progs/demos/terrain.c

   1 /*
   2  * This program is under the GNU GPL.
   3  * Use at your own risk.
   4  *
   5  * written by David Bucciarelli (tech.hmw@plus.it)
   6  *            Humanware s.r.l.
   7  *
   8  * based on a Mikael SkiZoWalker's (MoDEL) / France (Skizo@Hol.Fr) demo
   9  */
  10
  11 #include <assert.h>
  12 #include <stdio.h>
  13 #include <math.h>
  14 #include <stdlib.h>
  15 #include <string.h>
  16 #include <time.h>
  17
  18 #ifdef WIN32
  19 #include <windows.h>
  20 #endif
  21
  22 #include <GL/glut.h>
  23
  24 #ifdef XMESA
  25 #include "GL/xmesa.h"
  26 static int fullscreen = 1;
  27 #endif
  28
  29 #ifndef M_PI
  30 #define M_PI 3.14159265
  31 #endif
  32
  33 #define heightMnt       450
  34 #define lenghtXmnt      62
  35 #define lenghtYmnt      62
  36
  37 #define stepXmnt     96.0
  38 #define stepYmnt     96.0
  39
  40 #define WIDTH 640
  41 #define HEIGHT 480
  42
  43 static GLint T0 = 0;
  44 static GLint Frames = 0;
  45
  46 #define TSCALE 4
  47
  48 #define FOV 85
  49
  50 static GLfloat terrain[256 * 256];
  51 static GLfloat terraincolor[256 * 256][3];
  52
  53 static int win = 0;
  54
  55 static int fog = 1;
  56 static int bfcull = 1;
  57 static int usetex = 1;
  58 static int poutline = 0;
  59 static int help = 1;
  60 static int joyavailable = 0;
  61 static int joyactive = 0;
  62 static float ModZMnt;
  63 static long GlobalMnt = 0;
  64
  65 static int scrwidth = WIDTH;
  66 static int scrheight = HEIGHT;
  67
  68 #define OBSSTARTX 992.0
  69 #define OBSSTARTY 103.0
  70
  71 static float obs[3] = { OBSSTARTX, heightMnt * 1.3, OBSSTARTY };
  72 static float dir[3], v1[2], v2[2];
  73 static float v = 900.0;
  74 static float alpha = 75.0;
  75 static float beta = 90.0;
  76
  77 static void
  78 calcposobs(void)
  79 {
  80    float alpha1, alpha2;
  81    static double t0 = -1.;
  82    double dt, t = glutGet(GLUT_ELAPSED_TIME) / 1000.0;
  83    if (t0 < 0.0)
  84       t0 = t;
  85    dt = t - t0;
  86    t0 = t;
  87
  88    dir[0] = sin(alpha * M_PI / 180.0);
  89    dir[2] = cos(alpha * M_PI / 180.0) * sin(beta * M_PI / 180.0);
  90    dir[1] = cos(beta * M_PI / 180.0);
  91
  92    if (dir[0] < 1.0e-5 && dir[0] > -1.0e-5)
  93       dir[0] = 0;
  94    if (dir[1] < 1.0e-5 && dir[1] > -1.0e-5)
  95       dir[1] = 0;
  96    if (dir[2] < 1.0e-5 && dir[2] > -1.0e-5)
  97       dir[2] = 0;
  98
  99    alpha1 = alpha + FOV / 2.0;
 100    v1[0] = sin(alpha1 * M_PI / 180.0);
 101    v1[1] = cos(alpha1 * M_PI / 180.0);
 102
 103    alpha2 = alpha - FOV / 2.0;
 104    v2[0] = sin(alpha2 * M_PI / 180.0);
 105    v2[1] = cos(alpha2 * M_PI / 180.0);
 106
 107    obs[0] += v * dir[0] * dt;
 108    obs[1] += v * dir[1] * dt;
 109    obs[2] += v * dir[2] * dt;
 110
 111    if (obs[1] < 0.0)
 112       obs[1] = 0.0;
 113 }
 114
 115 static void
 116 reshape(int width, int height)
 117 {
 118    scrwidth = width;
 119    scrheight = height;
 120    glViewport(0, 0, (GLint) width, (GLint) height);
 121    glMatrixMode(GL_PROJECTION);
 122    glLoadIdentity();
 123    gluPerspective(50.0, ((GLfloat) width / (GLfloat) height),
