Fade

Fade — a wrapper widget that animates its child between hidden (opacity 0) and visible (opacity 1) when an external Signal<bool> toggles.

Drives an opacity: Signal<f32> ∈ [0, 1] and applies it to its own subtree via BuildContext::set_opacity. The framework's render walker emits SetOpacity(value) before this widget's paint and RestoreOpacity afterwards, so the multiplier composes correctly with ancestor opacity scopes via the canvas's stacked opacity model.

let visible = ctx.signal(false);
ctx.add(Fade::new(visible.clone()).child(tooltip_content));
// ...elsewhere:
visible.set(true);  // fades in over `motion.duration_fast`

Layout semantics

Fade does not change layout. The wrapped child reports its full natural size at all opacity values, so reserving space for a to-be-faded-in widget works the same whether the widget is fully visible or fully hidden.

For overlays where the dismiss should be deferred until the fade-out completes (tooltip / popover / snackbar / dialog), prefer OverlayRequest::with_fade instead — that path coordinates the dismiss with the tween so the overlay survives until the opacity reaches zero.

Reduced motion

Honours prefers-reduced-motion: under reduced motion the opacity snaps to its end value instead of tweening.

Builder methods at a glance

child, child_id

API reference

📖 Full rustdoc API for this module

`pub struct Fade`

Wraps a child and animates the entire subtree's opacity between 0 and 1, driven by an external Signal<bool>.

#![allow(unused)]
fn main() {
pub struct Fade { /* fields */ }
}

Methods

`pub fn new(visible: impl Into<Prop<bool>>) -> Self`

Build a fade wrapper bound to visible. Initially hidden iff visible.get() is false at the first build().

Accepts any Prop<bool> source — Signal<bool>, Prop<bool>, or a plain bool (for static "always visible" / "always hidden" cases without a tween).

Inline child widget (deferred insertion).

`pub fn child_id(mut self, id: WidgetId) -> Self`

Pre-registered child by WidgetId.

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