fix(TetrahedralSolid): adding function to get polyhedron facet triangle (with geometrical points).

Author: benoit2776

include/geode/mesh/core/tetrahedral_solid.hpp

@@ -73,6 +73,9 @@ namespace geode
         [[nodiscard]] PolyhedronFacetsVertices polyhedron_facets_vertices(
             index_t polyhedron ) const final;
 
+        [[nodiscard]] Triangle< dimension > polyhedron_facet_triangle(
+            const PolyhedronFacet facet ) const;
+
         [[nodiscard]] typename SolidMesh< dimension >::VerticesAroundVertex
             vertices_around_vertex( index_t vertex_id ) const final;
 

src/geode/mesh/core/tetrahedral_solid.cpp

@@ -449,6 +449,16 @@ namespace geode
         return result;
     }
 
+    template < index_t dimension >
+    Triangle< dimension >
+        TetrahedralSolid< dimension >::polyhedron_facet_triangle(
+            const PolyhedronFacet facet ) const
+    {
+        const auto vertices = this->polyhedron_facet_vertices( facet );
+        return { this->point( vertices[0] ), this->point( vertices[1] ),
+            this->point( vertices[2] ) };
+    }
+
     template < index_t dimension >
     std::optional< PolyhedronFacet >
         TetrahedralSolid< dimension >::polyhedron_adjacent_facet(