BaseTriangle.h

#pragma once
 
#include <Caribou/config.h>
#include <Caribou/constants.h>
#include <Caribou/Geometry/Element.h>
#include <Eigen/Core>
 
namespace caribou::geometry {
 
template<typename Derived>
struct BaseTriangle : public Element<Derived> {
    // Types
    using Base = Element<Derived>;
 
    using LocalCoordinates = typename Base::LocalCoordinates;
    using WorldCoordinates = typename Base::WorldCoordinates;
 
    using GaussNode = typename Base::GaussNode;
 
    template <UNSIGNED_INTEGER_TYPE Dim>
    using Vector = typename Base::template Vector<Dim>;
 
    template <UNSIGNED_INTEGER_TYPE Rows, UNSIGNED_INTEGER_TYPE Cols>
    using Matrix = typename Base::template Matrix<Rows, Cols>;
 
    // Constants
    static constexpr auto CanonicalDimension = Base::CanonicalDimension;
    static constexpr auto Dimension = Base::Dimension;
    static constexpr auto NumberOfNodesAtCompileTime = Base::NumberOfNodesAtCompileTime;
    static constexpr auto NumberOfGaussNodesAtCompileTime = Base::NumberOfGaussNodesAtCompileTime;
 
    static_assert(Dimension == 2 or Dimension == 3, "Triangles can only be of dimension 2 or 3.");
 
    BaseTriangle() = default;
 
    template<typename EigenType, REQUIRES(EigenType::RowsAtCompileTime == NumberOfNodesAtCompileTime)>
    explicit BaseTriangle(Eigen::EigenBase<EigenType> & nodes) :p_nodes(nodes.derived().template cast<typename Base::Scalar>()) {}
 
    template<typename EigenType, REQUIRES(EigenType::RowsAtCompileTime == NumberOfNodesAtCompileTime)>
    explicit BaseTriangle(const Eigen::EigenBase<EigenType> & nodes) :p_nodes(nodes.derived().template cast<typename Base::Scalar>()) {}
 
    template <
        typename ...Nodes,
        REQUIRES(NumberOfNodesAtCompileTime == sizeof...(Nodes)+1)
    >
    explicit BaseTriangle(const WorldCoordinates & first_node, Nodes&&...remaining_nodes)
    {
        construct_from_nodes<0>(first_node, std::forward<Nodes>(remaining_nodes)...);
    }
 
    // Public methods common to all triangle types
 
    inline auto normal() const noexcept ->  WorldCoordinates {
        static_assert(Dimension == 3, "Can only get the normal of a triangle in a 3D world");
        const WorldCoordinates v1 = self().node(1) - self().node(0);
        const WorldCoordinates v2 = self().node(2) - self().node(0);
 
        return v1.cross(v2).normalized();
    }
 
    inline auto edges() const {
        return self().get_boundary_elements_nodes();
    }
 
private:
    // Implementations
    friend struct Element<Derived>;
    [[nodiscard]]
    inline auto get_number_of_nodes() const {return NumberOfNodesAtCompileTime;}
    inline auto get_number_of_gauss_nodes() const {return NumberOfGaussNodesAtCompileTime;}
    inline auto get_node(const UNSIGNED_INTEGER_TYPE & index) const {return WorldCoordinates(p_nodes.row(index));};
    inline auto get_nodes() const -> const auto & {return p_nodes;};
    inline auto get_center() const {return Base::world_coordinates(LocalCoordinates({1/3., 1/3.}));};
    inline auto get_number_of_boundary_elements() const -> UNSIGNED_INTEGER_TYPE {return 3;};
    inline auto get_contains_local(const LocalCoordinates & xi, const FLOATING_POINT_TYPE & eps) const -> bool {
        const auto & u = xi[0];
        const auto & v = xi[1];
        return (u > -eps) and (v > -eps) and (1 - u - v > -eps);
    }
 
    auto self() -> Derived& { return *static_cast<Derived*>(this); }
    auto self() const -> const Derived& { return *static_cast<const Derived*>(this); }
 
    template <size_t index, typename ...Nodes, REQUIRES(sizeof...(Nodes) >= 1)>
    inline
    void construct_from_nodes(const WorldCoordinates & first_node, Nodes&&...remaining_nodes) {
        p_nodes.row(index) = first_node;
        construct_from_nodes<index+1>(std::forward<Nodes>(remaining_nodes)...);
    }
 
    template <size_t index>
    inline
    void construct_from_nodes(const WorldCoordinates & last_node) {
        p_nodes.row(index) = last_node;
    }
protected:
    Matrix<NumberOfNodesAtCompileTime, Dimension> p_nodes;
};
 
}