Surface Decoration: Motivation

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Motivation:

It would be too tedious to describe all the rich details that we observe in natural scenes with individual polygons and polyhedrons!

Texture mapping:

A simple way to make a surface more interesting is by texture mapping. The texture map provides a look-up table for the local color on a piece of surface.
Two more scalar values need to be stored at each vertex (s,t).
Rendering textures is easy: Bilinear interpolation of the texture coordinates s,t.
If the geometric coordinates and the texture coordinates of a facet are not matched, serious distortion can result.
Modeling is more difficult: How to assign texture coordinates to avoid pattern discontinuities on objects of high genus that loop back onto themselves?

Bump mapping:

Jiggle the vertex normals to produce changes in shading that simulate the existence of height variations on the surface.
However, at the silhouette edges one can still see clearly that the surface is primarily polyhedral.

Displacement mapping:

In this technique a varying incremental height-offset is specified over the surface,and a more complictaed computation is applied to determine how this changes the intersection point with a given ray and how it affects the surface normal at the intersection point.

Environment mapping:

This is a cheap way to simulate highly reflective objects in complex environments.
Rather than actually tracing rays from the shiny surface into the environment to see what gets hit, we use s single global surrounding picture of the environment which simply gets accessed with the direction of the reflected ray. Any local intersections with real objects in the scene are ignored.
Example, the surroundings of a bar in Palo Alto reflected in a shiny sculpture.

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