OpenGL Programming Guide

Chapter 6Lighting

A Simple Example: Rendering a Lit Sphere

These are the steps required to add lighting to your scene:

1. Define normal vectors for each vertex of all the objects. These normals determine the orientation of the object relative to the light sources.
   
   

2. Create, select, and position one or more light sources.
   
   

3. Create and select a lighting model, which defines the level of global ambient light and the effective location of the viewpoint (for the purposes of lighting calculations).
   
   

4. Define material properties for the objects in the scene.

Example 6-1 accomplishes these tasks. It displays a sphere illuminated by a single light source, as shown earlier in Figure 6-1 .

Example 6-1 : Drawing a Lit Sphere:

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

void myinit(void)
{
    GLfloat mat_specular[] = { 1.0, 1.0, 1.0, 1.0 };
    GLfloat mat_shininess[] = { 50.0 };
    GLfloat light_position[] = { 1.0, 1.0, 1.0, 0.0 };

    glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);
    glMaterialfv(GL_FRONT, GL_SHININESS, mat_shininess);
    glLightfv(GL_LIGHT0, GL_POSITION, light_position);

    glEnable(GL_LIGHTING);
    glEnable(GL_LIGHT0);
    glDepthFunc(GL_LEQUAL);
    glEnable(GL_DEPTH_TEST);
}

void display(void)
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    auxSolidSphere(1.0);
    glFlush();
}

void myReshape(GLsizei w, GLsizei h)
{
    glViewport(0, 0, w, h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    if (w <= h) 
        glOrtho (-1.5, 1.5, -1.5*(GLfloat)h/(GLfloat)w, 
            1.5*(GLfloat)h/(GLfloat)w, -10.0, 10.0);
    else 
        glOrtho (-1.5*(GLfloat)w/(GLfloat)h, 
            1.5*(GLfloat)w/(GLfloat)h, -1.5, 1.5, -10.0, 10.0);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}


int main(int argc, char** argv)
{
    auxInitDisplayMode (AUX_SINGLE | AUX_RGBA | AUX_DEPTH);
    auxInitPosition (0, 0, 500, 500);
    auxInitWindow (argv[0]);
    myinit();
    auxReshapeFunc (myReshape);
    auxMainLoop(display);
}

The lighting-related calls are in the myinit() command; they're discussed briefly in the following paragraphs and in more detail later in the chapter. One thing to note about Example 6-1 is that it uses RGBA color mode, not color-index mode. OpenGL's lighting calculation is different for the two modes, and in fact the lighting capabilities are more limited in color-index mode. Thus, RGBA is the preferred mode when doing lighting, and all the examples in this chapter use it. See "Lighting in Color-Index Mode" for more information about lighting in color-index mode.

Define Normal Vectors for Each Vertex of All the Objects
Create, Position, and Enable One or More Light Sources
Select a Lighting Model
Define Material Properties for the Objects in the Scene
Some Important Notes

OpenGL Programming Guide