SubDMesh.md

SubDMesh Class

Overview

SubDMesh (Subdivision Mesh) represents a modern mesh object capable of smoothing, creasing, and complex organic modeling. Unlike legacy PolygonMesh, it supports n-gon faces, varying smoothness levels, and edge/vertex weighting.

Namespace

Autodesk.AutoCAD.DatabaseServices

Inheritance Hierarchy

System.Object
  └─ RXObject
      └─ DBObject
          └─ Entity
              ├─ SubDMesh

Key Properties

Property	Type	Description
SubdivisionLevel	int	Current smoothness level (0=unsmoothed).
VertexCount	int	Number of vertices.
FaceCount	int	Number of faces.
Volume	double	Volume (if watertight).
SurfaceArea	double	Surface area.

Key Methods

Method	Return Type	Description
SetSubdivisionLevel(int)	void	Sets smoothness.
SetBox(...)	void	Creates a mesh box.
SetSphere(...)	void	Creates a mesh sphere.
SubdivideFace(int)	void	Refines a specific face.
ExtrudeFaces(...)	void	Extrudes faces.

Code Examples

Example 1: Creating a Mesh Box

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    BlockTableRecord btr = tr.GetObject(db.CurrentSpaceId, OpenMode.ForWrite) as BlockTableRecord;
    
    SubDMesh mesh = new SubDMesh();
    // 10x10x10 box with 4x4x4 subdivisions
    mesh.SetBox(10, 10, 10, 4, 4, 4);
    
    btr.AppendEntity(mesh);
    tr.AddNewlyCreatedDBObject(mesh, true);
    
    tr.Commit();
}

Example 2: Smoothing a Mesh

mesh.SetSubdivisionLevel(2); // Smooths the mesh geometry

Example 3: Defining Custom Mesh (Vertices/Faces)

Point3dCollection vertices = new Point3dCollection();
vertices.Add(new Point3d(0,0,0));
vertices.Add(new Point3d(10,0,0));
vertices.Add(new Point3d(0,10,0));
// ...

Int32Collection faceCounts = new Int32Collection();
faceCounts.Add(3); // Triangle

Int32Collection faceIndices = new Int32Collection();
faceIndices.Add(0); faceIndices.Add(1); faceIndices.Add(2); // Vertex indices

SubDMesh mesh = new SubDMesh();
mesh.SetSubDMesh(vertices, faceIndices, faceCounts.Count);

Example 4: Converting to Solid

// SubDMesh can be converted to Solid3d if it encloses a volume
if (mesh.Watertight)
{
    Solid3d sol = mesh.ConvertToSolid(false, false);
    // Add sol to database...
}

Example 5: Surface Conversion

// Convert to Surface (NURBS)
Autodesk.AutoCAD.DatabaseServices.Surface surf = mesh.ConvertToSurface(false, false);

Example 6: Iterating Vertices

// Access vertices directly
// Warning: This can be large
foreach (Point3d pt in mesh.Vertices)
{
    // ...
}

Example 7: Creasing Edges

// Apply crease to maintain sharp edges during smoothing
FullSubentityPath[] edges = ...; // Need to identify edges
mesh.SetCrease(edges, 1.0); // Full crease

Example 8: Extruding a Face

// Advanced: Extruding a subentity face
FullSubentityPath facePath = ...;
mesh.ExtrudeFaces(new[] { facePath }, 5.0, 0.0);

Best Practices

1. Watertight Check: Check Watertight property before attempting volume calculations or solid conversion.
2. Level of Detail: High SubdivisionLevel exponentially increases vertex count. Keep it low for performance.
3. Subentities: Manipulating individual faces/edges requires identifying them via GetSubentPathsAtGsMarker or similar selection mechanisms.

Related Objects

• Solid3d
• PolygonMesh (Legacy)

References

• Autodesk SubDMesh Reference