What's it all about?A somewhat abstract rendering may sometimes be desirable. However, even the fairly simple notion of simulating traditional 'abstract' modeling materials such as poster-board or cardboard requires more visual variation, or texture, than simple flat cosine shading produces. Including items in a scene like a brick wall, a tatami mat, or a famous piece of artwork is even less possible without special techniques.
These things are accomplished through a technology called texture mapping. This extends far beyond the simple application, which is analagous to wrapping patterned 2D paper around the object. The term texture maps now covers a variety of simulated details:
- changes in surface coloration, such as bricks, tiles, and wallpaper
- small changes in surface geometry, such as stucco, traction grids on steel plates, grout lines in tile
- "stand-up cutouts" of people, trees, etc.
- effects that might otherwise require geometry editing, like open arches in a distant arcade
The Big Picture
One way to understand texture maps is to see them all as variations on a theme. The primary theme is the basic cosine shading term
In terms of a black & white image, this equation says, "The color of the surface (Is) depends on the amount of incident light (Ii), the color of the surface (ks), and the angle of incidence (cos θ)". Each major type of texture map is approached by making one or more terms in this equation into a function of location on the surface of the object. In other words, allow them to vary across the surface.
Last updated: April, 2014