Merge pull request #300 from libigl/claude-edits

Add centroid binding and test [claude generated]

Author: alecjacobson

memory/MEMORY.md

@@ -0,0 +1,26 @@
+# libigl-python-bindings memory
+
+## Project
+Python bindings for libigl C++ geometry library using nanobind + scikit-build-core.
+C++ libigl source lives at `build/_deps/libigl-src/include/igl/` (fetched by CMake).
+
+## Binding Architecture
+- Each `src/<name>.cpp` → corresponds to `build/_deps/libigl-src/include/igl/<name>.h`
+- CMake globs all `.cpp` files, generates `BINDING_DECLARATIONS.in` / `BINDING_INVOCATIONS.in`, `module.cpp` includes them — adding a `.cpp` auto-registers it
+- Types centralized in `include/default_types.h`: `Numeric=double`, `Integer=int64_t`, `RowMajor`
+- Zero-copy input: `nb::DRef<const Eigen::MatrixXN>` (requires C-contiguous float64)
+- Multiple C++ output params → `std::make_tuple(...)` → Python tuple unpacking
+- Sparse output: `Eigen::SparseMatrixN` + `<nanobind/eigen/sparse.h>` → scipy CSR automatically
+
+## Submodules
+- `src/` → `igl` (core, MPL2)
+- `src/copyleft/` → `igl.copyleft` (GPL)
+- `src/copyleft/cgal/` → `igl.copyleft.cgal`
+- `src/embree/` → `igl.embree`
+- `src/triangle/` → `igl.triangle`
+
+## Key Gotchas
+- numpy `int32`/`float32` silently copies; always use `int64`/`float64` in tests
+- In-place mutation: use `Eigen::Ref<>` + `.noconvert()` on the arg
+- Class templates must be typedef'd to concrete type before `nb::class_<>`
+- Sparse inputs must be `scipy.sparse.csr_matrix`

pyproject.toml

@@ -13,7 +13,7 @@ build-backend = "scikit_build_core.build"
 
 [project]
 name = "libigl"
-version = "2.6.2.dev0"
+version = "2.6.3.dev0"
 description = "libigl: A simple C++ geometry processing library"
 readme = "README.md"
 requires-python = ">=3.8"

src/centroid.cpp

@@ -0,0 +1,40 @@
+#include "default_types.h"
+#include <igl/centroid.h>
+#include <nanobind/nanobind.h>
+#include <nanobind/eigen/dense.h>
+#include <nanobind/stl/tuple.h>
+
+namespace nb = nanobind;
+using namespace nb::literals;
+
+namespace pyigl
+{
+  auto centroid(
+    const nb::DRef<const Eigen::MatrixXN> &V,
+    const nb::DRef<const Eigen::MatrixXI> &F)
+  {
+    Eigen::VectorXN c;
+    Numeric vol;
+    igl::centroid(V,F,c,vol);
+    return std::make_tuple(c,vol);
+  }
+}
+
+void bind_centroid(nb::module_ &m)
+{
+  m.def(
+    "centroid",
+    &pyigl::centroid,
+    "V"_a,
+    "F"_a,
+R"(Computes the centroid and enclosed volume of a closed mesh using a surface
+integral.
+
+@param[in] V  #V by dim list of rest domain positions
+@param[in] F  #F by 3 list of triangle indices into V
+@return c    dim vector of centroid coordinates
+@return vol  total volume of solid
+
+\see moments
+)");
+}

tests/test_all.py

@@ -789,6 +789,25 @@ def test_find_cross_field_singularities(icosahedron):
     # theorem, so we skip this check for now.
     # assert np.sum(singularityIndex3) == 2 * 4 # Euler characteristic * 4-rosy fields
 
+def test_centroid():
+    # Icosahedron is centered at origin, so centroid should be near zero
+    V, F = igl.icosahedron()
+
+    # Overload returning both centroid and volume
+    c, vol = igl.centroid(V, F)
+    assert c.shape == (3,)
+    assert c.dtype == np.float64
+    assert isinstance(vol, float)
+    assert np.allclose(c, np.zeros(3), atol=1e-10)
+    assert vol > 0
+
+    # Known geometry: unit tetrahedron centroid should be at (0.25, 0.25, 0.25)
+    V_tet = np.array([[0,0,0],[1,0,0],[0,1,0],[0,0,1]], dtype=np.float64)
+    F_tet = np.array([[2,1,0],[1,3,0],[3,2,0],[2,3,1]], dtype=np.int64)
+    c_tet, vol_tet = igl.centroid(V_tet, F_tet)
+    assert np.allclose(c_tet, [0.25, 0.25, 0.25], atol=1e-10)
+    assert np.isclose(vol_tet, 1.0/6.0, atol=1e-10)
+
 def test_comb_frame_field(icosahedron):
     V,F = icosahedron