Blur

Blur — a wrapper widget that applies a Gaussian-equivalent blur to its child subtree, driven by a Prop<f32> radius (in logical pixels).

Built on BuildContext::set_blur, a per-node paint scope parallel to set_opacity and set_transform. The framework's render walker emits BeginBlurredSubtree { bounds, radius } before this widget's paint and EndBlurredSubtree afterwards; the renderer redirects drawing into an intermediate texture, runs a dual-Kawase blur chain at the requested radius, and composites the blurred result back into the parent pass.

Sub-perceptual radii (< 0.5 px) skip the Begin/End pair entirely so animated 0 → target_radius enable patterns have zero per-frame cost when fully off.

// Static frosted-glass backdrop:
ctx.add(Blur::new(15.0).child(modal_backdrop));

// Click-to-reveal sensitive content:
let visible = ctx.signal(false);
let radius = visible.map(|&v| if v { 0.0 } else { 12.0 });
ctx.add(Blur::new(radius).child(secret_text));

// Animated frosted-glass on modal show:
let radius = ctx.animated_signal(0.0_f32);
ctx.animate().normal().standard().to_or_snap(&radius, 15.0);
ctx.add(Blur::new(radius).child(content));

Layout semantics

Blur does not change layout. The wrapped child reports its full natural size at all blur radii; only the visual paint output is affected.

Performance

Blur is the most expensive paint scope in the framework — every enabled blur scope drives N+M+1 small render passes per frame (N downsamples, M upsamples, +1 composite). Don't put it on widgets that animate every frame at full radius. For "fade-blur on reveal" patterns, animate the radius up to a static value and leave it there. See docs/animation.md §5.8.

Builder methods at a glance

child, child_id

API reference

📖 Full rustdoc API for this module

pub struct Blur

Wraps a child and applies a Gaussian-equivalent blur to the entire subtree, driven by an external Prop<f32> radius (logical pixels).

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

Methods

pub fn new(radius: impl Into<Prop<f32>>) -> Self

Build a blur wrapper bound to radius (in logical pixels). Accepts any Prop<f32> source — f32, Signal<f32>, or Prop<f32>. Sub-perceptual radii (< 0.5) are a no-op.

pub fn child(mut self, widget: impl Widget + 'static) -> Self

Inline child widget (deferred insertion).

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

Pre-registered child by WidgetId.