Add bindings for 10 high-impact missing libigl functions

[alecjacobson]

Summary

I enumerated the currently-unbound libigl functions, ranked them, and implemented Python bindings (with call tests) for the top 10 that are both straightforward to bind and high-impact.

Method

• Diffed all igl:: public headers against the set of functions already bound in src/. Result: 280 unbound headers.
• Filtered out non-candidates (type/enum/macro headers, MATLAB-style numeric helpers already covered by NumPy, IO/OpenGL/internal utilities) → 116 plausibly-bindable functions.
• Scored each on straightforwardness (1–5; 5 = dense Eigen / scalar types only, trivial wrapper) and impact (1–5; 5 = commonly-used core geometry op), reading each header to verify the actual signature.

Implemented (top 10)

function	purpose	impact
polar_svd3x3(A)	closest rotation to a 3×3 matrix (fast SVD)	★★★★
fit_rotations(S)	batched per-vertex rotation fitting (ARAP local step)	★★★★
point_simplex_squared_distance(p, V, Ele, i)	point→simplex distance + closest point + barycentric coords	★★★★
quad_planarity(V, F)	per-quad non-planarity measure	★★★★
planarize_quad_mesh(Vin, F, maxIter, threshold)	planarize a quad mesh	★★★★
smooth_corner_adjacency(V, F, threshold)	crease-aware per-corner adjacency (CSR)	★★★★
ramer_douglas_peucker(P, tol)	piecewise-linear curve simplification	★★★
connect_boundary_to_infinity(F) / (V, F)	close an open mesh via a point at infinity	★★★
path_to_edges(I, make_loop=False)	vertex path/loop → edge list	★★★
quad_edges(Q)	unique undirected edges of a quad mesh	★★★

Non-obvious wrapping details are documented in the commit message (non-deduced DIM template param on point_simplex_squared_distance; upstream int32-only instantiation of quad_edges; output-type-tied-to-input on planarize_quad_mesh).

Runners-up (rest of the top ~50, deferred)

Grouped by why they weren't in this batch:

High value but need more than a trivial wrapper (good follow-ups):

• unproject_ray, unproject_onto_mesh, unproject_on_plane, unproject_on_line — viewer/camera math (fixed-size Matrix4f/Vector4f, some with Hit/callback variants)
• frame_field_deformer, frame_to_cross_field, comb_line_field, line_field_mismatch, parallel_transport_angles — cross/frame-field design
• grad_intrinsic, lscm_hessian, normal_derivative, covariance_scatter_matrix, arap_rhs, arap_linear_block, cr_vector_laplacian/cr_vector_mass/cr_vector_curvature_correction, scalar_to_cr_vector_gradient, group_sum_matrix — return sparse operators (bindable, just larger surface)
• tetrahedralized_grid — needs the TetrahedralizedGridType enum exposed
• random_points_on_mesh_intrinsic — templated URBG parameter
• edge_midpoints, edge_vectors — depend on precomputed halfedge (E, oE) from orient_halfedges
• internal_angles_intrinsic, mapping_energy_with_jacobians, linprog, svd3x3, seam_edges, round_cone_signed_distance, piecewise_constant_winding_number, triangles_from_strip, bone_parents, collapse_small_triangles, exploded_view, box_surface_area, box_simplices, faces_first, simplify_polyhedron, outer_element, eytzinger_aabb, triangle_triangle_intersect_shared_edge/_shared_vertex, point_in_circle, projection_constraint, kkt_inverse, project_isometrically_to_plane — lower impact and/or narrower audience

Excluded as not straightforwardly bindable / redundant:

• jet, parula — redundant with the already-bound colormap()
• winding_number_antipodal — requires an Intersector class argument
• forward_kinematics, deform_skeleton, directed_edge_orientations, dqs, direct_delta_mush — std::vector<Quaterniond/Affine3d> state
• decimation/optimization internals with std::function callbacks or AABB/quadric state (collapse_least_cost_edge, qslim_optimal_collapse_edge_callbacks, line_search, flip_avoiding_line_search, pso, random_search, shapeup, screen_space_selection, variable_radius_offset, topological_hole_fill, unzip_corners, extract_non_manifold_edge_curves, …)

Testing

Added test_polar_svd3x3_and_fit_rotations, test_point_simplex_squared_distance, test_quad_mesh_helpers, test_ramer_douglas_peucker, test_path_to_edges_and_connect_boundary, and test_smooth_corner_adjacency to tests/test_all.py. Full suite passes locally:

104 passed

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