make_axes Subroutine

    subroutine make_axes(self)
        class(CoordinateAxes), intent(inout) :: self
        real(wp), allocatable :: lines(:,:), major(:,:), minor(:,:)
        real(wp) :: e(3), mark, f
        type(c_ptr) :: group
        integer :: k, i
        if (.not. c_associated(self%nodes%contents)) return
        allocate(lines(3, 0), major(3, 0), minor(3, 0))
        do k = 1, 3
            if (iand(self%drawn, 2**(k-1)) == 0) cycle
            e = 0.0_wp
            e(k) = 1.0_wp
            call append(lines, reshape([0.0_wp, 0.0_wp, 0.0_wp, self%length_ * e], [3, 2]))
            if (self%major > 0.0_wp) then
                do i = 1, int(self%length_ / self%major + 1.0e-9_wp)
                    call append(major, reshape(i * self%major * e, [3, 1]))
                end do
            end if
            if (self%minor > 0.0_wp) then
                do i = 1, int(self%length_ / self%minor + 1.0e-9_wp)
                    mark = i * self%minor
                    if (self%major > 0.0_wp) then                   ! not where a major tick is
                        f = mark / self%major
                        if (abs(f - nint(f)) < 1.0e-6_wp) cycle
                    end if
                    call append(minor, reshape(mark * e, [3, 1]))
                end do
            end if
        end do
        group = vkf_switch_create()
        call add(group, line_node(lines, self%color(), self%width_, .true.))
        call add(group, marker_node(major, self%color(), self%major_size, self%shape_, self%length_, self%image))
        call add(group, marker_node(minor, self%color(), self%minor_size, self%shape_, self%length_, self%image))
        call self%nodes%replace(group)
    end subroutine make_axes