make_plane Subroutine

    subroutine make_plane(self)
        type(RadialPlane), intent(inout) :: self
        integer, parameter :: n = 360                          ! points around a circle (1 degree)
        real(wp) :: disk(3, n + 1), circle(3, n), a, r
        integer :: idx(3, n), i, k
        real(wp), allocatable :: lines(:,:), main(:,:)
        type(c_ptr) :: group
        if (.not. c_associated(self%nodes%contents)) return
        ! the disk: a fan around the center
        disk(:, n + 1) = 0.0_wp
        do i = 1, n
            a = 2.0_wp * pi * (i - 1) / n
            disk(:, i) = self%radius_ * [cos(a), sin(a), 0.0_wp]
            idx(:, i) = [n + 1, i, modulo(i, n) + 1]
        end do
        allocate(lines(3, 0), main(3, 0))
        ! circles: the edge, and every radial_spacing from the center
        if (self%radial_spacing > 0.0_wp) then
            call append(lines, closed_segments(disk(:, 1:n)))
            k = 1
            do while (k * self%radial_spacing < self%radius_ * (1.0_wp - 1.0e-6_wp))
                r = k * self%radial_spacing
                circle = r / self%radius_ * disk(:, 1:n)
                call append(lines, closed_segments(circle))
                k = k + 1
            end do
        end if
        ! radial lines: along +x (thicker), then every lon_spacing
        if (self%lon_spacing > 0.0_wp) then
            k = 0
            do while (k * self%lon_spacing < 2.0_wp * pi - 1.0e-6_wp)
                a = k * self%lon_spacing
                if (k == 0) then
                    call append(main, reshape([0.0_wp, 0.0_wp, 0.0_wp, self%radius_ * [cos(a), sin(a), 0.0_wp]], [3, 2]))
                else
                    call append(lines, reshape([0.0_wp, 0.0_wp, 0.0_wp, self%radius_ * [cos(a), sin(a), 0.0_wp]], [3, 2]))
                end if
                k = k + 1
            end do
        end if
        group = vkf_switch_create()
        call add(group, surface_node(disk, idx, self%plane_color_))
        call add(group, line_node(lines, self%line_color_, 1.0_wp, .true.))
        call add(group, line_node(main, self%line_color_, 3.0_wp, .true.))
        call self%nodes%replace(group)
    end subroutine make_plane