Monday, October 10, 2011

LD_PRELOAD ile Fonksiyon Yakalamak

Linux'ta isleyen herhangi bir kodun ic fonksiyonlarinin yerine bir baskasini gecirmek icin kullanilan bir teknik fonksiyon bindirme (function interposition). Kullanim soyle:

LD_PRELOAD=`pwd`/bizim-kodlar.so ./demo.exe

Dinamik kutuphane bizim-kodlar.so icinde derlenmis C/++ kodlari var. LD_PRELOAD degiskeni bir cevre degiskeni, ve orada tanimlanan kutuphaneler, diger tum kutuphanelere gore oncelik kazanir, yani once LD_PRELOAD'da tanimli kodlar isletiliyor. Cengel takmak icin o yuzden bicilmis kaftan.

Ornek: OpenGL kutuphanesinin ekrana bastigi goruntuyu yakalamak mesela, ekrana cizilen goruntuler glXSwapBuffers cagrisi yaparlar, bu cagri yerine kendi yazdigimiz bir fonksiyonu gecirip, esas fonksiyona aktarma yapmadan once arada goruntuyu alip bir dosyaya yazabiliriz. Alttaki kod demo.cpp basit bir OpenGL ornegi, bir objeyi alip surekli donduruyor. Bu cizimi, bindirilmis yeni fonksiyon uzerinden isletince, goruntunun kare kare ciktisi bir imaj dosyasi olarak /tmp altinda yazilacak.

make.sh

# sudo apt-get install freeglut3 freeglut3-dev libglew1.5 libglew1.5-dev libglu1-mesa libglu1-mesa-dev libgl1-mesa-glx libgl1-mesa-dev
g++ -o demo.exe demo.cpp -lglut -lGL -lGLU -lGLEW
gcc -shared -fPIC -o glcapture.so glcapture.c -ldl

load.sh

rm /tmp/*.tga
rm /tmp/*.jpg
LD_PRELOAD=`pwd`/glcapture.so ./demo.exe 

glcapture.c

/*
 * Use something like this:
 *
 * gcc -shared -fPIC -o glcapture.so glcapture.c -ldl
 * LD_PRELOAD=`pwd`/glcapture.so ./demo
 */

#include
#include
#include
#include
#include

#ifndef RTLD_NEXT
#define RTLD_NEXT ((void *) -1l)
#endif

#define WIDTH 640
#define HEIGHT 480
#define FPS 4

static char buf[WIDTH * HEIGHT * 3];
static int frameno = 0;

void glXSwapBuffers( Display *dpy, GLXDrawable drawable )
{
  printf("swap\n");
  void (*real_swap)(Display*, GLXDrawable);
  real_swap = (void(*)(Display*, GLXDrawable))dlsym(RTLD_NEXT, "glXSwapBuffers");

  FILE *ppm;
  char filename[256];
  glReadPixels(0, 0, WIDTH, HEIGHT, GL_BGR, GL_UNSIGNED_BYTE, buf);

  sprintf(filename, "/tmp/frame%05u.tga", frameno++);
  ppm = fopen(filename, "w");
  fwrite("\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00", 12, 1, ppm);
  {
    unsigned short w = WIDTH;
    fwrite(&w, 2, 1, ppm);
  }
  {
    unsigned short h = HEIGHT;
    fwrite(&h, 2, 1, ppm);
  }
  fwrite("\x18\x00", 2, 1, ppm);
  fwrite(buf, WIDTH*HEIGHT*3, 1, ppm);
  fclose(ppm);

  real_swap(dpy, drawable);
}

int gettimeofday(struct timeval *tv, struct timezone *tz)
{
  printf("gettimeofday frame %u\n", frameno);
  //tv->tv_sec = frameno / FPS;
  //tv->tv_usec = ((double)(frameno % FPS) / FPS) * 1000000;
  return 0;
}

int clock_gettime(clockid_t clk_id, struct timespec *tp)
{
  //tp->tv_sec = frameno / FPS;
  //tp->tv_nsec = ((double)(frameno % FPS) / FPS) * 1e9;
  return 0;
}

demo.cpp

#include
#include
#include
#include
#include

static int useRGB = 1;
static int useLighting = 1;
static int useFog = 0;
static int useDB = 1;
static int useLogo = 0;
static int useQuads = 1;

static int tick = -1;
static int moving = 1;

