Hierarchical Subdivision Surfaces

Subdivision Surfaces

Hierarchical Subdivision Surfaces

Hierarchical subdivision surface rendering is fully supported by mental ray. It implements the Loop subdivision scheme for triangle meshes, and the Catmull-Clark subdivision scheme for quadrilateral meshes. The following features are available:

C/C++ API for subdivision surface construction and manipulation. This API can be used by geometry shaders to create renderable subdivision surface objects.
Smooth, dart, conic, cusp and corner vertex features.
Crease edges with fractional sharpness.
Adaptive local refinement and tessellation, visibility culling.
Texturing with unlimited number of texture spaces, motion blur.
Trim regions by trim edge specification.

Advanced modeling operations for hierarchical subdivision surfaces are available as optional components, provided in a separate library. It includes:

Multi-resolution editing with wavelet decomposition and variable data-dependent smoothing.
Conversion of subdivision surfaces to NURBS.

Catmull-Clark Mesh Geometry

mental ray provides a simplified and fast subdivision algorithm which is optimized for smoothing of arbitrary polygon meshes: the polygons in such a mesh can have an arbitrary number of edges. Hierarchies are not supported in this representation. In the subdivision process each polygon is split into quadrilaterals using generalized Catmull-Clark subdivision rules. Mixed meshes consisting only of triangles and quads are directly subdivided using specialized rules. Subdivision rules are applied to both positions and texture coordinates for highest mapping quality.

This mesh representation is well suited for fine displacement, because it does not suffer from inherent artifacts when displacing coarse polygon meshes.

Note: for both types of subdivision geometry, mental ray performs displacement mapping during computation of the limit surface, using a single approximation setting for the entire tessellation.