Lagrange Release v6.0.0

Highlights

• Generic mesh API that works in 2D, 3D, triangles/quad/hybrid mesh using the same mesh type.
• Simple API based on std::span<> (assumes continuous memory buffers)
• Generic copy-on-write attributes (per vertex, facet, edge, etc.)
• Separate views.h provides Eigen "views" over mesh buffers.
• Mesh header only pulls STL headers (, <string_view>, and -- last one can be avoided easily).
• Efficient memory storage: regular meshes only need 2 buffers (vertex pos, facet indices), while hybrid meshes uses an additional offset buffer.
• Use PIMPL idiom to hide internal mesh attribute manager.
• Mesh attribute can wrap external buffers (including const buffers). Policies determine write/growth behavior.
• Efficient buffer growth via std::vector<>.
• Use explicit template instantiation to enforce strict separation of declaration/definition (faster compile times)
• Use X macros to facilitate explicit template instantiation of predetermined types
• Export attributes into shared_ptr for lifetime management.
• Full Doxygen documentation.
• Zero compiler warnings with much stricter warning flags than before.
• C++17 is now the minimum required standard.

Features

Attributes

• Generic attribute class, templated only by scalar type.
• Versatile, low-level but safe interface based on std::span<>.
• Use explicit template instantiation to separate .cpp and .h
• Support wrapping external buffers (const and non-const). A policy controls write behavior to const buffers.
• Support wrapping external buffers with larger capacity. A policy controls growth behavior of external buffers.
• Support various attribute usage tags. VertexIndex, FacetIndex, etc. will remap indices accordingly when resizing/reordering.
• Indexed attributes as a pair of (indices, value) attributes
• Set default value used for attribute growth (e.g. invalid index, -1, etc.).
• Unit tests with 100% coverage

Mesh

• Copy-on-write allows the new mesh class to have efficient "pass-by-value" semantic (a mesh can be copied/moved efficiently).
• Generic mesh API supporting arbitrary dimension & arbitrary polygonal facets.
• Dynamic mesh supporting insertion & deletion of vertices/facets.
  • Add vertices/facets extend existing attribute buffers.
  • Efficient batch element removal (using either a list/mask of elements to remote).
  • Efficient in-place reordering/reindexing after element removal.
  • Methods to clear vertices/facets
• Mesh attributes
  • Access attributes via names (<string_view>) or attribute ids (avoid a hash map lookup).
  • Easy read/write references to mesh vertices and facets indices.
  • Prevent creation of reserved attribute names (starting with "$").
  • Export attribute buffer into a shared_ptr.
• Mesh edges
  • Initialize mesh edges using user-given ordering.
  • Additional connectivity attribute for navigation.
  • Preserve attributes when resizing/reindexing mesh elements
• Mesh IO for .obj files
  • Basic mesh IO for positions + indices
  • Extended mesh IO with uv and normals

Views

• Convenient "Eigen" map views over mesh attributes: compatible with libigl functions (V, F).
• Convenient views for mesh vertices/facets + generic views for custom attributes.

Visitors

• Provide foreach_attribute methods to visit all mesh attributes.
• Sequential and parallel iteration.
• BitField for iterating over attributes of a certain type.
• Filter indexed and non-indexed attributes via if constexpr or template args.
• foreach_xxx_around visitors use function_ref<> rather than templated functions.