#define GREY 0
#define RED 1
#define GREEN 2
#define BLUE 3
#define CYAN 4
#define MAGENTA 5
#define YELLOW 6
#define BLACK 7

static float materialColor[8][4] =
{
  {0.8, 0.8, 0.8, 1.0},
  {0.8, 0.0, 0.0, 1.0},
  {0.0, 0.8, 0.0, 1.0},
  {0.0, 0.0, 0.8, 1.0},
  {0.0, 0.8, 0.8, 1.0},
  {0.8, 0.0, 0.8, 1.0},
  {0.8, 0.8, 0.0, 1.0},
  {0.0, 0.0, 0.0, 0.6},
};

static float lightPos[4] =
{2.0, 4.0, 2.0, 1.0};
#if 0
static float lightDir[4] =
{-2.0, -4.0, -2.0, 1.0};
#endif
static float lightAmb[4] =
{0.2, 0.2, 0.2, 1.0};
static float lightDiff[4] =
{0.8, 0.8, 0.8, 1.0};
static float lightSpec[4] =
{0.4, 0.4, 0.4, 1.0};

static float groundPlane[4] =
{0.0, 1.0, 0.0, 1.499};
static float backPlane[4] =
{0.0, 0.0, 1.0, 0.899};

static float fogColor[4] =
{0.0, 0.0, 0.0, 0.0};
static float fogIndex[1] =
{0.0};

static unsigned char shadowPattern[128] =
{
  0xaa, 0xaa, 0xaa, 0xaa, 0x55, 0x55, 0x55, 0x55,  /* 50% Grey */
  0xaa, 0xaa, 0xaa, 0xaa, 0x55, 0x55, 0x55, 0x55,
  0xaa, 0xaa, 0xaa, 0xaa, 0x55, 0x55, 0x55, 0x55,
  0xaa, 0xaa, 0xaa, 0xaa, 0x55, 0x55, 0x55, 0x55,
  0xaa, 0xaa, 0xaa, 0xaa, 0x55, 0x55, 0x55, 0x55,
  0xaa, 0xaa, 0xaa, 0xaa, 0x55, 0x55, 0x55, 0x55,
  0xaa, 0xaa, 0xaa, 0xaa, 0x55, 0x55, 0x55, 0x55,
  0xaa, 0xaa, 0xaa, 0xaa, 0x55, 0x55, 0x55, 0x55,
  0xaa, 0xaa, 0xaa, 0xaa, 0x55, 0x55, 0x55, 0x55,
  0xaa, 0xaa, 0xaa, 0xaa, 0x55, 0x55, 0x55, 0x55,
  0xaa, 0xaa, 0xaa, 0xaa, 0x55, 0x55, 0x55, 0x55,
  0xaa, 0xaa, 0xaa, 0xaa, 0x55, 0x55, 0x55, 0x55,
  0xaa, 0xaa, 0xaa, 0xaa, 0x55, 0x55, 0x55, 0x55,
  0xaa, 0xaa, 0xaa, 0xaa, 0x55, 0x55, 0x55, 0x55,
  0xaa, 0xaa, 0xaa, 0xaa, 0x55, 0x55, 0x55, 0x55,
  0xaa, 0xaa, 0xaa, 0xaa, 0x55, 0x55, 0x55, 0x55
};

static unsigned char sgiPattern[128] =
{
  0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,  /* SGI Logo */
  0xff, 0xbd, 0xff, 0x83, 0xff, 0x5a, 0xff, 0xef,
  0xfe, 0xdb, 0x7f, 0xef, 0xfd, 0xdb, 0xbf, 0xef,
  0xfb, 0xdb, 0xdf, 0xef, 0xf7, 0xdb, 0xef, 0xef,
  0xfb, 0xdb, 0xdf, 0xef, 0xfd, 0xdb, 0xbf, 0x83,
  0xce, 0xdb, 0x73, 0xff, 0xb7, 0x5a, 0xed, 0xff,
  0xbb, 0xdb, 0xdd, 0xc7, 0xbd, 0xdb, 0xbd, 0xbb,
  0xbe, 0xbd, 0x7d, 0xbb, 0xbf, 0x7e, 0xfd, 0xb3,
  0xbe, 0xe7, 0x7d, 0xbf, 0xbd, 0xdb, 0xbd, 0xbf,
  0xbb, 0xbd, 0xdd, 0xbb, 0xb7, 0x7e, 0xed, 0xc7,
  0xce, 0xdb, 0x73, 0xff, 0xfd, 0xdb, 0xbf, 0xff,
  0xfb, 0xdb, 0xdf, 0x87, 0xf7, 0xdb, 0xef, 0xfb,
  0xf7, 0xdb, 0xef, 0xfb, 0xfb, 0xdb, 0xdf, 0xfb,
  0xfd, 0xdb, 0xbf, 0xc7, 0xfe, 0xdb, 0x7f, 0xbf,
  0xff, 0x5a, 0xff, 0xbf, 0xff, 0xbd, 0xff, 0xc3,
  0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff
};

