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168 Chapter 5: Creating Geometry
Smoothing is controlled by smoothing groups,
which are numbered groups ranging from 1 to 32.
Each face is assigned to one or more smoothing
groups. When a scene is rendered, the renderer
checks each adjacent pair of faces to see if they
share a smoothing group, and renders the object
as follows:
• If faces have no smoothing groups in common,
thefacesarerenderedwithasharpedge
between them.
• If faces have at least one smoothing group
incommon,theedgebetweenthefacesis
“smoothed”, meaning it is shaded in such a
way that the area where the faces meet appears
smooth.
Becauseeachfacehasthreeedges,onlythree
smoothing groups can b e in effect for any face.
Extra smoothing groups assigned to a face are
ignored.
Do one of the following to view or change
smoothing group assignments:
• Turn on the Smooth check box on the
Parameters rollout of a parametric object to set
default smoothing for the object.
• TurnontheAutoSmoothcheckboxonthe
Rendering rollout of a spline shape to turn on
smoothing.
•ApplyaSmooth modifier (page 1 –828).IfaFace
sub-object selection i s active, Smooth applies
to the selected faces. If no faces are selected,
Smooth applies to the entire object.
•ApplyanEdit Mesh modifier (page 1–634),
enable Face (or Polygon or Element) sub-object
mode,thenusethefeaturesontheSurface
Properties rollout.
•Converttheobjecttoaneditable mesh (page
1–996),enableFace(orPolygonorElement)
sub-object mode, then use the features on t he
Surface Properties rollout.
Viewing S moothing G roups
The easiest way to view smoothing is to look at an
object in a shaded viewport. In this case, you are
not viewing the smoothing groups themselves but
rather their effects on the shaded surface.
You can see the smo othing group numbers for
selected faces of an editable mesh object or the Edit
Mesh modifier by looking at the Smo othing Group
buttonsontheSurfacePropertiesrollout,orof
an editable poly object on the Polygon Properties
rollout.
SmoothingGroupbuttonsappearasfollows:
• Group numbers not used by any face in the
selection, appear normal.
•Groupnumbersusedbyallfacesinthe
selection, appear selected.
•Groupnumbersusedbysome,butnotall,faces
in the select ion, appear blank.
Automaticall y Smoothing a n Object
Click Auto Smooth to assign smoothing
automatically. You set a Threshold ang le to
determine whether to smooth adjacent faces.
• If the angle between face normals is less than or
equal to the threshold, the faces are assigned to
a common smoothing group.
• If the angle between face normals is greater
than the threshold, the faces are assig ned to
separate g roups.
Auto Smooth is found on the Surface Properties
rollout and on the Smooth modifier.
Ma nua lly Appl yi ng S moothing G r oups
You manually assign smoothing groups to a
selection of faces by clicking Smoothing Group
buttonsontheSurfacePropertiesrolloutorthe
Smooth modifier. The smoothing group of each
button you click is assigned to the selection.