use face normals to compute direction for vec2

OpenMesh/OMPropertyVisualizerVector2T_impl.hh

@@ -405,7 +405,7 @@ void OMPropertyVisualizerVector2<MeshT, VectorType>::visualizeHalfedgePropAsStro
 
       typename MeshT::Point v1 = OMPropertyVisualizer<MeshT>::mesh->point(vh0) + 0.5 * (OMPropertyVisualizer<MeshT>::mesh->point(vh1) - OMPropertyVisualizer<MeshT>::mesh->point(vh0));
       VectorType v  = OMPropertyVisualizer<MeshT>::mesh->property(prop, *he_it);
-      ACG::Vec3d normal = OMPropertyVisualizer<MeshT>::mesh->normal(*he_it);
+      ACG::Vec3d normal = OMPropertyVisualizer<MeshT>::mesh->normal(OMPropertyVisualizer<MeshT>::mesh->face_handle(*he_it));
 
       if (vectorWidget->normalize->isChecked() && v.sqrnorm() > 1e-12)
         v.normalize();