static float cube_vertexes[6][4][4] =
{
  {
    {-1.0, -1.0, -1.0, 1.0},
    {-1.0, -1.0, 1.0, 1.0},
    {-1.0, 1.0, 1.0, 1.0},
    {-1.0, 1.0, -1.0, 1.0}},

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

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

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

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

  {
    {1.0, 1.0, 1.0, 1.0},
    {-1.0, 1.0, 1.0, 1.0},
    {-1.0, -1.0, 1.0, 1.0},
    {1.0, -1.0, 1.0, 1.0}}
};

static float cube_normals[6][4] =
{
  {-1.0, 0.0, 0.0, 0.0},
  {1.0, 0.0, 0.0, 0.0},
  {0.0, -1.0, 0.0, 0.0},
  {0.0, 1.0, 0.0, 0.0},
  {0.0, 0.0, -1.0, 0.0},
  {0.0, 0.0, 1.0, 0.0}
};

static void
usage(void)
{
  printf("\n");
  printf("usage: scube [options]\n");
  printf("\n");
  printf("    display a spinning cube and its shadow\n");
  printf("\n");
  printf("  Options:\n");
  printf("    -geometry  window size and location\n");
  printf("    -c         toggle color index mode\n");
  printf("    -l         toggle lighting\n");
  printf("    -f         toggle fog\n");
  printf("    -db        toggle double buffering\n");
  printf("    -logo      toggle sgi logo for the shadow pattern\n");
  printf("    -quads     toggle use of GL_QUADS to draw the checkerboard\n");
  printf("\n");
#ifndef EXIT_FAILURE    /* should be defined by ANSI C
                            */
#define EXIT_FAILURE 1
#endif
  exit(EXIT_FAILURE);
}

void
buildColormap(void)
{
  if (useRGB) {
    return;
  } else {
    int mapSize = 1 << glutGet(GLUT_WINDOW_BUFFER_SIZE);
    int rampSize = mapSize / 8;
    int entry;
    int i;

    for (entry = 0; entry < mapSize; ++entry) {
      int hue = entry / rampSize;
      GLfloat val = (entry % rampSize) * (1.0 / (rampSize - 1));
      GLfloat red, green, blue;

      red = (hue == 0 || hue == 1 || hue == 5 || hue == 6) ? val : 0;
      green = (hue == 0 || hue == 2 || hue == 4 || hue == 6) ? val : 0;
      blue = (hue == 0 || hue == 3 || hue == 4 || hue == 5) ? val : 0;

      glutSetColor(entry, red, green, blue);
    }

    for (i = 0; i < 8; ++i) {
      materialColor[i][0] = i * rampSize + 0.2 * (rampSize - 1);
      materialColor[i][1] = i * rampSize + 0.8 * (rampSize - 1);
      materialColor[i][2] = i * rampSize + 1.0 * (rampSize - 1);
      materialColor[i][3] = 0.0;
    }

    fogIndex[0] = -0.2 * (rampSize - 1);
  }
}

static void
setColor(int c)
{
  if (useLighting) {
    if (useRGB) {
      glMaterialfv(GL_FRONT_AND_BACK,
        GL_AMBIENT_AND_DIFFUSE, &materialColor[c][0]);
    } else {
      glMaterialfv(GL_FRONT_AND_BACK,
        GL_COLOR_INDEXES, &materialColor[c][0]);
    }
  } else {
    if (useRGB) {
      glColor4fv(&materialColor[c][0]);
    } else {
      glIndexf(materialColor[c][1]);
    }
  }
}

static void
drawCube(int color)
{
  int i;

  setColor(color);

