Function wrap_cell 

pub fn wrap_cell(
    i: usize,
    n: usize,
    ncol: usize,
    vertical: bool,
    as_table: bool,
) -> (usize, usize)

(row, col) of the i-th of n wrap panels in an ncol-column grid: filled row by row (vertical = false, ggplot2’s dir = "h") or column by column (dir = "v"), top to bottom unless as_table = false (ggplot2’s as.table), which puts the first row at the bottom (#412).