fog.c

// from the OpenGL Redbook
// generates a steadily increasing fog in a scene

#include <stdio.h>
#include <GL/glut.h>

static GLint fogMode;

static void init(void){
  GLfloat position[] = {0.5, 0.5, 3.0, 0.0};
  
  glEnable(GL_DEPTH_TEST);
  
  glLightfv(GL_LIGHT0, GL_POSITION, position);
  glEnable(GL_LIGHTING);
  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);
  }
  
  // fog color
  glClearColor(0.5, 0.5, 0.5, 1.0);
}

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

// display draws 5 spheres at different z positions
void display(void){
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
  renderSphere(-2.0, -0.5, -1.0);
  renderSphere(-1.0, -0.5, -2.0);
  renderSphere(0.0, -0.5, -3.0);
  renderSphere(1.0, -0.5, -4.0);
  renderSphere(2.0, -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("Fog mode is GL_EXP2\n");
      
      }else if(fogMode == GL_EXP2){
        fogMode = GL_LINEAR;
        printf("Fog mode is GL_LINEAR\n");
      
      }else if(fogMode == GL_LINEAR){
        fogMode = GL_EXP;
        printf("Fog mode is 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(argv[0]);
  init();
  glutReshapeFunc(reshape);
  glutKeyboardFunc(keyboard);
  glutDisplayFunc(display);
  glutMainLoop();
  return 0;
}