  for (i = 0; i < 6; ++i) {
    glNormal3fv(&cube_normals[i][0]);
    glBegin(GL_POLYGON);
    glVertex4fv(&cube_vertexes[i][0][0]);
    glVertex4fv(&cube_vertexes[i][1][0]);
    glVertex4fv(&cube_vertexes[i][2][0]);
    glVertex4fv(&cube_vertexes[i][3][0]);
    glEnd();
  }
}

static void
drawCheck(int w, int h, int evenColor, int oddColor)
{
  static int initialized = 0;
  static int usedLighting = 0;
  static GLuint checklist = 0;

  if (!initialized || (usedLighting != useLighting)) {
    static float square_normal[4] =
    {0.0, 0.0, 1.0, 0.0};
    static float square[4][4];
    int i, j;

    if (!checklist) {
      checklist = glGenLists(1);
    }
    glNewList(checklist, GL_COMPILE_AND_EXECUTE);

    if (useQuads) {
      glNormal3fv(square_normal);
      glBegin(GL_QUADS);
    }
    for (j = 0; j < h; ++j) {
      for (i = 0; i < w; ++i) {
        square[0][0] = -1.0 + 2.0 / w * i;
        square[0][1] = -1.0 + 2.0 / h * (j + 1);
        square[0][2] = 0.0;
        square[0][3] = 1.0;

        square[1][0] = -1.0 + 2.0 / w * i;
        square[1][1] = -1.0 + 2.0 / h * j;
        square[1][2] = 0.0;
        square[1][3] = 1.0;

        square[2][0] = -1.0 + 2.0 / w * (i + 1);
        square[2][1] = -1.0 + 2.0 / h * j;
        square[2][2] = 0.0;
        square[2][3] = 1.0;

        square[3][0] = -1.0 + 2.0 / w * (i + 1);
        square[3][1] = -1.0 + 2.0 / h * (j + 1);
        square[3][2] = 0.0;
        square[3][3] = 1.0;

        if (i & 1 ^ j & 1) {
          setColor(oddColor);
        } else {
          setColor(evenColor);
        }

        if (!useQuads) {
          glBegin(GL_POLYGON);
        }
        glVertex4fv(&square[0][0]);
        glVertex4fv(&square[1][0]);
        glVertex4fv(&square[2][0]);
        glVertex4fv(&square[3][0]);
        if (!useQuads) {
          glEnd();
        }
      }
    }

    if (useQuads) {
      glEnd();
    }
    glEndList();

    initialized = 1;
    usedLighting = useLighting;
  } else {
    glCallList(checklist);
  }
}

static void
myShadowMatrix(float ground[4], float light[4])
{
  float dot;
  float shadowMat[4][4];

  dot = ground[0] * light[0] +
    ground[1] * light[1] +
    ground[2] * light[2] +
    ground[3] * light[3];

  shadowMat[0][0] = dot - light[0] * ground[0];
  shadowMat[1][0] = 0.0 - light[0] * ground[1];
  shadowMat[2][0] = 0.0 - light[0] * ground[2];
  shadowMat[3][0] = 0.0 - light[0] * ground[3];

  shadowMat[0][1] = 0.0 - light[1] * ground[0];
  shadowMat[1][1] = dot - light[1] * ground[1];
  shadowMat[2][1] = 0.0 - light[1] * ground[2];
  shadowMat[3][1] = 0.0 - light[1] * ground[3];

  shadowMat[0][2] = 0.0 - light[2] * ground[0];
  shadowMat[1][2] = 0.0 - light[2] * ground[1];
  shadowMat[2][2] = dot - light[2] * ground[2];
  shadowMat[3][2] = 0.0 - light[2] * ground[3];

  shadowMat[0][3] = 0.0 - light[3] * ground[0];
  shadowMat[1][3] = 0.0 - light[3] * ground[1];
  shadowMat[2][3] = 0.0 - light[3] * ground[2];
  shadowMat[3][3] = dot - light[3] * ground[3];

  glMultMatrixf((const GLfloat *) shadowMat);
}

static char *windowNameRGBDB = "shadow cube (OpenGL RGB DB)";
static char *windowNameRGB = "shadow cube (OpenGL RGB)";
static char *windowNameIndexDB = "shadow cube (OpenGL Index DB)";
static char *windowNameIndex = "shadow cube (OpenGL Index)";

void
idle(void)
{
  tick++;
  if (tick >= 120) {
    tick = 0;
  }
  glutPostRedisplay();
}

