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Edit Nor mals Modifier 635
Wa rning: Don’t apply an Edit Normals modifier to the
low-res object used in normal bump projection (page
3–150). Normal bump projection relies o n the low-res
object having standard normals, and altering them
causes normal bump maps to have unpredictable
results.
Typ e s of Normals
Three types of normals are available with the Edit
Normals modifier:
• Unspecified: These are the normals that the
modifier derives from smoothing 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.
By default, each vertex has as m any normals as
thenumberofuniquesmoothinggroupsused
by surrounding polygons. For example, each
sideofaboxusesadifferentsmoothinggroup
by default, so each vertex at which three sides
meet (ty pical ly a corner) has three different
normals: one perpendicular to each of the
three s ides. On the other hand, a sphere uses a
single smoothing group, s o each of its vert ices
has one normal, p er pendicular to the average
facing of the polygons that share it. By default,
unspecified normals are displayed as blue.
• Specified: These are normals that are intended
for use by particular corners of particular
faces, without regard to smoothing groups.
For instance, you might create a box, apply
Edit Normals, selec t a group of normals at a
particular vertex, and click Unify. Now those
three faces are told specifically 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 cyan.
• Expl 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 ty pe, as noted above.
Yo u c a n f i n d t h e customizable color entries (page
3–799) for these normal types in the Elements >
Geometry list. The three entry names are:
• Normals - Explicit
•Normals-Specified
•Normals-Unspecified
Usag e E x ampl es
Following are two instances in which a 3D artist
creating content for output to a game engine might
find practica l 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 3–1010) on it so that the
artist can see the reflections in the viewport.
The artist would like to make the reflections
in the shield lo ok "dented" by fights in battle.
TheartistappliestheEditNormalsmodifier
to the shield object. He then adjusts several
of the norm a ls slightly, v iewing the results in
real tim e, 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 wil l
result from the explosion. When the object
is broken apart in 3ds Max (using Slice), the
normals are pointing i n different directions;