Triangular Patches for Loop Subdivision

Support for the drawing and evaluation of Loop subdivision meshes with triangular patches was added. This includes the full set of Far and Osd interfaces for both evaluation and drawing.

The feature set supported for Loop subdivision now matches that of Catmark, including creases, face-varying patches, non-manifold topology, etc.

The long standing requirement that Loop meshes be purely triangular remains, as Loop subdivision is not defined for non-triangular faces. And as is the case with the use of the Catmark scheme, application of Loop subdivision to dense, poorly modeled meshes may lead to unexpectedly poor performance and/or surface quality.

The patch representation used for Loop subdivision is intended to exactly match the underlying limit surface where regular, and so uses quartic triangular Box-splines. This is in contrast to approaches that use simpler patches to approximate the Loop limit surface everywhere. As with Catmark, Gregory patches are used to approximate irregular areas. Though other choices are available that compromise surface quality in favor of improved performance, they may be less effective with Loop than they are with Catmark.

Major Improvements to Introductory Documentation

A significant rewrite of the Subdivision Surfaces page is included in this release. The new documentation emphasizes the piecewise parametric surface nature of subdivision surfaces and the implications of supporting arbitary topology.

As a true surface primitive, the distinction between the control points and the limit surface and the corresponding operations of subdivision and tessellation that are applied to them is made clear.

Sparse Patch Tables

Interfaces in Far for the construction of PatchTables and the required adaptive refinement have been extended to apply to an arbitrary subset of faces. This allows patches for either large meshes or meshes that may otherwise benefit from some kind of partioning (e.g. areas of static and dynamic topology) to be managed in an arbitrary number of groups. In the extreme, a PatchTable forming the tree of patches for a single base face can be constructed.

Client data buffers for the base mesh do not need to be partitioned and base mesh topology can be shared by multiple instances of Far::TopologyRefiner used to create corresponding instances of Far::PatchTables.

See the new Far tutorial 5.2 for a simple example.

Support for Double Precision in Far

Classes and interfaces in Far have been adapted to allow support for double precision via templates parameterized for float or double. Class templates for major classes such as Far::StencilTable have been introduced and the original classes preserved for compatibility. Other classes such as Far::PatchTable have had methods overloaded or replaced with template functions to support both single and double precision. Internally, all use of floating point constants and math library functions has been adapted to maximize accuracy appropriate to the precision of the template instance.

Interfaces in Osd have not been extended. The extensions in Far provide the basis for extensions in Osd, but demand is limited. For those benefiting from such Osd extensions, contributions are welcomed.

See the revised Far tutorial 5.1 that constructs a Far::PatchTable for a simple example.

Far extensions for triangular patches

• enum PatchDescriptor::Type::GREGORY_TRIANGLE
• PatchParam::NormalizeTriangle()
• PatchParam::UnnormalizeTriangle()
• PatchParam::IsTriangleRotated()

Construction and refinement of topology

• overloaded TopologyRefinerFactory::Create()
• extensions to TopologyRefiner::RefineAdaptive()

Construction and interface of Far::PatchTable

• overloaded PatchTableFactory::Create()
• PatchTableFactory::GetRefineAdaptiveOptions()
• member PatchTableFactory::Options::includeBaseLevelIndices
• member PatchTableFactory::Options::includeFVarBaseLevelIndices
• member PatchTableFactory::Options::generateVaryingTables
• member PatchTableFactory::Options::generateVaryingLocalPoints
• member PatchTableFactory::Options::setPatchPrecisionDouble
• member PatchTableFactory::Options::setFVarPatchPrecisionDouble
• PatchTable::GetFVarPatchDescriptorRegular()
• PatchTable::GetFVarPatchDescriptorIrregular()
• PatchTable::GetFVarValueStride()

Construction and use of Far stencil tables

• overloaded StencilTable::UpdateValues()
• enum LimitStencilTableFactory::Mode
• member LimitStencilTableFactory::Options::interpolationMode
• member LimitStencilTableFactory::Options::fvarChannel

Far class templates for double precision

• class StencilReal
• class StencilTableReal
• class StencilTableFactoryReal
• class LimitStencilReal
• class LimitStencilTableReal
• class LimitStencilTableFactoryReal
• class PrimvarRefinerReal

Far member functions converted to templates for double precision

• PatchParam::Normalize()
• PatchParam::Unnormalize()
• PatchTable::EvaluateBasis()
• PatchTable::EvaluateBasisVarying()
• PatchTable::EvaluateBasisFaceVarying()
• PatchTable::GetLocalPointStencilTable()
• PatchTable::GetLocalPointVaryingStencilTable()
• PatchTable::GetLocalPointFaceVaryingStencilTable()
• PatchMap::FindPatch()

Osd::MeshBits

• enumeration MeshEndCapBilinearBasis

Osd::PatchArray

• GetDescriptorRegular()
• GetDescriptorIrregular()
• GetPatchTyperRegular()
• GetPatchTyperIrregular()
• GetStride()

Osd extensions for patch evaluation common to all shaders

• struct OsdPatchArray and OsdPatchArrayInit()
• struct OsdPatchCoord and OsdPatchCoordInit()
• struct OsdPatchParam and OsdPatchParamInit()
• OsdPatchParamGetFaceId()
• OsdPatchParamGetU()
• OsdPatchParamGetV()
• OsdPatchParamGetTransition()
• OsdPatchParamGetBoundary()
• OsdPatchParamGetNonQuadRoot()
• OsdPatchParamGetDepth()
• OsdPatchParamGetParamFraction()
• OsdPatchParamIsRegular()
• OsdPatchParamIsTriangleRotated()
• OsdPatchParamNormalize()
• OsdPatchParamUnnormalize()
• OsdPatchParamNormalize(Triangle)
• OsdPatchParamUnnormalizeTriangle()
• OsdEvaluatePatchBasisNormalized()
• OsdEvaluatePatchBasis()

Osd extensions for patch tessellation common to all shaders

• OsdInterpolatePatchCoordTriangle()
• OsdComputePerPatchVertexBoxSplineTriangle
• OsdEvalPatchBezierTriangle()
• OsdEvalPatchGregoryTriangle()
• OsdGetTessLevelsUniformTriangle()
• OsdEvalPatchBezierTessLevels()
• OsdEvalPatchBezierTriangleTessLevels()
• OsdGetTessParameterizationTriangle()

Improvements

• Added new build script (GitHub #1068)
• Added support for newer DirectX SDKs (GitHub #1066)
• Patch arrays extended to support combined regular and irregular types (GitHub #995)
• Far::PatchTables and adaptive refinement supported for Bilinear scheme (GitHub #1035)
• New Far::PatchTableFactory method to determine adaptive refinement options ((GitHub #1047)
• New Far::PatchTableFactory options to align primvar buffers of uniform tables (GitHub #986)
• Far::StencilTable::UpdateValues() overloaded to support separate base buffer (GitHub #1011)
• Far::LimitStencilTableFactory updated to create face-varying tables (GitHub #1012)
• Regular patches on boundaries no longer require additional isolation (GitHub #1025)
• Inclusion of OpenSubdiv header files in source code now consistent (GitHub #767)
• Re-organization of and additions to Far tutorials (GitHub #1083)
• Examples now use common command-line conventions and parsing (GitHub #1056)

Bug Fixes

• Fixed Far::PrimvarRefiner internal limitFVar() prototype (GitHub #979)
• Fixed Far::StencilTable append when base StencilTable empty (GitHub #982)
• Patches around non-manifold vertices now free of cracks (GitHub #1013)