Function scroll_to 

pub fn scroll_to(
    index: usize,
    count: usize,
    area: Rect,
    settings: Settings,
    offset: f64,
) -> f64

How far the viewport must move to bring a column fully into view.

Returns the new offset. A column already on screen does not move the view: scrolling something into sight that is already in sight is the kind of motion that makes a layout feel twitchy.