segment_update Subroutine

    subroutine segment_update(self, t)
        class(SegmentArtist), intent(inout) :: self
        real(wp), intent(in) :: t                           !! the current time
        integer :: m, s1, s2, i1, i2
        logical :: changed, redraw
        if (.not. self%chain%is_built()) return
        m = segment_count(self)

        changed = data_changed(self, redraw)
        if (redraw .or. .not. associated(self%traj)) self%n_written = 0
        if (changed) then
            s1 = max(1, min(self%n_written, m))          ! from the last segment written (set_optional)
            call self%chain%reserve(2 * m)
            if (m >= s1) call write_segments(self, s1, m)
            self%n_written = m
        end if

        self%n_drawn = self%n_written
        self%first_drawn_ = 1
        if (self%trace .and. associated(self%traj)) then  ! the segments at the points passed (times up to t)
            call trace_range(self%traj, t, self%traj%num_times(), i1, i2)
            s1 = (i1 - 1 + self%stride_ - 1) / self%stride_ + 1
            s2 = 0
            if (i2 >= 1) s2 = min(self%n_written, (i2 - 1) / self%stride_ + 1)
            self%first_drawn_ = s1
            self%n_drawn = max(0, s2 - s1 + 1)
        end if
        call self%chain%draw_range(2 * self%first_drawn_ - 1, 2 * (self%first_drawn_ + self%n_drawn - 1))
    end subroutine segment_update