Function can_place 

pub fn can_place(
    cells: &Cells,
    terrain: &HeightGrid<'_>,
    rules: &PlacementRules,
    rect: Rect,
    degrees: i32,
    owner_ok: impl Fn(usize) -> bool,
) -> bool

Whether a building can be placed: every cell of its footprint admits it. This is the test the placement tool makes.

Original: FUN_1400a2a50.