Chapter 19: Controlling Shading

Understanding Normals

Figure 19.1


A box with its normals indicated with arrows.

Shading Based on Normal Directions

Figure 19.2


Your headlight, like a miner's headlight.

Figure 19.3


A face shaded based on its orientation toward or away from the headlight.

Figure 19.4


A shaded face with its normal, a light source, a and a light line.

Figure 19.5


Shading variations based on a f ace's orientation toward a light source.

Figure 19.6


Shading variations based on the face's orientation toward a light source.

Determining Normal Directions

Figure 19.7


A triangle described by an indexed face set.

Figure 19.8


The right-hand rule for normals, the right-hand rules from the back of the face, and applying the right-hand rule to a more complex shape.

Computing Normals

Figure 19.9


Two vectors computed for the triangle.

Figure 19.10


The V and W vectors computed for the triangle.

Figure 19.11


The normal for the triangle.

Understanding Smooth Shading

Figure 19.12


Four rectangles composing a half column's facets in outline form viewed from the front, shaded and viewed from the front, and in outline form viewed from above.

Figure 19.13


Using more facets to create smoother shading: four facets, five facets, six facets, and seven facets.

Figure 19.14


The shaded half column using normals that create a smooth-shading effect.

Smooth Shading and Normals

Figure 19.15


The top view of a half column built using four faces, and the top view of a perfectly rounded half column.

Figure 19.16


The top view of a half column with normals for each face in a faceted half column and pointing outward from the center for a perfectly rounded half column.

Figure 19.17


Comparing facet normals with the perfectly rounded half column's normals. Top view of normals pointing out from each coordinate of a face.

Figure 19.18


Comparing normals of facet coordinates and the perfectly rounded half column's normals, and corrected normals pointing out from each face's coordinates.

Figure 19.19


Comparing half-column shading : faceted, smoothly shaded and faceted, and smoothly rounded.

Computing Smooth-Shading Normals

Figure 19.20


The normals for a sine-wave shape.

Crease Angles

Understanding Normal Binding

Face-Set Normals

Elevation-Grid Normals

Understanding Normal Animation

The Normal Node Syntax

The NormalInterpolator Node Syntax

The IndexedFaceSet Node Sytnax

The ElevationGrid Node Syntax

Experimenting with Normals

Using Normals

Figure 19.21


A square face and four normals.

Figure 19.22


A square face with two normals pointing along the positive Z axis and two normals pointing along the positive X axis.

Smoothly Shading a Half Column

Figure 19.23


A faceted half column.

Figure 19.24a


A smooth-shaded half column using a crease angle. Compare with Figure 19.24b.

Figure 19.24b


Two half columns with a visible seam caused by inaccuracies in the crease-angle method of computing normals. Compare with Figure 19.24a.

Figure 19.25a


A smooth-shaded half column using custom normals. Compare with Figure 19.25b.

Figure 19.25b


Two half columns without a visible seam. Compare with Figure 19.25a.

Smoothly Shading an Elevation Grid

Figure 19.26


An elevation grid using a special shading effect.

Animating Normals

Figure 19.27


A square face and animated normals.

Summary