Cara Membuat Pengkabutan 3D dengan OpenGL

Syntax :
#include <GL/glut.h>
#include <math.h>
#include <stdlib.h>
#include <stdio.h>

static GLint fogMode;

/* inisialisasi kedalaman buffer, fog, sumber cahaya, sifat-sifat bahan dan model pencahayaan */
static void init(void)
{
       GLfloat position[] = { 0.5, 0.5, 3.0, 0.0 }; //pendeklarasisan posisi pencahayaan
       glEnable(GL_DEPTH_TEST); //pengaturan kedalaman buffer
       glLightfv(GL_LIGHT0, GL_POSITION, position);
       glEnable(GL_LIGHTING); //mengaktifkan pencahayaan
       glEnable(GL_LIGHT0);
       {
           GLfloat mat[3] = {0.1745, 0.01175, 0.01175};
           glMaterialfv (GL_FRONT, GL_AMBIENT, mat);
           mat[0] = 0.61424; mat[1] = 0.04136; mat[2] = 0.04136;
           glMaterialfv (GL_FRONT, GL_DIFFUSE, mat);
           mat[0] = 0.727811; mat[1] = 0.626959; mat[2] = 0.626959;
           glMaterialfv (GL_FRONT, GL_SPECULAR, mat);
           glMaterialf (GL_FRONT, GL_SHININESS, 0.6*128.0);
       }
      
       glEnable(GL_FOG);
       {
              GLfloat fogColor[4] = {0.5, 0.5, 0.5, 1.0};
              fogMode = GL_EXP;
              glFogi (GL_FOG_MODE, fogMode);
              glFogfv (GL_FOG_COLOR, fogColor);
              glFogf (GL_FOG_DENSITY, 0.35);
              glHint (GL_FOG_HINT, GL_DONT_CARE);
              glFogf (GL_FOG_START, 1.0);
              glFogf (GL_FOG_END, 5.0);
       }
       glClearColor(0.5, 0.5, 0.5, 1.0); /* memberi warna kabut */
}

static void renderSphere (GLfloat x, GLfloat y, GLfloat z)
{
       glPushMatrix();
       glTranslatef (x, y, z);
       glutSolidSphere(0.4, 16, 16);
       glPopMatrix();
}

/* display() untuk menampilkan gambar 5 sphere pada posisi z yang berbeda. */

void display(void)
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    renderSphere (-2., -0.5, -1.0);
    renderSphere (-1., -0.5, -2.0);
    renderSphere (0., -0.5, -3.0);
    renderSphere (1., -0.5, -4.0);
    renderSphere (2., -0.5, -5.0);
    glFlush();
}

void reshape(int w, int h)
{
    glViewport(0, 0, (GLsizei) w, (GLsizei) h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    if (w <= h)
        glOrtho (-2.5, 2.5, -2.5*(GLfloat)h/(GLfloat)w, 2.5*(GLfloat)h/(GLfloat)w, -10.0, 10.0);
    else
        glOrtho (-2.5*(GLfloat)w/(GLfloat)h,2.5*(GLfloat)w/(GLfloat)h, -2.5, 2.5, -10.0, 10.0);
        glMatrixMode(GL_MODELVIEW);
        glLoadIdentity ();
}

void keyboard(unsigned char key, int x, int y)
{
 switch (key) {
        case 'f':
        case 'F':
        if (fogMode == GL_EXP) {
           fogMode = GL_EXP2;
           printf ("Kabut dalam mode GL_EXP2\n");
        }
        else if (fogMode == GL_EXP2) {
            fogMode = GL_LINEAR;
            printf ("Kabut dalam mode GL_LINEAR\n");
        }
        else if (fogMode == GL_LINEAR) {
            fogMode = GL_EXP;
            printf ("Kabut dalam mode GL_EXP\n");
        }
        glFogi (GL_FOG_MODE, fogMode);
        glutPostRedisplay();
        break;
        case 27:
                exit(0);
        break;
              default:
        break;
        }
}

int main(int argc, char** argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB | GLUT_DEPTH);
    glutInitWindowSize(500, 500);
    glutCreateWindow("Program 1");
    init();
    glutReshapeFunc (reshape);
    glutKeyboardFunc (keyboard);
    glutDisplayFunc (display);
    glutMainLoop();
    return 0;
}

Run :