Implement support for gmsh files with parametric nodes (#29)

* feat: Add support for importing parametric coordinates from Gmsh 4.1 mesh files.

* refactor: Extract common Gmsh node parsing and element node permutation logic into helper functions.

* minor: fix styling

* minor: handle clippy error

---------

Co-authored-by: Matthew Scroggs <matthew.w.scroggs@gmail.com>

Author: ankurmagdum

ndgrid/src/grid/local_grid/mixed/builder.rs

@@ -37,6 +37,7 @@ pub struct MixedGridBuilder<T: Scalar> {
     cell_ids_to_indices: HashMap<usize, usize>,
     point_indices: HashSet<usize>,
     cell_indices: HashSet<usize>,
+    parametric_coords: HashMap<usize, (usize, Vec<T>)>,
 }
 
 impl<T: Scalar> MixedGridBuilder<T> {
@@ -59,6 +60,7 @@ impl<T: Scalar> MixedGridBuilder<T> {
             cell_ids_to_indices: HashMap::new(),
             point_indices: HashSet::new(),
             cell_indices: HashSet::new(),
+            parametric_coords: HashMap::new(),
         }
     }
 }
@@ -207,6 +209,19 @@ impl<T: Scalar> Builder for MixedGridBuilder<T> {
     fn npts(&self, cell_type: Self::EntityDescriptor, degree: usize) -> usize {
         self.points_per_cell[self.element_indices[&(cell_type, degree)]]
     }
+
+    fn add_point_parametric_coords(&mut self, id: usize, entity_dim: usize, coords: &[T]) {
+        if let Some(&index) = self.point_ids_to_indices.get(&id) {
+            self.parametric_coords
+                .insert(index, (entity_dim, coords.to_vec()));
+        }
+    }
+
+    fn point_parametric_coords(&self, index: usize) -> Option<(usize, &[T])> {
+        self.parametric_coords
+            .get(&index)
+            .map(|(dim, coords)| (*dim, coords.as_slice()))
+    }
 }
 
 impl<T: Scalar> GeometryBuilder for MixedGridBuilder<T> {

ndgrid/src/grid/local_grid/single_element/builder.rs

@@ -54,6 +54,7 @@ pub struct SingleElementGridBuilder<T: Scalar> {
     cell_ids_to_indices: HashMap<usize, usize>,
     point_indices: HashSet<usize>,
     cell_indices: HashSet<usize>,
+    parametric_coords: HashMap<usize, (usize, Vec<T>)>,
 }
 
 impl<T: Scalar> SingleElementGridBuilder<T> {
@@ -84,6 +85,7 @@ impl<T: Scalar> SingleElementGridBuilder<T> {
             cell_ids_to_indices: HashMap::new(),
             point_indices: HashSet::new(),
             cell_indices: HashSet::new(),
+            parametric_coords: HashMap::new(),
         }
     }
 }
@@ -214,6 +216,19 @@ impl<T: Scalar> Builder for SingleElementGridBuilder<T> {
     fn npts(&self, _cell_type: Self::EntityDescriptor, _degree: usize) -> usize {
         self.points_per_cell
     }
+
+    fn add_point_parametric_coords(&mut self, id: usize, entity_dim: usize, coords: &[T]) {
+        if let Some(&index) = self.point_ids_to_indices.get(&id) {
+            self.parametric_coords
+                .insert(index, (entity_dim, coords.to_vec()));
+        }
+    }
+
+    fn point_parametric_coords(&self, index: usize) -> Option<(usize, &[T])> {
+        self.parametric_coords
+            .get(&index)
+            .map(|(dim, coords)| (*dim, coords.as_slice()))
+    }
 }
 
 impl<T: Scalar> GeometryBuilder for SingleElementGridBuilder<T> {