v1.5.0

Highlights

• Implement "Geometric Contact Potential" [Huang et al. 2025] by @Huangzizhou in #191
• Implement "Offset Geometric Contact" [Chen et al. 2025] by @zfergus in #192
• Implement fully parallel LBVH Broad Phase by @zfergus in #188
• Add geometry utilities for collision normals, signed distances, and dihedral angles with gradients and Hessians.

What's Changed

New Formulations

• Geometric Contact Potential (GCP) by @Huangzizhou in #191
  • The implementation includes the collision and friction potential with gradients and Hessians.
  • Tutorial available here.
• Offset Geometric Contact (OGC) by @zfergus in #192
  • OGC is a penetration-free contact model that replaces continuous collision detection (CCD) with a trust-region-based approach.
  • New Namespace: Introduced ipc::ogc to encapsulate OGC-specific functionality.
  • Trust Region Implementation:
    • Added TrustRegion class (trust_region.hpp, trust_region.cpp) to manage per-vertex conservative bounds.
    • Implemented warm_start_time_step to initialize the trust region and handle initial predictions.
    • Implemented filter_step to scale optimization steps ensuring vertices stay within safe bounds.
    • Implemented update and update_if_needed to dynamically resize trust regions based on motion.
  • Feasible Region Logic:
    • Added feasible_region.hpp and feasible_region.cpp containing geometric predicates (e.g., check_vertex_feasible_region, is_edge_edge_feasible) to verify if primitives are within valid non-penetrating regions.
    • Integrated feasible region checks into the NormalCollisions class to filter out invalid collision candidates. Enabled via set_collision_set_type(NormalCollisions::CollisionSetType::OGC).
  • Step Scaling: Unlike the original paper's projection method, TrustRegion::filter_step scales the descent direction $\beta$ to keep vertices on the trust region boundary. This preserves the descent direction, ensuring compatibility with line-search-based solvers.
  • Tutorial available here.

Broad Phase

• Parallel CPU LBVH implementation by @zfergus in #188
  • New broad phase collision detection method with memory optimizations on the AABB structure.
  • LBVH Broad Phase:
    • Implemented LBVH class in src/ipc/broad_phase/lbvh.hpp, providing a Linear Bounding Volume Hierarchy method for broad phase collision detection.
    • Fully parallel build and traversal routines using Intel TBB.
    • SIMD optimizations for AABB overlap tests.
    • Faster than the existing BVH method and all other broad phase methods in IPC Toolkit for large scenes.
      • More than 3x faster to build.
      • Up to 1.5x faster for candidate detection.
      • Detailed performance charts available below.
    • Added python/examples/lbvh.py to demonstrate usage and visualization.
  • ⚡ Enhancements
    • Performance Optimizations:
      • Added DefaultInitAllocator to reduce overhead when allocating large arrays of POD types.
      • Replaced std::vector<AABB> with std::vector<AABB, DefaultInitAllocator<AABB>>.
    • Memory Optimization:
      • Switched AABB::min and AABB::max from ArrayMax3d to Eigen::Array3d.
      • Result: Reduces sizeof(AABB) from 76 to 64 bytes, allowing AABB to fit into a single cache line (assuming 64-byte lines).
    • Replaced hardware rounding in AABB::conservative_inflation with software rounding using std::nextafter.
  • 💥 Breaking Changes
    • API & Structural Changes:
      • Moved dimension variable: Removed dim from AABB and moved it to BroadPhase to handle 2D/3D data more cleanly. dim is now set in BroadPhase::build.
      • Handle 2D data by setting AABB's z-components to zero.
      • Constructor Removal: Removed the AABB default constructor and the initialization of AABB::vertex_ids.
      • Type Change: Changed to_3D in ipc/utils/eigen_ext.hpp to operate on Eigen::Array types instead of Eigen::Vector.
    • Deprecated BVH class in favor of the new LBVH class for better performance on large scenes.
• Refactor BroadPhase to Build from Vertex Boxes Directly in #187
• Rename sweep_and_tiniest_queue.cpp to .cu file by @iiiian in #203
• Fix vertex id assignment by @iiiian in #204
  • Fix vertex id assignment logic in SweepAndTiniestQueue.
• Replace optional const shared_ptr<BroadPhase>& parameters with BroadPhase* in #205
  • Change make_default_broad_phase to return a unique_ptr
• Pass parameters to Scalable CCD Narrow-Phase by @antoinebou12 in #208
  • Replace hardcoded TightInclusionCCD::DEFAULT_TOLERANCE and TightInclusionCCD::DEFAULT_MAX_ITERATION with narrow_phase.tolerance and narrow_phase.tolerance if passed a TightInclusionCCD object.
  • If narrow_phase_ccd is not a TightInclusionCCD instance, we fall back to default values to preserve backward compatibility.
• Add SIMD support via xsimd library in #207
  • Cross-platform SIMD (Single Instruction, Multiple Data) support using the xsimd library in the LBVH code.
  • Update the IPC_TOOLKIT_WITH_SIMD to be enabled by default, and improve CMake logic to detect SIMD capabilities and configure the build accordingly.
  • Disable Eigen's internal vectorization to avoid crashes on Linux.