/* ARGSUSED1 */
void
keyboard(unsigned char ch, int x, int y)
{
  switch (ch) {
  case 27:             /* escape */
    exit(0);
    break;
  case 'L':
  case 'l':
    useLighting = !useLighting;
    useLighting ? glEnable(GL_LIGHTING) :
      glDisable(GL_LIGHTING);
    glutPostRedisplay();
    break;
  case 'F':
  case 'f':
    useFog = !useFog;
    useFog ? glEnable(GL_FOG) : glDisable(GL_FOG);
    glutPostRedisplay();
    break;
  case '1':
    glFogf(GL_FOG_MODE, GL_LINEAR);
    glutPostRedisplay();
    break;
  case '2':
    glFogf(GL_FOG_MODE, GL_EXP);
    glutPostRedisplay();
    break;
  case '3':
    glFogf(GL_FOG_MODE, GL_EXP2);
    glutPostRedisplay();
    break;
  case ' ':
    if (!moving) {
      idle();
      glutPostRedisplay();
    }
  }
}

void
display(void)
{
  GLfloat cubeXform[4][4];

  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

  glPushMatrix();
  glTranslatef(0.0, -1.5, 0.0);
  glRotatef(-90.0, 1, 0, 0);
  glScalef(2.0, 2.0, 2.0);

  drawCheck(6, 6, BLUE, YELLOW);  /* draw ground */
  glPopMatrix();

  glPushMatrix();
  glTranslatef(0.0, 0.0, -0.9);
  glScalef(2.0, 2.0, 2.0);

  drawCheck(6, 6, BLUE, YELLOW);  /* draw back */
  glPopMatrix();

  glPushMatrix();
  glTranslatef(0.0, 0.2, 0.0);
  glScalef(0.3, 0.3, 0.3);
  glRotatef((360.0 / (30 * 1)) * tick, 1, 0, 0);
  glRotatef((360.0 / (30 * 2)) * tick, 0, 1, 0);
  glRotatef((360.0 / (30 * 4)) * tick, 0, 0, 1);
  glScalef(1.0, 2.0, 1.0);
  glGetFloatv(GL_MODELVIEW_MATRIX, (GLfloat *) cubeXform);

  drawCube(RED);        /* draw cube */
  glPopMatrix();

  glDepthMask(GL_FALSE);
  if (useRGB) {
    glEnable(GL_BLEND);
  } else {
    glEnable(GL_POLYGON_STIPPLE);
  }
  if (useFog) {
    glDisable(GL_FOG);
  }
  glPushMatrix();
  myShadowMatrix(groundPlane, lightPos);
  glTranslatef(0.0, 0.0, 2.0);
  glMultMatrixf((const GLfloat *) cubeXform);

  drawCube(BLACK);      /* draw ground shadow */
  glPopMatrix();

  glPushMatrix();
  myShadowMatrix(backPlane, lightPos);
  glTranslatef(0.0, 0.0, 2.0);
  glMultMatrixf((const GLfloat *) cubeXform);

  drawCube(BLACK);      /* draw back shadow */
  glPopMatrix();

  glDepthMask(GL_TRUE);
  if (useRGB) {
    glDisable(GL_BLEND);
  } else {
    glDisable(GL_POLYGON_STIPPLE);
  }
  if (useFog) {
    glEnable(GL_FOG);
  }
  if (useDB) {
    glutSwapBuffers();
  } else {
    glFlush();
  }
}

void
fog_select(int fog)
{
  glFogf(GL_FOG_MODE, fog);
  glutPostRedisplay();
}

void
menu_select(int mode)
{
  switch (mode) {
  case 1:
    moving = 1;
    glutIdleFunc(idle);
    break;
  case 2:
    moving = 0;
    glutIdleFunc(NULL);
    break;
  case 3:
    useFog = !useFog;
    useFog ? glEnable(GL_FOG) : glDisable(GL_FOG);
    glutPostRedisplay();
    break;
  case 4:
    useLighting = !useLighting;
    useLighting ? glEnable(GL_LIGHTING) :
      glDisable(GL_LIGHTING);
    glutPostRedisplay();
    break;
  case 5:
    exit(0);
    break;
  }
}

