Function egui::containers::popup::find_tooltip_position

fn find_tooltip_position(
    screen_rect: Rect,
    widget_rect: Rect,
    allow_placing_below: bool,
    tooltip_size: Vec2,
) -> (Align2, Pos2)

Returns (PIVOT, POS) to mean: put the PIVOT corner of the tooltip at POS.

Note: the position might need to be constrained to the screen, (e.g. moved sideways if shown under the widget) but the Area will take care of that.