Real-Time Rendering, Third Edition, 3rd Edition

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Chapter 6

Texturing

“All it takes is for the rendered image to look right.”

—Jim Blinn

A surface’s texture is its look and feel—just think of the texture of an oil

painting. In computer graphics, texturing is a process that takes a surface

and modifies its appearance at each location using some image, function,

or other data source. As an example, instead of precisely representing the

geometry of a brick wall, a color image of a brick wall is applied to a single

polygon. When the polygon is viewed, the color image appears where the

polygon is located. Unless the viewer gets close to the wall, the lack of

geometric detail (e.g., the fact that the image of bricks and mortar is on a

smooth surface) will not be noticeable. Color image texturing also provides

a way to use photographic images and animations on surfaces.

However, some textured brick walls can be unconvincing for reasons

other than lack of geometry. For example, if the mortar is supposed to be

glossy, whereas the bricks are matte, the viewer will notice that the gloss is

the same for both materials. To produce a more convincing experience, a

second image texture can be applied to the surface. Instead of changing the

surface’s color, this texture changes the wall’s gloss, depending on location

on the surface. Now the bricks have a color from the color image texture

and a gloss value from this new texture.

Once the gloss texture has been applied, however, the viewer may notice

that now all the bricks are glossy and the mortar is not, but each brick

face appears to be flat. This does not look right, as bricks normally have

some irregularity to their surfaces. By applying bump mapping,thesurface

normals of the bricks may be varied so that when they are rendered, they

do not appear to be perfectly smooth. This sort of texture wobbles the

direction of the polygon’s original surface normal for purposes of computing

lighting.

From a shallow viewing angle, this illusion of bumpiness can break

down. The bricks should stick out above the mortar, obscuring it from

view. Even from a straight-on view, the bricks should cast shadows onto

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148 6. Texturing

Figure 6.1. Texturing. Color, bump, and parallax occlusion texture mapping methods

are used to add complexity and realism to a scene. (Image from “Toyshop” demo

courtesy of Natalya Tatarchuk, ATI Research, Inc.)

the mortar. Parallax and relief mapping use a texture to appear to deform

a flat surface when rendering it. Displacement mapping actually displaces

the surface, creating triangles between the texels. Figure 6.1 shows an

example.

These are examples of the types of problems that can be solved with

textures, using more and more elaborate algorithms. In this chapter, tex-

turing techniques are covered in detail. First, a general framework of the

texturing process is presented. Next, we focus on using images to texture

surfaces, since this is the most popular form of texturing used in real-time

work. Procedural textures are briefly discussed, and then some common

methods of getting textures to affect the surface are explained.

6.1 The Texturing Pipeline

Texturing, at its simplest, is a technique for efficiently modeling the sur-

face’s properties. One way to approach texturing is to think about what

happens for a single shaded pixel. As seen in the previous chapter, the

color is computed by taking into account the lighting and the material, as

well as the viewer’s position. If present, transparency also affects the sam-