8

614 Chapter 8: Modifiers
Wa rni ng: Don’tapplyanEditNormalsmodifierto
the low-res object used in
normal bump projection
(page 3–146)
. Normal bump projection relies on the
low-res object having standard nor mals, and altering
them causes normal bump maps to have unpredictable
results.
Typ es o f No rmals
Three types of normals are available with the Edit
Normals modifier:
• Unspecified: These are the normals that the
modifier derives from s moothing groups and
initially assigns to the modified mesh vertices.
Thesoftwarecalculatesthedirectionofan
unspecified normal based on the average facing
of all polygons to which it belongs that are in
its smoothing group.
Bydefault,eachvertexhasasmanynormals
asthenumberofuniquesmoothinggroups
used by surrounding polygons. For example,
each side of a box uses a different smoothing
groupbydefault,soeachvertex,atwhichthree
sides meet, has three different normals: one
perpendicular to each of the three sides. On the
other hand, a sphere uses a single smoothing
group, so each of its vertices has one normal,
perpendicular to the average facing of the
polygons that share it. By default, unspecified
normals are displayed as blue.
• Specif ied: These are normals that are intended
for use by particular corners of particular
faces, without regard to smoothing groups.
For instance, yo u might create a box, apply
Edit Normals, select a group of normals at a
particular vertex, and click Unify. Now those
three faces are told specific ally to use that
one unified normal, and they ignore their
smoothinggroupsatthatvertex.Butspecified
normals are not set to
explicit values; they
ignore smoothing groups, but they’re still based
on the face normals of the faces that use them.
Specified normals are displayed as c yan.
• Exp l i cit : These are normals that are set to
particular values. For instance, if you use the
Move or Rotate command to change a normal
from its default value, it has to be made explicit,
so it won’t be recomputed based on the face
normals. Explicit normals are green by default.
Note: Explicit normals are also considered to
be specified.
Note: Aselectednormalisalwaysred.Whennot
selected, its color indicates as type, as noted above.
Yo u c a n f i n d t h e
customizable color entr ies (page
3–843)
for these normal types in the Elements >
Geometry list. The three entry names are:
• Normals - Explicit
•Normals-Specified
•Normals-Unspecified
Usag e Ex a mples
Following are two instances in which a 3D artist
creating content for output to a game engine might
find practical use for the Edit Normals modifier:
• An artist is working on a knight with a chrome
shield. The chrome shield has a DirectX cube
map
shader (page 3–1104) on it so that the
artist can see the reflections in the viewport.
The artist would like to make the reflections
in the shield look "dented" by fig hts in battle.
TheartistappliestheEditNormalsmodifier
to the shield object. He then adjusts several
of the normals slightly, viewing the results in
real time, thanks to the pixel shader. He then
exports the character with a custom export tool
designed to handle normal information.
• A game artist is working on an object that will
explodeinthegame. Todothis,thegame
engine requires the object to be split into
multiple objects: the broken pieces that will
result from the explosion. When the object
is broken apart in 3ds Max (using Slice), the
normals are pointing in different directions;