Subdivision Surfaces

Realsoft Graphics Oy		Subdivision Surfaces
	Geometric Primitives

Realsoft 3D's Subdivision Surface implementation is based on Catmull-Clark surfaces. However, Realsoft 3D supports rational SDS surfaces - there can be a 'weight' parameter associated with each control point. Increasing the weight pulls the corresponding surface point towards the control point in question.

A subdivision surface object is defined by a set of control points and a set of faces. Each face can refer to three or more control points.

There are many pointwise attributes that can be defined, such as color, illumination, or transparency. Also, there can be pointwise values for any user defined channel.

Vertex sharpness can be set for any set of vertices. It can be Rounded (default), Semi Sharp or Sharp. There's also a similar control for edge sharpness. Additionally, a 'Free' edge sharpness rounding can be defined numerically.

SDS objects can include multiple UV channels defining how textures are applied on the surface.

Realsoft 3D's SDS implementation also supports per face materials: a material name and a set of UV parameter values (one per vertex in the face) can be attached to any face.

SDS Properties

Handles

SDS supports a small but very powerful set of handles through which most commonly needed tools can be applied.

There are three sets of handles: point, edge and face handles, which can all be selected. When a handle is selected, it typically shows a set of sub handles. For example, when a face handle is selected, also the face normal handle is shown for the selected face.

The usual selection modifiers and the drag box selector are available when selecting SDS handles.

Point Handles

The point handles are shown when the SDS object is in the point editing mode.

Each SDS point acts as a translation handle by default.

Points can be duplicated by dragging them with the Ctrl key pressed.

The weight parameter associated with the points can be changed by dragging the point with the Alt key pressed.

The 'Move on normal' tool can be activated by dragging the surface normal handle.

The Bevel tool can be activated by dragging the end point of the surface normal handle.

Handles shown in the point editing mode

Edge Handles

The edge handles are shown when the SDS object is in the edge editing mode.

Handles shown in the edge editing mode

Face Handles

The face handles are shown when the SDS object is in the face editing mode.

Handles shown in the face editing mode

Property Gadget

The SDS property gadget has the following frames: SelectedPoints, SelectedEdges,Rendering, MultiUV, Faces.

Selected Points frame

Points - the number of vertices in the SDS object
Selected - index of the selected vertex. If more than one vertex is selected the index of the first selected vertex is shown in the conflict color.
Position - 3D position of the selected vertex.

UV - current UV channel value for the selected vertex. The current UV channel can be selected from the list in the Multi UV frame.
Attribute - list of pointwise (defined separately for each vertex) attributes. Use this to select the pointwise attribute.
Value - selected pointwise attribute value for the selected vertex.
Clear - removes the selected pointwise attribute from the SDS object.
Rational - if checked pointwise weights can be controlled. Unchecking this checkbox removes pointwise weights.
Weight - sets the weight for the selected vertex/vertices. Can be used only when the Rational checkbox is checked.
Vertex sharpness - sharpness of the selected vertices. Possible values are
- Rounded
- Semi Sharp
- Sharp
Select - selection mode, select by Point, Edge or Face.

Selected Edges frame

Edge Sharpness - sharpness of the selected edges. Possible values are
Rounded

SemiSharp

Sharp

Free
If free is selected, then the edge rounding can be set numerically.
Edge Rounding - can be set to edges that have Edge Sharpness set to Free.

Rendering Frame

Type - How the SDS object will be rendered. The possible values are

Smoothen to nurbs - the surface is rendered using bicubic NURBS patches
Smoothen to rectangles - the surface is rendered using bilinear phong shaded quadrangles
Smoothen to triangles - the surface is tessellated to phong shaded triangles

Polygonal - The original control polygon is rendered without tessellation. Normal smoothing can be turned on using the Phong shaded option described below.