 124                   lenghtXmnt * stepYmnt * 0.01, lenghtXmnt * stepYmnt * 0.7);
 125    glMatrixMode(GL_MODELVIEW);
 126    glLoadIdentity();
 127 }
 128
 129 static int
 130 clipstrip(float y, float *start, float *end)
 131 {
 132    float x1, x2, t1, t2, tmp;
 133
 134    if (v1[1] == 0.0) {
 135       t1 = 0.0;
 136       x1 = -HUGE_VAL;
 137    }
 138    else {
 139       t1 = y / v1[1];
 140       x1 = t1 * v1[0];
 141    }
 142
 143    if (v2[1] == 0.0) {
 144       t2 = 0.0;
 145       x2 = HUGE_VAL;
 146    }
 147    else {
 148       t2 = y / v2[1];
 149       x2 = t2 * v2[0];
 150    }
 151
 152    if (((x1 < -(lenghtXmnt * stepXmnt) / 2) && (t2 <= 0.0)) ||
 153        ((t1 <= 0.0) && (x2 > (lenghtXmnt * stepXmnt) / 2)) ||
 154        ((t1 < 0.0) && (t2 < 0.0)))
 155       return 0;
 156
 157    if ((t1 == 0.0) && (t2 == 0.0)) {
 158       if ((v1[0] < 0.0) && (v1[1] > 0.0) && (v2[0] < 0.0) && (v2[1] < 0.0)) {
 159          *start = -(lenghtXmnt * stepXmnt) / 2;
 160          *end = stepXmnt;
 161          return 1;
 162       }
 163       else {
 164          if ((v1[0] > 0.0) && (v1[1] < 0.0) && (v2[0] > 0.0) && (v2[1] > 0.0)) {
 165             *start = -stepXmnt;
 166             *end = (lenghtXmnt * stepXmnt) / 2;
 167             return 1;
 168          }
 169          else
 170             return 0;
 171       }
 172    }
 173    else {
 174       if (t2 < 0.0) {
 175          if (x1 < 0.0)
 176             x2 = -(lenghtXmnt * stepXmnt) / 2;
 177          else
 178             x2 = (lenghtXmnt * stepXmnt) / 2;
 179       }
 180
 181       if (t1 < 0.0) {
 182          if (x2 < 0.0)
 183             x1 = -(lenghtXmnt * stepXmnt) / 2;
 184          else
 185             x1 = (lenghtXmnt * stepXmnt) / 2;
 186       }
 187    }
 188
 189    if (x1 > x2) {
 190       tmp = x1;
 191       x1 = x2;
 192       x2 = tmp;
 193    }
 194
 195    x1 -= stepXmnt;
 196    if (x1 < -(lenghtXmnt * stepXmnt) / 2)
 197       x1 = -(lenghtXmnt * stepXmnt) / 2;
 198
 199    x2 += stepXmnt;
 200    if (x2 > (lenghtXmnt * stepXmnt) / 2)
 201       x2 = (lenghtXmnt * stepXmnt) / 2;
 202
 203    *start = ((int) (x1 / stepXmnt)) * stepXmnt;
 204    *end = ((int) (x2 / stepXmnt)) * stepXmnt;
 205
 206    return 1;
 207 }
 208
 209 static void
 210 printstring(void *font, char *string)
 211 {
 212    int len, i;
 213
 214    len = (int) strlen(string);
 215    for (i = 0; i < len; i++)
 216       glutBitmapCharacter(font, string[i]);
 217 }
 218
 219 static void
 220 printhelp(void)
 221 {
 222    glEnable(GL_BLEND);
 223    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
 224    glColor4f(0.0, 0.0, 0.0, 0.5);
 225    glRecti(40, 40, 600, 440);
 226    glDisable(GL_BLEND);
 227
 228    glColor3f(1.0, 0.0, 0.0);
 229    glRasterPos2i(300, 420);
 230    printstring(GLUT_BITMAP_TIMES_ROMAN_24, "Help");
 231
 232    glRasterPos2i(60, 390);
 233    printstring(GLUT_BITMAP_TIMES_ROMAN_24, "h - Toggle Help");
 234    glRasterPos2i(60, 360);
 235    printstring(GLUT_BITMAP_TIMES_ROMAN_24, "t - Toggle Textures");
 236    glRasterPos2i(60, 330);
