Manual/Subsurf Modifier
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Subdivision Surfaces
Mode: Any Mode
Panel: Editing Context → Modifiers
Hotkey: F9 (Panel) Shift O (Toggle SubSurf in Object Mode)
Description
A Subdivision Surface is a method of subdividing the faces of a mesh to give a smooth appearance, to enable modelling of complex smooth surfaces with simple, low-vertex meshes. This allows high resolution Mesh modelling without the need to save and maintain huge amounts of data and gives a smooth organic look to the object. 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 SubSurf.
Options
SubSurf is a Modifier. To add it to a mesh, press Add Modifier and select Subsurf from the list.
- Levels defines the display resolution, or level of subdivision.
- Render Levels is the levels used during rendering. This allows you to keep a fast and lightweight approximation of your model when interacting with it in 3D, but use a higher quality version when rendering.
- To view and edit the results of the subdivision ("isolines") on the Editing Cage while you're editing the mesh, click in the gray circle next to the arrows for moving the modifier up and down the stack. This lets you grab the points as they lie in their new subdivided locations, rather than on the original mesh.
- Optimal Draw restricts the wireframe display to only show the original mesh cage edges, rather than the subdivided result to help visualisation.
You can also use Shift O if you are in ObjectMode to switch Subsurf On or Off. The Subsurf level can also be controlled via Ctrl 1 to Ctrl 4, but this only affects the visualization sub-division level.
Hints
A SubSurfed Mesh and a NURBS surface have many points in common such as they both rely on a "coarse" low-poly "mesh" to define a smooth "high definition" surface, however, there are notable differences:
- 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.
- 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.
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.
Examples
SubSurfed Suzanne shows a series of pictures showing various different combinations of Subsurf options on a Suzanne Mesh.
SubSurf of simple square and triangular faces. 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 each square or triangular face.
It is evident how each single quadrilateral face produces 4n faces in the SubSurfed mesh. n is the SubSurf level, or resolution, while each triangular face produces 3⋅4(n-1) new faces (SubSurf of simple square and triangular faces.). 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.
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. A Gargoyle base mesh (left) and pertinent level 2 SubSurfed Mesh (right). and Solid view (left) and final rendering (right) of the Gargoyle. show an example of what can be done with Blender SubSurfs.
Limitations & Work-arounds
Blender's subdivision system is based on the Catmull-Clark 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.
This is not an issue for the shape itself, as Side view of subsurfed meshes. With random normals (top) and with coherent normals (bottom) shows, but it is an issue in the rendering phase and in solid mode, where abrupt normal changes can produce ugly black lines (Solid view of SubSurfed meshes with inconsistent normals (top) and consistent normals (bottom).).
Use the Ctrl N command in EditMode, with all vertices selected, to recalculate the normals to point outside.
In these images the face normals are drawn cyan. You can enable drawing normals in the EditButtons (F9) menu.
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. From the Blender point of view,
it is a mesh where there are edges belonging to more than two faces.
A "Non-Manifold" mesh 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.
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.
Use these two hints to tell whether a mesh is "Non Manifold":
- The Recalculation of normals leaves black lines somewhere
- The "Decimator" tool in the Mesh Panel refuses to work stating that the mesh is "Non Manifold"
Weighted creases for subdivision surfaces
Mode: Edit Mode (Mesh)
Panel: 3D View → Transform Properties
Hotkey: Shift E or N (Transform Properties Panel)
Menu: Mesh → Edges → Crease Subsurf
Description
Weighted edge creases for subdivision surfaces allows you to change the way Subsurf subdivides the geometry to give the edges a smooth or sharp appearance.
Options
The crease weight of selected edges can be changed interactively by using Shift E and moving the mouse towards or away from the selection. Or use Transform Properties (N) and enter the value directly.
You can enable an indication of your edge sharpness by enabling Draw Creases. See (Mesh Tools 1 panel).
 Transform Properties |  Mesh Tools 1 panel |
Examples
The sharpness value on the edge is indicated as a variation of the brightness on the edge. If the edge has a sharpness value of 1.0, the edge will have a brighter color, and if sharpness value is 0.0, the edge will not be so bright.
 Edge sharpness 0.0 |  Edge sharpness 1.0 |
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