OpenGL Programming Guide

Chapter 6Lighting

Defining Material Properties

Specular Reflection

Specular reflection from an object produces highlights. Unlike ambient and diffuse reflection, the amount of specular reflection seen by a viewer does depend on the location of the viewpoint - it's brightest along the direct angle of reflection. To see this, imagine looking at a metallic ball outdoors in the sunlight. As you move your head, the highlight created by the sunlight moves with you to some extent. However, if you move your head too much, you lose the highlight entirely.

OpenGL allows you to set the RGBA color of a specular highlight (with GL_SPECULAR) and to control the size and brightness of the highlight (with GL_SHININESS). You can assign a number in the range of [0.0, 128.0] to GL_SHININESS - the higher the value, the smaller and brighter (more focused) the highlight. See "The Mathematics of Lighting" for the details of how specular highlights are calculated.

In Figure J-21 , the spheres in the first column have no specular reflection. In the second column, GL_SPECULAR and GL_SHININESS are assigned values as follows:

GLfloat mat_specular[] = { 1.0, 1.0, 1.0, 1.0 };
GLfloat low_shininess[] = { 5.0 };
glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);
glMaterialfv(GL_FRONT, GL_SHININESS, low_shininess);

In the third column, the GL_SHININESS parameter is increased to 100.0.

OpenGL Programming Guide