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>Blender Documentation Volume I - User Guide: Last modified April 29 2004 S68</TH
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><H1
CLASS="section"
><A
NAME="mesh_modeling_subsurf"
></A
>Catmull-Clark Subdivision Surfaces</H1
><P
> With any regular Mesh as a starting point, Blender can calculate
a smooth subdivision on the
fly, while modelling or while rendering, using Catmull-Clark Subdivision
Surfaces or, in short <I
CLASS="emphasis"
>SubSurf</I
>. SubSurf
is a mathematical algorithm to compute a "smooth" subdivision of a mesh.
This allows high resolution
Mesh modelling without the need to save and maintain huge amounts of
data. This also allows for a smooth 'organic' look to the models.
</P
><P
> Actually a SubSurfed Mesh and a NURBS surface have many points in common
inasmuch as
both rely on a "coarse" low-poly "mesh" to define a smooth "high
definition"
surface. But there are also notable differences:
</P
><P
></P
><UL
><LI
><P
>NURBS allow for finer control on the surface, since you can set
"weights" independently on each control point of the control mesh.
On a SubSurfed mesh you cannot act on weights.</P
></LI
><LI
><P
>SubSurfs have a more flexible modelling approach. Since a SubSurf is
a mathematical operation occurring on a mesh, you can use all the
modelling techniques described in this chapter on the mesh. There are more techniques,
which are far more flexible,
than those available for NURBS control polygons.</P
></LI
></UL
><P
> SubSurf is a Mesh option, activated in the
Editing Context <TT
CLASS="literal"
>Mesh</TT
> Panel (<B
CLASS="keycap"
>F9</B
> -
<A
HREF="x3169.html#BSG.EDT.F.S68.1101"
>Figure 57</A
>).
The Num Buttons immediately below it define, on the left, the resolution
(or level)
of subdivision for 3D visualization purposes; the one on the right, the
resolution for rendering purposes. You can also use <B
CLASS="keycap"
>SHIFT-O</B
> if you are in
ObjectMode. This switches SubSurf On/Off. The SubSurf level can also be
controlled via <B
CLASS="keycap"
>CTRL-1</B
> to <B
CLASS="keycap"
>CTRL-4</B
>,
but this only affects the visualization sub-division level.
</P
><P
> Since SubSurf computations are performed both real-time, while you model,
and at render time, and they are CPU intensive, it is usually
good practice to keep the SubSurf level low (but non-zero) while
modelling; higher while rendering.
</P
><DIV
CLASS="figure"
><A
NAME="BSG.EDT.F.S68.1101"
></A
><DIV
CLASS="mediaobject"
><P
><IMG
SRC="PartM/mesh_modeling/gfx/SubSurf04.png"></P
></DIV
><P
><B
>Figure 57. SubSurf buttons </B
></P
></DIV
><P
>
From version 2.3 Blender has a new SubSurfed-related button:
<TT
CLASS="literal"
>Optimal</TT
>. This changes the way SubSurf meshes are drawn and
can be of great help in modelling. <A
HREF="x3169.html#BSG.EDT.F.S68.1102"
>Figure 58</A
>
shows a series of pictures showing various different combinations on Suzanne's Mesh.
</P
><DIV
CLASS="figure"
><A
NAME="BSG.EDT.F.S68.1102"
></A
><DIV
CLASS="mediaobject"
><P
><IMG
SRC="PartM/mesh_modeling/gfx/SubSurf01.png"></P
></DIV
><P
><B
>Figure 58. SubSurfed Suzanne.</B
></P
></DIV
><P
> <A
HREF="x3169.html#BSG.EDT.F.S68.1104"
>Figure 59</A
> shows a 0,1,2,3 level of SubSurf on
a single square face or
on a single triangular face. Such a subdivision is performed, on a
generic mesh, for <I
CLASS="emphasis"
>each</I
>
square or rectangular face.
</P
><P
> It is evident how each single quadrilateral face produces
<I
CLASS="emphasis"
>4^n</I
> faces in the SubSurfed mesh.
<I
CLASS="emphasis"
>n</I
> is the SubSurf level, or resolution, while each
triangular face
produces <I
CLASS="emphasis"
>3*4^(n-1)</I
> new faces (<A
HREF="x3169.html#BSG.EDT.F.S68.1104"
>Figure 59</A
>). This dramatic increase
of face (and vertex) number results in a slow-down of all editing, and
rendering,
actions and calls for lower SubSurf level in the editing process than in
the rendering one.
