OpenGL Programming Guide

Chapter 7Blending, Antialiasing, and Fog

Fog

Using Fog

Using fog is easy. You enable it by passing GL_FOG to glEnable(), and you choose the color and the equation that controls the density with glFog*(). If you want, you can supply a value for GL_FOG_HINT with glHint(), as described on Table 7-2 . Example 7-6 draws five red teapots, each at a different distance from the viewpoint. Pressing the left mouse button selects among the three different fog equations, which are described in the next section.

Example 7-6 : Five Fogged Teapots in RGBA Mode: fog.c

#include <GL/gl.h>
#include <GL/glu.h>
#include <math.h>
#include "aux.h"

GLint fogMode;

void cycleFog (AUX_EVENTREC *event)
{
    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");
        glFogf (GL_FOG_START, 1.0);
        glFogf (GL_FOG_END, 5.0);
    }
    else if (fogMode == GL_LINEAR) {
        fogMode = GL_EXP;
        printf ("Fog mode is GL_EXP\n");
    }
    glFogi (GL_FOG_MODE, fogMode);
}

void myinit(void)
{
    GLfloat position[] = { 0.0, 3.0, 3.0, 0.0 };
    GLfloat local_view[] = { 0.0 };

    glEnable(GL_DEPTH_TEST);
    glDepthFunc(GL_LEQUAL);
    glLightfv(GL_LIGHT0, GL_POSITION, position);
    glLightModelfv(GL_LIGHT_MODEL_LOCAL_VIEWER, local_view);

    glFrontFace (GL_CW);
    glEnable(GL_LIGHTING);
    glEnable(GL_LIGHT0);
    glEnable(GL_AUTO_NORMAL);
    glEnable(GL_NORMALIZE);
    glEnable(GL_FOG);
    {
        GLfloat density;
        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);
        glClearColor(0.5, 0.5, 0.5, 1.0);
    }
}
void renderRedTeapot (GLfloat x, GLfloat y, GLfloat z)
{
    float mat[3];

    glPushMatrix();
    glTranslatef (x, y, z);
    mat[0] = 0.1745; mat[1] = 0.01175; mat[2] = 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);
    auxSolidTeapot(1.0);
    glPopMatrix();
}

void display(void)
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    renderRedTeapot (-4.0, -0.5, -1.0);
    renderRedTeapot (-2.0, -0.5, -2.0);
    renderRedTeapot (0.0, -0.5, -3.0);
    renderRedTeapot (2.0, -0.5, -4.0);
    renderRedTeapot (4.0, -0.5, -5.0);
    glFlush();
}

void myReshape(GLsizei w, GLsizei h)
{
    glViewport(0, 0, w, h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    if (w <= (h*3))
        glOrtho (-6.0, 6.0, -2.0*((GLfloat) h*3)/(GLfloat) w, 
         2.0*((GLfloat) h*3)/(GLfloat) w, 0.0, 10.0);
    else
        glOrtho (-6.0*(GLfloat) w/((GLfloat) h*3), 
         6.0*(GLfloat) w/((GLfloat) h*3), -2.0, 2.0, 0.0, 10.0);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity ();
}


int main(int argc, char** argv)
{
    auxInitDisplayMode (AUX_SINGLE | AUX_RGBA | AUX_DEPTH);
    auxInitPosition (0, 0, 450, 150);
    auxInitWindow (argv[0]);
    auxMouseFunc (AUX_LEFTBUTTON, AUX_MOUSEDOWN, cycleFog);
    myinit();
    auxReshapeFunc (myReshape);
    auxMainLoop(display);
}

OpenGL Programming Guide