Frame after moving the object instead of the camera, allowing the surface to vary completely from cool to warm. This will be discussed further in Chapter 5 . This would mean moving the object, not the viewpoint. For example, two objects in a scene may be lit differently to draw attention to different attributes of each object. If this was accomplished by adding two lights to the environment, the multiple highlights would be confusing.
Most material properties are semiconstant as the view direction or lighting changes.
However the metal shading presented in Section 4.2.3 is the replication of the anisotropic reflection due to the surface of the object and the reflection of the environment. When a real metal part is rotated in one's hand, the banding does not stick to the object, but remains constant since the environment is not changing. However, in an non-photorealistic interactive environment it may be too jarring to have the metal shading changing abruptly. Using a metal texture would be more appropriate and a metal texture in an interactive environment would still convey the material property. Another notion is to allow the relative size of the object to control the motion of the viewer, the object, and the light source in an interactive 3D illustration.