Function hover_listener 

pub fn hover_listener(
    fade: Fade,
) -> impl Fn(&bool, &mut Window, &mut App) + 'static

An .on_hover listener driving the fade — pair with hover_t or hover_blend reads of the same Fade in the same element.

The view comes in on the Fade rather than being resolved here: this runs in event-dispatch context, where Window::current_view() asserts.