inertia_tensor.hh

#ifndef VTESTBED_GEOMETRY_INERTIA_TENSOR_HH
#define VTESTBED_GEOMETRY_INERTIA_TENSOR_HH

#include <vtestbed/geometry/types.hh>

namespace vtb {

    namespace geometry {

        template <class T>
        struct Inertia_tensor<T,2> {

            union { T x{}; T xx; };
            union { T y{}; T yy; };
            union { T xy{}; T yx; };

            inline void scale(T factor) { x *= factor, y *= factor, xy *= factor; }

            Rotation_matrix<T,2> matrix() const;

        };

        template <class T>
        struct Inertia_tensor<T,3> {

            union { T x{}; T xx; };
            union { T y{}; T yy; };
            union { T z{}; T zz; };
            union { T yz{}; T zy; };
            union { T xz{}; T zx; };
            union { T xy{}; T yx; };

            inline void
            scale(T factor) {
                x *= factor, y *= factor, z *= factor,
                xy *= factor, xz *= factor, yz *= factor;
            }

            Rotation_matrix<T,3> matrix() const;

        };

        template <class T>
        struct Mass_moments<T,2> {

            Inertia_tensor<T,2> inertia;
            Vertex<T,2> centre{T{}};
            union { T mass{}; T area; };

            inline void
            translate(const Vertex<T,2>& origin) {
                Vertex<T,2> delta = origin - centre;
                inertia.xx += mass*delta(1)*delta(1);
                inertia.yy += mass*delta(0)*delta(0);
                inertia.xy += mass*delta(0)*delta(1);
            }

        };

        template <class T>
        struct Mass_moments<T,3> {
            Inertia_tensor<T,3> inertia;
            Vertex<T,3> centre{T{}};
            union { T mass{}; T volume; };
        };

        template <class T>
        void
        check_matrix(const char* name, const Matrix<T,3>& m, const Matrix<T,3>& im);

    }

}

#endif // vim:filetype=cpp