get_active_region_info Subroutine

    subroutine get_active_region_info(self, unique_ids, ierr)
        ! --- 引数 ---
        implicit none
        class(Type_VTK), intent(in) :: self !! VTK data
        integer(int32), allocatable, intent(inout) :: unique_ids(:)
        integer(int32), intent(out) :: ierr

        ! --- ローカル変数 ---
        integer(int32) :: max_dim
        integer(int32), allocatable :: collected_ids(:)
        integer(int32) :: i_cell, count
        logical(4) :: is_max_dim_element

        max_dim = 0
        ierr = 0

        ! --- ステップ1: メッシュ内の最大次元を判定 ---
        do i_cell = 1, self%num_total_cells
            select case (self%CELLS(i_cell)%cell_type)
            case (VTK_TETRA, VTK_HEXAHEDRON, &
                  VTK_WEDGE, VTK_PYRAMID, &
                  VTK_QUADRATIC_TETRA, VTK_QUADRATIC_HEXAHEDRON)
                max_dim = 3
                exit ! 3Dが見つかったら、それ以上探す必要はない
            case (VTK_TRIANGLE, VTK_PIXEL, &
                  VTK_QUAD, VTK_QUADRATIC_TRIANGLE, &
                  VTK_QUADRATIC_QUAD)
                max_dim = max(max_dim, 2)
            case (VTK_LINE, VTK_QUADRATIC_EDGE)
                max_dim = max(max_dim, 1)
            end select
        end do

        if (max_dim == 0) then
            ierr = -1
            return ! アクティブな要素がない
        end if

        ! --- ステップ2: 最大次元を持つ要素から、すべてのCellEntityIdを収集 ---
        allocate (collected_ids(self%num_total_cells))
        count = 0
        do i_cell = 1, self%num_total_cells
            is_max_dim_element = .false.
            select case (self%CELLS(i_cell)%cell_type)
            case (VTK_TETRA, VTK_HEXAHEDRON, &
                  VTK_WEDGE, VTK_PYRAMID, &
                  VTK_QUADRATIC_TETRA, VTK_QUADRATIC_HEXAHEDRON)
                if (max_dim == 3) is_max_dim_element = .true.
            case (VTK_TRIANGLE, VTK_PIXEL, &
                  VTK_QUAD, VTK_QUADRATIC_TRIANGLE, &
                  VTK_QUADRATIC_QUAD)
                if (max_dim == 2) is_max_dim_element = .true.
            case (VTK_LINE, VTK_QUADRATIC_EDGE)
                if (max_dim == 1) is_max_dim_element = .true.
            end select

            if (is_max_dim_element) then
                count = count + 1
                collected_ids(count) = self%CELLS(i_cell)%cell_entity_id
            end if
        end do

        ! --- ステップ3: 収集したIDリストから、ユニークなものだけを抽出 ---
        ! (これはFortranの標準的なユニーク化のアルゴリズム)
        if (count > 0) then
            call unique(collected_ids(1:count), unique_ids)
        else
            allocate (unique_ids(0))
        end if

    end subroutine get_active_region_info