9.5.2

770 • CHAPTER 17
OBJECT MANAGER • 771
To see the normals, select their polygons. For example, create a sphere and
choose Functions > Make Editable (this will convert the sphere to polygons).
Select the Polygon tool from the left toolbar and select some polygons using
one of the selection tools (or choose Edit > Select All). The normals appear
as thin, yellow lines perpendicular to the surface. To align normals, choose
Functions > Align Normals.
If a Phong tag is activated, the normals will be interpolated. There will be a soft transition between
one normal and the next (provided that the surfaces are connected). If a Phong tag is not applied,
there will be no interpolation.
Figure 1. Figure 1a: light
course.
Figure 2. Figure 2a: light
course.
Figure 1 shows three connected surfaces. The middle surface is not aligned to the other surfaces (you
can tell by the direction of the normals). Figure 1a illustrates how the normals are interpolated for
smoothing. The light bar shows the hard transition caused by the non-alignment.
Figure 2 shows the same three surfaces, but this time they are aligned. Notice how the interpolation
(Figure 2a) is much smoother this time. The light bar is smoother as a result.
These pictures illustrate why it is important for surfaces to be aligned. The convention is that the
normals should point outwards from the object. For example, if you have an apple, the normals should
point outwards into the world, not inwards towards the core.
The normal direction plays an important part in decal mapping, such as when you put labels onto
bottles. All primitive objects are created with aligned normals (you do not need to edit their normals
— they will be correct).
Use Edge Breaks
The broken edges in red and the rendered result.