Web hosting unlimited bandwidth - Page 316 OpenGL Super Bible! // Nice light
Page 316 OpenGL Super Bible! // Nice light blue background glClearColor(0.0f, 0.0f, 05.f,1.0f); } Using a Light Source Manipulating the ambient light has its uses, but for most applications attempting to model the real world, one or more specific sources of light must be specified. In addition to their intensities and colors, these sources will have a location and a direction. The placement of these lights can dramatically affect the appearance of your scene. OpenGL supports up to eight independent light sources located anywhere in your scene or out of the viewing volume. You can locate a light source an infinite distance away and make its light rays parallel, or make it a nearby light source radiating outward. You can also specify a spotlight with a specific cone of light radiating from it, as well as manipulate its characteristics. Which Way Is Up? When you specify a light source, you tell OpenGL where it is and in which direction it s shining. Often the light source will be shining in all directions, or it may be directional. Either way, for any object you draw, the rays of light from any source (other than a pure ambient source) will strike the surface of the polygons that make up the object at an angle. Of course, in the case of a directional light, the surface of all polygons may not necessarily be illuminated. To calculate the shading effects across the surface of the polygons, OpenGL must be able to calculate this angle. In Figure 9-9, a polygon (a square) is being struck by a ray of light from some source. The ray makes an angle (A) with the plane as it strikes the surface. The light is then reflected at an angle (B) toward the viewer (or you wouldn t see it). These angles are used in conjunction with the lighting and material properties we have discussed thus far to calculate the apparent color of that location. It happens by design that the locations used by OpenGL are the vertices of the polygon. By calculating the apparent colors for each vertex and then doing smooth shading between them (explained in Chapter 
, the illusion of lighting is created. Magic!
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