 237    printstring(GLUT_BITMAP_TIMES_ROMAN_24, "f - Toggle Fog");
 238    glRasterPos2i(60, 300);
 239    printstring(GLUT_BITMAP_TIMES_ROMAN_24, "p - Wire frame");
 240    glRasterPos2i(60, 270);
 241    printstring(GLUT_BITMAP_TIMES_ROMAN_24, "b - Toggle Back face culling");
 242    glRasterPos2i(60, 240);
 243    printstring(GLUT_BITMAP_TIMES_ROMAN_24, "Arrow Keys - Rotate");
 244    glRasterPos2i(60, 210);
 245    printstring(GLUT_BITMAP_TIMES_ROMAN_24, "a - Increase velocity");
 246    glRasterPos2i(60, 180);
 247    printstring(GLUT_BITMAP_TIMES_ROMAN_24, "z - Decrease velocity");
 248
 249    glRasterPos2i(60, 150);
 250    if (joyavailable)
 251       printstring(GLUT_BITMAP_TIMES_ROMAN_24,
 252                   "j - Toggle jostick control (Joystick control available)");
 253    else
 254       printstring(GLUT_BITMAP_TIMES_ROMAN_24,
 255                   "(No Joystick control available)");
 256 }
 257
 258 static void
 259 drawterrain(void)
 260 {
 261    int h, i, idx, ox, oy;
 262    float j, k, start, end;
 263
 264    ox = (int) (obs[0] / stepXmnt);
 265    oy = (int) (obs[2] / stepYmnt);
 266    GlobalMnt = ((ox * TSCALE) & 255) + ((oy * TSCALE) & 255) * 256;
 267
 268    glPushMatrix();
 269    glTranslatef((float) ox * stepXmnt, 0, (float) oy * stepYmnt);
 270
 271    for (h = 0, k = -(lenghtYmnt * stepYmnt) / 2; h < lenghtYmnt;
 272         k += stepYmnt, h++) {
 273       if (!clipstrip(k, &start, &end))
 274          continue;
 275
 276       glBegin(GL_TRIANGLE_STRIP);       /* I hope that the optimizer will be able to improve this code */
 277       for (i = (int) (lenghtXmnt / 2 + start / stepXmnt), j = start; j <= end;
 278            j += stepXmnt, i++) {
 279          idx = (i * TSCALE + h * 256 * TSCALE + GlobalMnt) & 65535;
 280          glColor3fv(terraincolor[idx]);
 281          glTexCoord2f((ox + i) / 8.0, (oy + h) / 8.0);
 282          glVertex3f(j, terrain[idx], k);
 283
 284          idx =
 285             (i * TSCALE + h * 256 * TSCALE + 256 * TSCALE +
 286              GlobalMnt) & 65535;
 287          glColor3fv(terraincolor[idx]);
 288          glTexCoord2f((ox + i) / 8.0, (oy + h + 1) / 8.0);
 289          glVertex3f(j, terrain[idx], k + stepYmnt);
 290       }
 291       glEnd();
 292    }
 293
 294    glDisable(GL_CULL_FACE);
 295    glDisable(GL_TEXTURE_2D);
 296    glEnable(GL_BLEND);
 297    glBegin(GL_QUADS);
 298    glColor4f(0.1, 0.7, 1.0, 0.4);
 299    glVertex3f(-(lenghtXmnt * stepXmnt) / 2.0, heightMnt * 0.6,
 300               -(lenghtYmnt * stepYmnt) / 2.0);
 301    glVertex3f(-(lenghtXmnt * stepXmnt) / 2.0, heightMnt * 0.6,
 302               (lenghtYmnt * stepYmnt) / 2.0);
 303    glVertex3f((lenghtXmnt * stepXmnt) / 2.0, heightMnt * 0.6,
 304               (lenghtYmnt * stepYmnt) / 2.0);
 305    glVertex3f((lenghtXmnt * stepXmnt) / 2.0, heightMnt * 0.6,
 306               -(lenghtYmnt * stepYmnt) / 2.0);
 307    glEnd();
 308    glDisable(GL_BLEND);
 309    if (bfcull)
 310       glEnable(GL_CULL_FACE);
 311    glEnable(GL_TEXTURE_2D);
 312
 313    glPopMatrix();
 314
 315 }
 316
 317 static void
 318 dojoy(void)