</P
><DIV
CLASS="figure"
><A
NAME="BSG.EDT.F.S68.1104"
></A
><DIV
CLASS="mediaobject"
><P
><IMG
SRC="PartM/mesh_modeling/gfx/SubSurf04b.png"></P
></DIV
><P
><B
>Figure 59. SubSurf of simple square and Rectangular faces.</B
></P
></DIV
><P
> Blender's subdivision system is based on the Catmull-Clarke algorithm.
This produces nice smooth SubSurf meshes but any 'SubSurfed' face,
that is, any small face created by the algorithm from a single
face of the original mesh, shares the normal orientation of that
original face.
</P
><P
> This is not an issue for the shape itself, as
<A
HREF="x3169.html#BSG.EDT.F.S68.1105"
>Figure 60</A
> shows, but it is an issue
in the rendering phase and in solid mode, where abrupt normal changes
can produce ugly black lines (<A
HREF="x3169.html#BSG.EDT.F.S68.1106"
>Figure 61</A
>).
</P
><DIV
CLASS="figure"
><A
NAME="BSG.EDT.F.S68.1105"
></A
><DIV
CLASS="mediaobject"
><P
><IMG
SRC="PartM/mesh_modeling/gfx/SubSurf05a.png"></P
></DIV
><P
><B
>Figure 60. Side view of subsurfed meshes. With random normals (top) and with
coherent normals (bottom)</B
></P
></DIV
><P
> Use the <B
CLASS="keycap"
>CTRL+N</B
> command in EditMode, with all vertices
selected, to make Blender recalculate the normals.
</P
><DIV
CLASS="figure"
><A
NAME="BSG.EDT.F.S68.1106"
></A
><DIV
CLASS="mediaobject"
><P
><IMG
SRC="PartM/mesh_modeling/gfx/SubSurf05b.png"></P
></DIV
><P
><B
>Figure 61. Solid view of SubSurfed meshes with inconsistent normals (top) and
consistent normals (bottom).</B
></P
></DIV
><P
> In these images the face normals are drawn cyan.
You can enable drawing normals in the
EditButtons (<B
CLASS="keycap"
>F9</B
>) menu.
</P
><P
> Note that Blender cannot recalculate normals correcty if the mesh is
not "Manifold". A "Non-Manifold" mesh is a mesh for which an 'out' cannot
unequivocally be computed. Basically, from the Blender point of view,
it is a mesh where there are edges belonging to <I
CLASS="emphasis"
>more</I
>
than two faces.
</P
><P
> <A
HREF="x3169.html#BSG.EDT.F.S68.1107"
>Figure 62</A
> shows a very simple example of a
"Non-Manifold" mesh. In general a "Non-Manifold" mesh occurs when
you have internal faces and the like.
</P
><DIV
CLASS="figure"
><A
NAME="BSG.EDT.F.S68.1107"
></A
><DIV
CLASS="mediaobject"
><P
><IMG
SRC="PartM/mesh_modeling/gfx/SubSurf06.png"></P
></DIV
><P
><B
>Figure 62. A "Non-Manifold" mesh</B
></P
></DIV
><P
> A "Non-Manifold" mesh is not a problem for conventional meshes,
but can give rise to ugly artifacts in SubSurfed meshes. Also, it
does not allow decimation,
so it is better to avoid them as much as possible.
</P
><P
> Use these two hints to tell whether a mesh is "Non Manifold":
</P
><P
></P
><UL
><LI
><P
> The Recalculation of normals leaves black lines somewhere
</P
></LI
><LI
><P
> The "Decimator" tool in the <TT
CLASS="literal"
>Mesh</TT
> Panel refuses to work
stating that the mesh is "No Manifold"
</P
></LI
></UL
><P
> The SubSurf tool allows you to create very good "organic" models,
but remember that a regular Mesh with square faces, rather than
triangular ones, gives the best results.
</P
><P
> <A
HREF="x3169.html#BSG.EDT.F.S68.1108"
>Figure 63</A
> and
<A
HREF="x3169.html#BSG.EDT.F.S68.1109"
>Figure 64</A
> show an example of what
can be done with Blender SubSurfs.
</P
><DIV
CLASS="figure"
><A
NAME="BSG.EDT.F.S68.1108"
></A
><DIV
CLASS="mediaobject"
><P
><IMG
SRC="PartM/mesh_modeling/gfx/SubSurf07.png"></P
></DIV
><P
><B
>Figure 63. A Gargoyle base mesh (left) and pertinent level 2 SubSurfed Mesh
(right).</B
></P
></DIV
><DIV
CLASS="figure"
><A
NAME="BSG.EDT.F.S68.1109"
></A
><DIV
CLASS="mediaobject"
><P
><IMG
SRC="PartM/mesh_modeling/gfx/SubSurf08.png"></P
></DIV
><P
><B
>Figure 64. Solid view (left) and final rendering (right) of the Gargoyle. </B
></P
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