void
visible(int state)
{
  if (state == GLUT_VISIBLE) {
    if (moving)
      glutIdleFunc(idle);
  } else {
    if (moving)
      glutIdleFunc(NULL);
  }
}

int
main(int argc, char **argv)
{
  int width = 640, height = 480;
  int i;
  char *name;
  int fog_menu;

  glutInitWindowSize(width, height);
  glutInit(&argc, argv);
  /* process commmand line args */
  for (i = 1; i < argc; ++i) {
    if (!strcmp("-c", argv[i])) {
      useRGB = !useRGB;
    } else if (!strcmp("-l", argv[i])) {
      useLighting = !useLighting;
    } else if (!strcmp("-f", argv[i])) {
      useFog = !useFog;
    } else if (!strcmp("-db", argv[i])) {
      useDB = !useDB;
    } else if (!strcmp("-logo", argv[i])) {
      useLogo = !useLogo;
    } else if (!strcmp("-quads", argv[i])) {
      useQuads = !useQuads;
    } else {
      usage();
    }
  }

  /* choose visual */
  if (useRGB) {
    if (useDB) {
      glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
      name = windowNameRGBDB;
    } else {
      glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);
      name = windowNameRGB;
    }
  } else {
    if (useDB) {
      glutInitDisplayMode(GLUT_DOUBLE | GLUT_INDEX | GLUT_DEPTH);
      name = windowNameIndexDB;
    } else {
      glutInitDisplayMode(GLUT_SINGLE | GLUT_INDEX | GLUT_DEPTH);
      name = windowNameIndex;
    }
  }

  glutCreateWindow(name);

  buildColormap();

  glutKeyboardFunc(keyboard);
  glutDisplayFunc(display);
  glutVisibilityFunc(visible);

  fog_menu = glutCreateMenu(fog_select);
  glutAddMenuEntry("Linear fog", GL_LINEAR);
  glutAddMenuEntry("Exp fog", GL_EXP);
  glutAddMenuEntry("Exp^2 fog", GL_EXP2);

  glutCreateMenu(menu_select);
  glutAddMenuEntry("Start motion", 1);
  glutAddMenuEntry("Stop motion", 2);
  glutAddMenuEntry("Toggle fog", 3);
  glutAddMenuEntry("Toggle lighting", 4);
  glutAddSubMenu("Fog type", fog_menu);
  glutAddMenuEntry("Quit", 5);
  glutAttachMenu(GLUT_RIGHT_BUTTON);

  /* setup context */
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  glFrustum(-1.0, 1.0, -1.0, 1.0, 1.0, 3.0);

  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
  glTranslatef(0.0, 0.0, -2.0);

  glEnable(GL_DEPTH_TEST);

  if (useLighting) {
    glEnable(GL_LIGHTING);
  }
  glEnable(GL_LIGHT0);
  glLightfv(GL_LIGHT0, GL_POSITION, lightPos);
  glLightfv(GL_LIGHT0, GL_AMBIENT, lightAmb);
  glLightfv(GL_LIGHT0, GL_DIFFUSE, lightDiff);
  glLightfv(GL_LIGHT0, GL_SPECULAR, lightSpec);
#if 0
  glLightfv(GL_LIGHT0, GL_SPOT_DIRECTION, lightDir);
  glLightf(GL_LIGHT0, GL_SPOT_EXPONENT, 80);
  glLightf(GL_LIGHT0, GL_SPOT_CUTOFF, 25);
#endif

  glEnable(GL_NORMALIZE);

  if (useFog) {
    glEnable(GL_FOG);
  }
  glFogfv(GL_FOG_COLOR, fogColor);
  glFogfv(GL_FOG_INDEX, fogIndex);
  glFogf(GL_FOG_MODE, GL_EXP);
  glFogf(GL_FOG_DENSITY, 0.5);
  glFogf(GL_FOG_START, 1.0);
  glFogf(GL_FOG_END, 3.0);

  glEnable(GL_CULL_FACE);
  glCullFace(GL_BACK);

  glShadeModel(GL_SMOOTH);

  glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
  if (useLogo) {
    glPolygonStipple((const GLubyte *) sgiPattern);
  } else {
    glPolygonStipple((const GLubyte *) shadowPattern);
  }

  glClearColor(0.0, 0.0, 0.0, 1);
  glClearIndex(0);
  glClearDepth(1);

  glutMainLoop();
  return 0;             /* ANSI C requires main to return int. */
}


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