Function clear_of_corners 

pub fn clear_of_corners(
    track: Rect,
    vertical: bool,
    surface: Option<&SurfaceShape>,
) -> Rect

track, a bar’s track, with its ends kept out of the rounded corners of surface (in the same coordinates). A vertical track that runs along a side with a rounded corner stops that corner’s radius short of the top or bottom edge; a horizontal track along the bottom or top stops a corner’s radius short of the side. A square corner, a track away from the corners, or no surface leaves it as it is, running to the edge.