Quality - Rendering quality, the higher the value, the smoother the surface. Controls how many NURBS patches are fitted into the surface.
Phong Shaded - If set, normals of a polygonally rendered SDS surface are interpolated using Phong shading making the surface appear smoothly curved. This method works well only with relatively dense control polygons.
Interpolate Boundary - If set sets maximum crease value for boundary edges (i.e. edges that are not shared be two faces).
Minimal Outlines - If set, the density of outlines appearing on the rendered surface in outline rendering mode is minimal (i.e. matches the density of the control polygon). If unset, NURBS patch fitting density defined by the Rendering Quality setting above and triangularization of polygonal surfaces are visible in rendered outlines.

Max. Displacement - If the value of this field is greater than zero, and if surface geometry shaders are mapped to the surface, the surface is displaced according to the bump height channel in ray trace rendering. 'Max. Displacement' defines the maximal amount of displacement.

The displacement value is a real distance value (the unit can be selected from 'Options/Window' pull down menu, 'Metrics' tab), so usually quite small values are sufficient (such as 0.01 meters=1 centimeter). The amount of displacement has a great impact on rendering speed, so it is wise to use a minimal 'Max. Displacement' limit value here. Note also that displacement is symmetric to both sides of the original surface. Therefore, a displacement map that is centered around zero and whose amplitude varies between -1 and 1 centimeters renders faster than a bump map whose amplitude range is from 0 to 2 cm. In former case, the 'Max Displacement' value can be 1 cm, whereas the latter case requires a limit value of 2 cm.

	Note
	Use of displacement mapping does not automatically increase the rendering accuracy to meet the new surface detail requirements. If the displacement map includes lots of details, the original surface must be reasonably dense and the rendering Quality value described above must be high enough. If rendering artifacts appear, you can apply the SDS Smooth tool to increase the control polygon density.

Multi UV frame

Channel - possible UV channels.
Add - add the selected channel as a UV channel.
Del - Delete the selected UV channel. The selection is shown in the list view gadget.
Add Default - adds the default UV channel (UV coords).
List of UV Channels added to the object.

Wrap U - If checked interpolates U to nearest modulo at the boundaries defined by Wrap Start and Wrap End. Check this if the UV space is closed in the U direction.
Wrap V - If checked interpolates V to nearest modulo at the boundaries defined by Wrap Start and Wrap End. Check this if the UV space is closed in the V direction.
Wrap Start - Minimum boundaries (U, V) for modulo wrapping. This should usually be 0.0 0.0 for texture maps.
Wrap End - Maximum boundaries (U, V) for modulo wrapping. This should usually be 1.0 1.0 for texture maps.

Faces frame

Faces - number of faces in the SDS object.
Selected Face - index of the selected face. If more than one face is selected the index of the first selected face is shown in the conflict color.
Selected faces only - if checked the Material list view below shows only those face materials and face textures that are attached to the selected faces. Otherwise all face materials and face textures are listed.

Material - shows the face material and face texture names of the selected faces or of all faces. This control has a context menu where the selected face material or face texture can be detached from the faces. If Selected faces only is checked then the face material or face textuer is detached from the selected faces. Otherwise it is detached from all the faces.
Texture - Select a image file to be used as a face texture for the selected faces. Click the Attach button to attach the face texture.
Attach - Attach the selected image file to the selected faces as a face texture.
UV - the face material or face texture UV for the selected UV vertex. Check the Select UV vertices checkbox and select a UV vertex in the UV Editor window. Now the UV control can be used to set the face material or face texture UV for that vertex numerically.
Select UV vertices - if checked UV vertices can be selected in the UV Editor. Otherwise faces can be selected.
Vertex UVs in face mode - if checked per vertex UV values are shown in the UV Editor when the SDS object is in the Face selection mode. Otherwise face material and face texture UVs are shown.

Additional Controls in The Wire Tab

Material Rendering - Defines how the SDS object is rendered in shaded mode.
- Single - Only one face material or face texture per face is rendered. This is much faster than the Full mode.
- Full - All face materials and face textures as well as mapping objects are considered. It is often preferable to use low Texture Quality settings when using this mode.
Force Tessellation - If set, triangular tessellation of faces which have more than 4 vertices is shown in wireframe drawing.


Seed Object		SunMoon Object