 319 {
 320 #ifdef WIN32
 321    static UINT max[2] = { 0, 0 };
 322    static UINT min[2] = { 0xffffffff, 0xffffffff }, center[2];
 323    MMRESULT res;
 324    JOYINFO joy;
 325
 326    res = joyGetPos(JOYSTICKID1, &joy);
 327
 328    if (res == JOYERR_NOERROR) {
 329       joyavailable = 1;
 330
 331       if (max[0] < joy.wXpos)
 332          max[0] = joy.wXpos;
 333       if (min[0] > joy.wXpos)
 334          min[0] = joy.wXpos;
 335       center[0] = (max[0] + min[0]) / 2;
 336
 337       if (max[1] < joy.wYpos)
 338          max[1] = joy.wYpos;
 339       if (min[1] > joy.wYpos)
 340          min[1] = joy.wYpos;
 341       center[1] = (max[1] + min[1]) / 2;
 342
 343       if (joyactive) {
 344          if (fabs(center[0] - (float) joy.wXpos) > 0.1 * (max[0] - min[0]))
 345             alpha +=
 346                2.5 * (center[0] - (float) joy.wXpos) / (max[0] - min[0]);
 347          if (fabs(center[1] - (float) joy.wYpos) > 0.1 * (max[1] - min[1]))
 348             beta += 2.5 * (center[1] - (float) joy.wYpos) / (max[1] - min[1]);
 349
 350          if (joy.wButtons & JOY_BUTTON1)
 351             v += 0.5;
 352          if (joy.wButtons & JOY_BUTTON2)
 353             v -= 0.5;
 354       }
 355    }
 356    else
 357       joyavailable = 0;
 358 #endif
 359 }
 360
 361 static void
 362 drawscene(void)
 363 {
 364    static char frbuf[80] = "";
 365
 366    dojoy();
 367
 368    glShadeModel(GL_SMOOTH);
 369    glEnable(GL_DEPTH_TEST);
 370
 371    if (usetex)
 372       glEnable(GL_TEXTURE_2D);
 373    else
 374       glDisable(GL_TEXTURE_2D);
 375
 376    if (fog)
 377       glEnable(GL_FOG);
 378    else
 379       glDisable(GL_FOG);
 380
 381    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 382
 383    glPushMatrix();
 384
 385    calcposobs();
 386    gluLookAt(obs[0], obs[1], obs[2],
 387              obs[0] + dir[0], obs[1] + dir[1], obs[2] + dir[2],
 388              0.0, 1.0, 0.0);
 389
 390    drawterrain();
 391    glPopMatrix();
 392
 393    glDisable(GL_TEXTURE_2D);
 394    glDisable(GL_DEPTH_TEST);
 395    glDisable(GL_FOG);
 396    glShadeModel(GL_FLAT);
 397
 398    glMatrixMode(GL_PROJECTION);
 399    glLoadIdentity();
 400    glOrtho(-0.5, 639.5, -0.5, 479.5, -1.0, 1.0);
 401    glMatrixMode(GL_MODELVIEW);
 402    glLoadIdentity();
 403
 404    glColor3f(1.0, 0.0, 0.0);
 405    glRasterPos2i(10, 10);
 406    printstring(GLUT_BITMAP_HELVETICA_18, frbuf);
 407    glRasterPos2i(350, 470);
 408    printstring(GLUT_BITMAP_HELVETICA_10,
 409                "Terrain V1.2 Written by David Bucciarelli (tech.hmw@plus.it)");
 410    glRasterPos2i(434, 457);
 411    printstring(GLUT_BITMAP_HELVETICA_10,
 412                "Based on a Mickael's demo (Skizo@Hol.Fr)");
 413
 414    if (help)
 415       printhelp();
 416
 417    reshape(scrwidth, scrheight);
 418
 419    glutSwapBuffers();
 420
 421    Frames++;
 422    {
 423       GLint t = glutGet(GLUT_ELAPSED_TIME);
 424       if (t - T0 >= 2000) {
 425          GLfloat seconds = (t - T0) / 1000.0;
 426          GLfloat fps = Frames / seconds;
 427          sprintf(frbuf, "Frame rate: %f", fps);
