[python] fix warp callback (#674)

* [python] fix warp callback

I recently broke this making it a no-op due to
the vec reference becoming a by-value copy in python
callback. This fix provides a simple adapter like
we had before allowing python to return modified
values from the callback.

* update torus_knot.py demo to expose both warp modes

* add torus_knot.py to pytest

* use pytest in github CI

* add pytest to flake.nix

.github/workflows/manifold.yml

@@ -23,7 +23,7 @@ jobs:
       run: |
         sudo apt-get -y update
         DEBIAN_FRONTEND=noninteractive sudo apt install -y libglm-dev libgtest-dev libassimp-dev git libtbb-dev libthrust-dev pkg-config libpython3-dev python3 python3-distutils python3-pip lcov
-        pip install trimesh
+        pip install trimesh pytest
     - uses: actions/checkout@v3
       with:
         submodules: recursive
@@ -42,6 +42,7 @@ jobs:
         ./manifold_test
         cd ../../
         python3 bindings/python/examples/run_all.py -e
+        python3 -m pytest
     - name: Coverage Report
       # only do code coverage for default sequential backend, it seems that TBB
       # backend will cause failure

bindings/python/examples/test_torus_knot.py

@@ -1,6 +1,6 @@
-# %%
-import numpy as np
 from manifold3d import *
+import numpy as np
+import pytest
 
 # Creates a classic torus knot, defined as a string wrapping periodically
 # around the surface of an imaginary donut. If p and q have a common
@@ -9,7 +9,7 @@ from manifold3d import *
 # handling of triangles.
 
 
-def run():
+def run(warp_single=False):
     # The number of times the thread passes through the donut hole.
     p = 1
     # The number of times the thread circles the donut.
@@ -72,16 +72,26 @@ def run():
         m2[:, 3, 0] = majorRadius
         m3 = ax_rotate(2, psi)
 
-        v = v[:, None, :] @ (m1 @ m2 @ m3)
-        return v[:, 0, :3]
+        v = v[:, None, :] @ m1 @ m2 @ m3
+        pts[:] = v[:, 0, :3]
 
     def func_single(v):
-        pts = np.array(v)[None, :]
-        pts = func(pts)
-        return tuple(pts[0])
+        pts = np.array([v])
+        func(pts)
+        return pts[0]
 
-    return circle.revolve(int(m)).warp_batch(func)
-    # return circle.revolve(int(m)).warp(func_single)
+    if warp_single:
+        return circle.revolve(int(m)).warp(func_single)
+    else:
+        return circle.revolve(int(m)).warp_batch(func)
+
+
+@pytest.mark.parametrize("warp_single", [True, False])
+def test_warp(warp_single):
+    m = run(warp_single=warp_single)
+    assert m.volume() == pytest.approx(20785.76)
+    assert m.surface_area() == pytest.approx(11176.8)
+    assert m.genus() == 1
 
 
 if __name__ == "__main__":

bindings/python/manifold3d.cpp

@@ -271,8 +271,14 @@ NB_MODULE(manifold3d, m) {
             return self.Rotate(v.x, v.y, v.z);
           },
           nb::arg("v"), manifold__rotate__v.c_str())
-      .def("warp", &Manifold::Warp, nb::arg("warp_func"),
-           manifold__warp__warp_func)
+      .def(
+          "warp",
+          [](const Manifold &self,
+             std::function<glm::vec3(glm::vec3)> warp_func) {
+            // need a wrapper because python cant modify a reference in-place
+            return self.Warp([&warp_func](glm::vec3 &v) { v = warp_func(v); });
+          },
+          nb::arg("warp_func"), manifold__warp__warp_func)
       .def("warp_batch", &Manifold::WarpBatch, nb::arg("warp_func"),
            manifold__warp_batch__warp_func)
       .def(
@@ -610,8 +616,14 @@ NB_MODULE(manifold3d, m) {
            cross_section__mirror__ax)
       .def("transform", &CrossSection::Transform, nb::arg("m"),
            cross_section__transform__m)
-      .def("warp", &CrossSection::Warp, nb::arg("warp_func"),
-           cross_section__warp__warp_func)
+      .def(
+          "warp",
+          [](const CrossSection &self,
+             std::function<glm::vec2(glm::vec2)> warp_func) {
+            // need a wrapper because python cant modify a reference in-place
+            return self.Warp([&warp_func](glm::vec2 &v) { v = warp_func(v); });
+          },
+          nb::arg("warp_func"), cross_section__warp__warp_func)
       .def("warp_batch", &CrossSection::WarpBatch, nb::arg("warp_func"),
            cross_section__warp_batch__warp_func)
       .def("simplify", &CrossSection::Simplify, nb::arg("epsilon") = 1e-6,

flake.nix

@@ -60,7 +60,7 @@
                 glm
                 ninja
                 (python39.withPackages
-                  (ps: with ps; [ trimesh ]))
+                  (ps: with ps; [ trimesh pytest ]))
                 gtest
               ]) ++ build-tools;
               cmakeFlags = [
@@ -74,6 +74,7 @@
                 ./manifold_test
                 cd ../../
                 PYTHONPATH=$PYTHONPATH:$(pwd)/build/bindings/python python3 bindings/python/examples/run_all.py
+                PYTHONPATH=$PYTHONPATH:$(pwd)/build/bindings/python python3 -m pytest
                 cd build
               '';
             };
@@ -155,12 +156,14 @@
               ];
               checkInputs = [
                 trimesh
+                pytest
               ];
               format = "pyproject";
               dontUseCmakeConfigure = true;
               doCheck = true;
               checkPhase = ''
                 python3 bindings/python/examples/run_all.py
+                python3 -m pytest
               '';
             };
           };

pytest.ini

@@ -0,0 +1,3 @@
+[pytest]
+testpaths =
+    bindings/python/examples