Function draw_cursor 

pub fn draw_cursor(
    buf: &mut GlyphBuffer,
    ink: CursorInk,
    cursor: &CursorView,
    layout: &Layout,
    (x, y): (i32, i32),
)

Draws cursor in its style on the tile whose left cell is (x, y), clipped to the tiles of layout.

Corner marks are 1 px Over overlays that stay clear of every letter (game ADR-0024): their vertical arms sit in the pixel column just left of the tile and in the tile’s last pixel column, which the font never inks; their horizontal arms sit on the tile’s top row and on the row just above the tile’s foot (CursorInk::foot_px), outside the letters’ rows. So a neighbour’s letters always show.