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deferring-state-reads

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Use this skill to push frequently-changing Jetpack Compose state reads (scroll position, animation values, drag offsets) out of the Composition phase and down into Layout or Draw using lambda-based modifiers like Modifier.offset { }, Modifier.layout { }, Modifier.graphicsLayer { }, Modifier.drawBehind { }, and Modifier.drawWithCache { }. Covers the three-phase model (Composition, Layout, Draw), why a state read at phase N invalidates phase N and every phase below, the modifier-phase cheat sheet, and lambda providers (() -> T) for hoisting hot values across composables. Use when the developer mentions every-frame work, scroll jank, animation jank, dropped frames, animated alpha or offset, "the whole subtree recomposes on scroll", Modifier.alpha(state.value), Modifier.offset(x.dp), or graphicsLayer.

recomposition/deferring-state-reads/SKILL.md

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Jun 16, 2026
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Apache-2.0

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# Deferring State Reads — Move Hot Reads from Composition to Draw

Compose runs three phases per frame — **Composition → Layout → Draw**. A state read at phase N invalidates phase N and every phase below it. The single biggest perf win in any animation- or scroll-driven UI is moving a state read from Composition down to Layout or Draw via a lambda-based modifier. This skill teaches Claude how to spot the wrong-phase read and migrate it.

## When to use this skill

- An animation triggers full subtree recomposition on every frame (`Modifier.alpha(progress.value)`, `Modifier.offset(x.dp)`, `Modifier.padding(state.dp)` — `padding` has no lambda overload, so use `Modifier.layout { ... }` or `Modifier.offset { IntOffset(...) }` instead when the inset is animated).
- A scroll position is read directly in a composable body (`val y = scrollState.value`) and the parent recomposes on every pixel of scroll.
- The developer says "every frame", "scroll jank", "animation jank", "dropped frames", or reports the whole screen recomposing on drag.
- A `@TraceRecomposition` log shows the parent's recomposition counter incrementing once per animation tick.
- The developer is passing a hot value (animation progress, scroll offset, drag delta) as a `Float` parameter across composables.

## When NOT to use this skill
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