 428          T0 = t;
 429          Frames = 0;
 430       }
 431    }
 432 }
 433
 434 static void
 435 key(unsigned char k, int x, int y)
 436 {
 437    switch (k) {
 438    case 27:
 439       exit(0);
 440       break;
 441    case 'a':
 442       v += 50.;
 443       break;
 444    case 'z':
 445       v -= 50.;
 446       break;
 447    case 'p':
 448       if (poutline) {
 449          glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);
 450          poutline = 0;
 451       }
 452       else {
 453          glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
 454          poutline = 1;
 455       }
 456       break;
 457    case 'j':
 458       joyactive = (!joyactive);
 459       break;
 460    case 'h':
 461       help = (!help);
 462       break;
 463    case 'f':
 464       fog = (!fog);
 465       break;
 466    case 't':
 467       usetex = (!usetex);
 468       break;
 469    case 'b':
 470       if (bfcull) {
 471          glDisable(GL_CULL_FACE);
 472          bfcull = 0;
 473       }
 474       else {
 475          glEnable(GL_CULL_FACE);
 476          bfcull = 1;
 477       }
 478       break;
 479 #ifdef XMESA
 480    case ' ':
 481       XMesaSetFXmode(fullscreen ? XMESA_FX_FULLSCREEN : XMESA_FX_WINDOW);
 482       fullscreen = (!fullscreen);
 483       break;
 484 #endif
 485    }
 486 }
 487
 488 static void
 489 special(int k, int x, int y)
 490 {
 491    switch (k) {
 492    case GLUT_KEY_LEFT:
 493       alpha += 2.0;
 494       break;
 495    case GLUT_KEY_RIGHT:
 496       alpha -= 2.0;
 497       break;
 498    case GLUT_KEY_DOWN:
 499       beta -= 2.0;
 500       break;
 501    case GLUT_KEY_UP:
 502       beta += 2.0;
 503       break;
 504    }
 505 }
 506
 507 static void
 508 calccolor(GLfloat height, GLfloat c[3])
 509 {
 510    GLfloat color[4][3] = {
 511       {1.0, 1.0, 1.0},
 512       {0.0, 0.8, 0.0},
 513       {1.0, 1.0, 0.3},
 514       {0.0, 0.0, 0.8}
 515    };
 516    GLfloat fact;
 517
 518    height = height * (1.0 / 255.0);
 519
 520    if (height >= 0.9) {
 521       c[0] = color[0][0];
 522       c[1] = color[0][1];
 523       c[2] = color[0][2];
 524       return;
 525    }
 526
 527    if ((height < 0.9) && (height >= 0.7)) {
 528       fact = (height - 0.7) * 5.0;
 529       c[0] = fact * color[0][0] + (1.0 - fact) * color[1][0];
 530       c[1] = fact * color[0][1] + (1.0 - fact) * color[1][1];
 531       c[2] = fact * color[0][2] + (1.0 - fact) * color[1][2];
 532       return;
 533    }
 534
 535    if ((height < 0.7) && (height >= 0.6)) {
 536       fact = (height - 0.6) * 10.0;
 537       c[0] = fact * color[1][0] + (1.0 - fact) * color[2][0];
 538       c[1] = fact * color[1][1] + (1.0 - fact) * color[2][1];
 539       c[2] = fact * color[1][2] + (1.0 - fact) * color[2][2];
 540       return;
 541    }
 542
 543    if ((height < 0.6) && (height >= 0.5)) {
 544       fact = (height - 0.5) * 10.0;
 545       c[0] = fact * color[2][0] + (1.0 - fact) * color[3][0];
 546       c[1] = fact * color[2][1] + (1.0 - fact) * color[3][1];
 547       c[2] = fact * color[2][2] + (1.0 - fact) * color[3][2];