Math and Geometry Utilities

• Add normal computation and Jacobian methods for collision candidates in #182
• Collect normal utilities into geometry/normal files in #197
• Organize geometry and math utilities into geometry and math folders in #198
• Add signed distance computations for point-plane, point-line, and line-line geometries in #206
• Optimized edge_edge_mollifier.cpp with FMA operator in gradient calculations.

Miscellaneous

• Updated dependencies:
  • Bump Abseil from 20250512.1 to 20260107.0
  • Bump Catch2 from v3.8.1 to v3.12.0
  • Bump Eigen from 3.4.0 to 5.0.1
  • Bump JSON from v3.11.2 to v3.12.0
  • Bump libigl from 89267b4a80b1904de3f6f2812a2053e5e9332b7e to v2.6.0
  • Bump TBB from v2022.1.0 to v2022.3.0
  • Bump Pybind11 from v2.13.1 to v3.0.1
  • Bump robin-map from v1.4.0 to v1.4.1
  • Bump spdlog from v1.15.3 to v1.17.0
• Make most dependencies private
  • Added a figure for default dependencies of the ipc::toolkit library: https://ipctk.xyz/about/dependencies.html
  • Refactored BVH class to use unique_ptr to hide SimpleBVH
  • Updated Sweep and Prune and Sweep and Tiniest Queue classes to use a Pimpl pattern for encapsulation.
  • Mark tsl::robin_map and absl::hash as private dependencies in CMake. Update the dependency documentation accordingly.
  • Convert SpatialHash to PImpl idiom to hide tsl::robin_map and absl::hash from the public API.
• Add Clang Tidy check
  • Added a .clang-tidy configuration file with a comprehensive set of checks, exclusions, naming conventions, and options to enforce modern C++ practices and treat all warnings as errors.
  • Introduced a GitHub Actions workflow (.github/workflows/clang-tidy-check.yml) to automatically run Clang-Tidy on relevant files for every push and pull request, improving code quality and review automation.
• Simplify CMake CUDA setup by @iiiian in #201
  • Disable CUDA builds by default.
  • Bump CMake minimum version to 3.24 to support CMAKE_CUDA_ARCHITECTURES="native"
• Add performance profiling utilities in #188
  • Added a (optional) profiler utility (src/ipc/utils/profiler.hpp) to measure/record metrics with CSV output support.
  • Added Nlohmann JSON as a dependency for profiler storage.
  • Use IPC_TOOLKIT_WITH_PROFILER CMake option to enable/disable profiling.
• Refactor to use Eigen::ConstRef for vertices in #200

New Contributors

• @iiiian made their first contribution in #201

Full Changelog: v1.4.0...v1.5.0