Fix torus mesh parameterization

Author: Asixa

tests/test_geometry_smoke.py

@@ -1,9 +1,11 @@
 from __future__ import annotations
 
+import math
+
 import pytest
 import torch
 
-from witwin.core import Box, Cylinder, Mesh, Sphere
+from witwin.core import Box, Cylinder, Mesh, Sphere, Torus
 
 
 def _grid():
@@ -71,6 +73,26 @@ def test_geometry_construction_to_mesh_and_to_mask(geometry, segments, inside_po
     assert torch.any(occupancy < 0.5)
 
 
+def test_torus_mesh_matches_analytic_extents_and_volume():
+    major_radius = 0.8
+    minor_radius = 0.2
+    torus = Torus(major_radius=major_radius, minor_radius=minor_radius, axis="z")
+    vertices, faces = torus.to_mesh(segments=48)
+
+    expected_extents = torch.tensor(
+        [major_radius + minor_radius, major_radius + minor_radius, minor_radius],
+        dtype=vertices.dtype,
+    )
+    torch.testing.assert_close(vertices.abs().amax(dim=0), expected_extents, rtol=1e-6, atol=1e-6)
+
+    triangles = vertices[faces].to(torch.float64)
+    signed_volume = torch.sum(
+        torch.sum(triangles[:, 0] * torch.cross(triangles[:, 1], triangles[:, 2], dim=1), dim=1)
+    ) / 6.0
+    expected_volume = 2.0 * math.pi**2 * major_radius * minor_radius**2
+    assert abs(float(signed_volume)) == pytest.approx(expected_volume, rel=1e-2)
+
+
 def test_mesh_roundtrip_preserves_world_vertices_and_faces():
     base = Box(position=(0.25, -0.15, 0.4), size=(0.5, 0.3, 0.7))
     vertices, faces = base.to_mesh()

witwin/core/geometry/primitives.py

@@ -427,7 +427,7 @@ def to_mesh(self, segments=16):
             for minor in range(minor_segments):
                 phi = 2 * np.pi * minor / minor_segments
                 vertices.append([
-                    np.cos(phi) * np.cos(theta),
+                    np.cos(phi),
                     np.cos(phi) * np.sin(theta),
                     np.sin(phi),
                     np.cos(theta),