 548       return;
 549    }
 550
 551    c[0] = color[3][0];
 552    c[1] = color[3][1];
 553    c[2] = color[3][2];
 554 }
 555
 556 static void
 557 loadpic(void)
 558 {
 559    GLubyte bufferter[256 * 256], terrainpic[256 * 256];
 560    FILE *FilePic;
 561    int i, tmp;
 562    GLenum gluerr;
 563    size_t result;
 564
 565    if ((FilePic = fopen("terrain.dat", "r")) == NULL) {
 566       fprintf(stderr, "Error loading terrain.dat\n");
 567       exit(-1);
 568    }
 569    result = fread(bufferter, 256 * 256, 1, FilePic);
 570    assert(result == 1);
 571    fclose(FilePic);
 572
 573    for (i = 0; i < (256 * 256); i++) {
 574       terrain[i] = (bufferter[i] * (heightMnt / 255.0f));
 575       calccolor((GLfloat) bufferter[i], terraincolor[i]);
 576       tmp = (((int) bufferter[i]) + 96);
 577       terrainpic[i] = (tmp > 255) ? 255 : tmp;
 578    }
 579
 580    glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
 581    if ((gluerr = gluBuild2DMipmaps(GL_TEXTURE_2D, 1, 256, 256, GL_LUMINANCE,
 582                                    GL_UNSIGNED_BYTE,
 583                                    (GLvoid *) (&terrainpic[0])))) {
 584       fprintf(stderr, "GLULib%s\n", (char *) gluErrorString(gluerr));
 585       exit(-1);
 586    }
 587
 588    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);
 589    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
 590
 591    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER,
 592                    GL_LINEAR_MIPMAP_LINEAR);
 593    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
 594
 595    glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
 596    glEnable(GL_TEXTURE_2D);
 597 }
 598
 599 static void
 600 init(void)
 601 {
 602    float fogcolor[4] = { 0.6, 0.7, 0.7, 1.0 };
 603
 604    glClearColor(fogcolor[0], fogcolor[1], fogcolor[2], fogcolor[3]);
 605    glClearDepth(1.0);
 606    glDepthFunc(GL_LEQUAL);
 607    glShadeModel(GL_SMOOTH);
 608    glEnable(GL_DEPTH_TEST);
 609    glEnable(GL_CULL_FACE);
 610
 611    glDisable(GL_BLEND);
 612    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
 613
 614    glEnable(GL_FOG);
 615    glFogi(GL_FOG_MODE, GL_EXP2);
 616    glFogfv(GL_FOG_COLOR, fogcolor);
 617    glFogf(GL_FOG_DENSITY, 0.0007);
 618 #ifdef FX
 619    glHint(GL_FOG_HINT, GL_NICEST);
 620 #endif
 621
 622    reshape(scrwidth, scrheight);
 623 }
 624
 625
 626 int
 627 main(int ac, char **av)
 628 {
 629    glutInitWindowSize(WIDTH, HEIGHT);
 630    glutInit(&ac, av);
 631
 632    glutInitDisplayMode(GLUT_RGB | GLUT_DEPTH | GLUT_DOUBLE);
 633
 634    if (!(win = glutCreateWindow("Terrain"))) {
 635       fprintf(stderr, "Error, couldn't open window\n");
 636       return -1;
 637    }
 638
 639    ModZMnt = 0.0f;
 640    loadpic();
 641
 642    init();
 643
 644 #ifndef FX
 645    glDisable(GL_TEXTURE_2D);
 646    usetex = 0;
 647 #endif
 648
 649    glutReshapeFunc(reshape);
 650    glutDisplayFunc(drawscene);
 651    glutKeyboardFunc(key);
 652    glutSpecialFunc(special);
 653    glutIdleFunc(drawscene);
 654
 655    glutMainLoop();
 656
 657    return 0;
 658 }