Function flatten 

pub fn flatten(
    heights: &mut [i16],
    width: usize,
    cells: usize,
    rect: [i32; 4],
) -> bool

Each cell of the inclusive rectangle x0, y0, x1, y1 sets its low corner’s height to 0 (the ground point of the cell’s middle, in the height grid). cells is the map’s cells per side; the height grid is width − 1 cells, the map in its middle.

Original: FUN_1400a35b0.