Function reveal_progress 

pub fn reveal_progress(
    id: impl Into<ElementId>,
    delay: Duration,
    window: &mut Window,
    cx: &mut App,
) -> f32

Progress of a one-shot reveal keyed by id, from 0.0 (just mounted) to 1.0 (settled), starting the clock the first time the element renders.

The start instant lives in keyed element state, so a row that keeps its stable identity across renders plays the reveal only once; it requests animation frames until it settles and returns 1.0 immediately under reduced motion.