- added renderer

- Added undo

src/fluency/rendering/occ_to_mesh.py

@@ -87,17 +87,18 @@ def occ_shape_to_ply(
         f"Tessellation: {len(vertices)} vertices, {len(faces)} triangles"
     )
 
-    # Compute outward-facing vertex normals from triangle geometry.
-    # This ensures consistent lighting even when OCC triangulation winding
-    # is inconsistent across faces (e.g. after location transforms).
-    normals = _compute_outward_normals(vertices, faces, shape)
+    # Compute outward-facing vertex normals AND correct face winding.
+    # OCC triangulation produces inconsistent winding across faces (especially
+    # after location transforms). Mitsuba uses face winding for front/back
+    # determination, so both normals AND winding must be consistent.
+    normals, corrected_faces = _compute_outward_normals(vertices, faces, shape)
 
-    # Write PLY with normals
+    # Write PLY with corrected faces and normals
     if output_path is None:
         fd, output_path = tempfile.mkstemp(suffix=".ply", prefix="fluency_render_")
         os.close(fd)
 
-    _write_ply(output_path, vertices, faces, normals)
+    _write_ply(output_path, vertices, corrected_faces, normals)
     logger.info(f"Wrote PLY: {output_path}")
     return output_path
 
@@ -106,14 +107,18 @@ def _compute_outward_normals(
     vertices: np.ndarray,
     faces: np.ndarray,
     shape,
-) -> np.ndarray:
-    """Compute outward-facing vertex normals.
+) -> Tuple[np.ndarray, np.ndarray]:
+    """Compute outward-facing vertex normals and correct face winding.
 
     1. Compute per-face normals from cross product of triangle edges.
     2. Determine correct orientation by checking face normals against the
        shape centroid (outward = away from center).
     3. Flip triangles with inward normals before accumulating to vertices.
     4. Average and normalize per-vertex normals.
+
+    Returns (normals, corrected_faces) so the PLY writer can use consistent
+    winding order — critical for Mitsuba which uses winding for front/back
+    face determination.
     """
     n_verts = len(vertices)
     v_normals = np.zeros((n_verts, 3), dtype=np.float64)
@@ -189,7 +194,7 @@ def _compute_outward_normals(
     v_lengths[v_lengths < 1e-10] = 1.0
     v_normals /= v_lengths
 
-    return v_normals.astype(np.float32)
+    return v_normals.astype(np.float32), corrected_faces.astype(np.uint32)
 
 
 def occ_shape_to_stl(