3f(-1, -1, -1);
  glColor3f(0, 1, 0); glVertex3f(-1,  1, -1);
  glColor3f(1, 1, 0); glVertex3f( 1,  1, -1);
  glColor3f(1, 0, 0); glVertex3f( 1, -1, -1);

  glColor3f(0, 0, 1); glVertex3f(-1, -1,  1);
  glColor3f(0, 1, 1); glVertex3f(-1,  1,  1);
  glColor3f(1, 1, 1); glVertex3f( 1,  1,  1);
  glColor3f(1, 0, 1); glVertex3f( 1, -1,  1);

  glEnd();
}


void
display(void)
{
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

  draw_cube();

  glutSwapBuffers();
}


void
idle(void)
{
        spin += 0.5;
        if (spin > 360.0)
                spin = 0.0;

        glutPostRedisplay();
}


void
reshape(int w, int h)
{
        glViewport (0, 0, (GLsizei) w, (GLsizei) h);
        // Setup the view of the cube.
        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        gluPerspective( /* field of view in degree */ 40.0,
                /* aspect ratio */ 1.0,
                /* Z near */ 1.0, /* Z far */ 10.0);
        glMatrixMode(GL_MODELVIEW);
        glLoadIdentity();
        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

        // Adjust cube position to be asthetic angle.
        glTranslatef(0.0, 0.0, -1.0);
        glRotatef(60, 1.0, 0.0, 0.0);
        glRotatef(-20, 0.0, 0.0, 1.0);
}


void
keyboard(unsigned char key, int x, int y)
{
        switch(key) {
                case 27:
                        exit(0);
                        break;

                case 'g':
                case 'G':
                        dump_game_mode();
                        break;

                case 'e':
                case 'E': {
                        char mode[255];

                        printf("Game mode string? ");
                        gets(mode);
                        if (!strlen(mode))
                                break;

                        game_mode(mode);
                        if (glutGameModeGet(GLUT_GAME_MODE_DISPLAY_CHANGED))
                                init();
                        break;
                }

                case 'l':
                case 'L': {
                        // return to default window
                        glutLeaveGameMode();
                        if (!glutGetWindow())
                                // exit if none
                                exit(0);
                        break;
                }
        }
}


void
init(void)
{
        glutIdleFunc(idle);
        glutDisplayFunc(display);
        glutReshapeFunc(reshape);
        glutKeyboardFunc(keyboard);

        glClearColor(0, 0, 0, 0);
        glEnable(GL_DEPTH_TEST);
}


void
on_exit(void)
{
        printf("Exit.\n");
}


void
game_mode(char *mode)
{
        glutGameModeString(mode);

        printf("glutGameModeString(\"%s\"): ", mode);
        if (!glutGameModeGet(GLUT_GAME_MODE_POSSIBLE)) {
                printf("*not* possible!\n");
                return;
        }

        printf("possible.\nglutEnterGameMode()\n");
        glutEnterGameMode();

        printf("glutGameModeGet(GLUT_GAME_MODE_DISPLAY_CHANGED) = %d\n",
                        glutGameModeGet(GLUT_GAME_MODE_DISPLAY_CHANGED));
}


void
dump_game_mode()
{
        printf("glutGameModeGet():\n");

#       define DUMP(pname)      \
        printf("\t" #pname " = %d\n", glutGameModeGet(pname));

        DUMP(GLUT_GAME_MODE_ACTIVE);
        DUMP(GLUT_GAME_MODE_POSSIBLE);
        DUMP(GLUT_GAME_MODE_WIDTH);
        DUMP(GLUT_GAME_MODE_HEIGHT);
        DUMP(GLUT_GAME_MODE_PIXEL_DEPTH);
        DUMP(GLUT_GAME_MODE_REFRESH_RATE);
        DUMP(GLUT_GAME_MODE_DISPLAY_CHANGED);

#       undef DUMP

        printf("\n");
}

int
main(int argc, char **argv)
{
        glutInit(&argc, argv);
        glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH);

        if (argc > 1)
                game_mode(argv[1]);

        if (!glutGameModeGet(GLUT_GAME_MODE_ACTIVE)) {
                printf("Using windowed mode.\n");
                glutCreateWindow(argv[0]);
        }

        init();

        atexit(on_exit);
        glutMainLoop();

        return 0;
}