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Show to provide realistic lighting of th database. Shading mod Is combin am i nt, diffuse, and specular reflections to create realistically shaded objects. Most shading models calculate the intensity of a point on the surface of an object as a fun tion of three vectors: the light source, the eyepoint, and the surface normal of th object. Some shading models also provide effects such as reflection, refraction and shadows. To allow textured objects, the image synthesis program must also handle the texture mapping operation. 2.1.1 Ray Tracing Ray tracing is an image synthesis technique. The basic algorithm positions a viewing screen within the database, then fires rays from that screen into the database. Intersections between the rays and objects are calculated, with the closest intersection being stored in a ray tree. After the closest intersection is found, reflecting and refracting rays are started in a recursive process that continues until each ray finally encounters a light source, or encounters nothing. A shading model is applied to the ray tree to calculate the illumination at each point on the viewing screen. The final product is a picture of the database. The ray tracing algorithm is shown in Figure 1. 2.1.2 Representation of Objects This thesis will explore perturbing the surfaces of polygonal and quadric objects. A quadric object is defined mathematically by position coordinate ( trans.x, |
