In this lesson, we will start to get a good general understanding of that universe of ideas that goes under the name of "shading" or "surfacing." This is will be the first of two lessons on this subject.

We've touched on this subject in Lesson 5, though only briefly. You may wish to go back to that lesson (especially if you haven't already read it), before going forward here. The subject is so broad, and so important to good 3-D graphics and animation, that perhaps the greatest difficulty faced by the beginner is to grasp the basic lay of the landscape. The problem is compounded by different terminology used by different people and by different applications. Let's try to get this whole business organized so that, in the future, we can proceed with some firm ground beneath our feet.

To make sure we all speaking the same language, let's settle on the term SURFACING to describe the process of establishing all the apparent material properties of an object. People speak just as commonly of "shading" an object, or of "applying a material," but I have a distinct preference for the term "surfacing" because it more clearly encompasses all the things we can do to the surfaces of 3-D objects, many of which do not fit well into the idea of shading (which necessarily suggests only lighting and color). The full range of surfacing concepts ultimately blends back into modeling, because surfacing techniques can even be used to deform the geometry of an object. And such basic processes as making objects transparent or reflective do not fit intuitively into the concept of "shading." Surfacing is the most general and useful term, so let's use it here.

We don't usually have to think very precisely about the meaning of the "color" of an object in the real world. But when we enter the world of 3-D graphics, we must begin to think about this concept in much more precise ways. In the real world, the color of an object is the perception by our eye of light reflected from the surface of an object. This depends on both the color of the light before it reaches the object (for example, sunlight as opposed to a florescent bulb), and the chemical and physical nature of the object itself. This is oversimplified, but it will do for now.

Creating color in 3-D graphics is a peculiar mix of the physical principles from the real world and devices that simply work in practice and give good results. This is the root cause of so much confusion about surfacing techniques generally. The 3-D concepts follow our instincts up to a point, then suddenly diverge in directions that make more sense to the programmer than to the artist.

In rendering a 3-D scene, just as in the physical world, the apparent color of the object is result of the lighting and the object. Let's create a simple white sphere.

Hey! Is that really white? Well, my application tells me that I set my object's color to white. And the color of the spotlight looking down from behind is set to pure white. And even the ambient light (the general lighting that fills in the shadows) is set to white. But the object shades evenly from pure white to dark gray--which is exactly what a real white ball would do under the circumstances. If we change the spotlight to red, the white ball reflects red light, just as in the real world.

This is obviously different than having a ball with a red surface lit with a white light.

The basic concept of color is that of the interaction of a lighting of a given color and intensity with an object assigned a given color. The color of the assigned object for this purpose is called its DIFFUSE COLOR.