13.003 Computational Geometry and Visualization

OpenGL Lighting Functions

The necessary sequence of operations to perform shading with the OpenGL lighting model are:

• Associate a unit normal vector with each vertex in the geometric model
• Define the characteristics of the general lighting model
• Define and enable one or more light sources
  • At least eight light sources are available, GL_LIGHT0 through GL_LIGHT7
• Define the material properties
• Enable the lighting model

• Associate a unit normal vector with each vertex in the geometric model

    glNormal3{sifd}(nx, ny, nz);   /* specify normal at vertex */
    glVertex3{sifd}(x, y, z);      /* specify vertex */
    ...
  

• Define the lighting model

    float ambient[4]
  
    glLightModelfv(GL_LIGHT_MODEL_AMBIENT, ambient);  /* ambient RGB */
  

  Shading can be performed on both sides of the surface (ignoring the sign of the normal vector), or only on one side (the side with the positive normal vector).

    glLightModeli(GL_LIGHT_MODEL_TWO_SIDE, GL_TRUE);
    glLightModeli(GL_LIGHT_MODEL_TWO_SIDE, GL_FALSE);
  

• Define and enable light source(s)

    float ambient[4], diffuse[4], specular[4];
    float position[4];
    float kc, kl, kq;
  
    /* define the characteristics of light source 0 */
  
    glLightf(GL_CONSTANT,  GL_LIGHT0, Kc);  /* constant attenutation */
    glLightf(GL_LINEAR,    GL_LIGHT0, kl);  /* linear attenuation */
    glLightf(GL_QUADRATIC, GL_LIGHT0, kq);  /* quadratic attenuation */
  
    glLightfv(GL_AMBIENT,  GL_LIGHT0, ambient);   /* ambient RGB */
    glLightfv(GL_DIFFUSE,  GL_LIGHT0, diffuse);   /* diffuse RGB */
    glLightfv(GL_SPECULAR, GL_LIGHT0, specular);  /* specular RGB */
  
    glLightfv(GL_POSITION, GL_LIGHT0, position);
  
    /* define the characteristics of light source i */
    ...
  
    glEnable(GL_LIGHT0);           /* enable light source 0 */
    ...                            /* enable light source i */
  

  Light source i can be turned off with:

    glDisable(GL_LIGHTi);          /* disable light source i */
  

• Define the material properties

    float ambient[4], diffuse[4], emissive[4], specular[4];
    float shininess;
  
    glMaterialfv(face, GL_EMISSION, emission);    /* emissive RGB */
    glMaterialfv(face, GL_AMBIENT,  ambient);     /* ambient RGB */
    glMaterialfv(face, GL_DIFFUSE,  diffuse);     /* diffuse RGB */
    glMaterialfv(face, GL_SPECULAR, specular);    /* specular RGB */
    glMaterialf(face, GL_SHININESS, shininess);   /* specular exponent */
  

  where face can be either GL_FRONT, GL_BACK, or GL_FRONT_AND_BACK.

• Enable the lighting model

    glEnable(GL_LIGHTING);         /* enable the lighting model */
  

  The lighting model can be disabled with:

    glDisable(GL_LIGHTING);        /* disable the lighting model */