10 posts
Layout Inspector renders the composition as an inspectable tree with per-composable recomposition and skip counts. Knowing what it can and cannot tell you is the difference between a diagnosis and a guess.
Layout Inspector, the compiler reports, Macrobenchmark and the system trace each answer a different question. Using the wrong one produces confident, wrong conclusions, and knowing the split is most of performance work.
Reading a state value later — in a lambda rather than as a parameter — moves the invalidation from composition to layout or draw. It is the single highest-leverage Compose optimisation, and it has one shape.
Baseline Profiles ship a list of hot methods so ART compiles them at install time instead of interpreting them on first run. They typically cut startup and first-scroll jank by 20-30% and are unrelated to Compose recomposition.
Strong skipping lets composables skip even with unstable parameters, using instance comparison, and memoises lambdas automatically. It removes most of the need for @Immutable annotations and changes what the compiler report means.
Compose infers stability per class and per parameter, and can emit a report saying what it concluded. Understanding the inference rules — and why List is unstable — explains most unnecessary recomposition.
Compose performance work reduces to knowing which of composition, layout and draw is being invalidated, and why. The diagnostic order matters more than any individual optimisation.
A bitmap costs width × height × 4 bytes in memory regardless of its file size. Decoding at display size, choosing the right config and budgeting the cache are what keep an image-heavy app from being reclaimed.
Compose renders in three phases. Where you read state decides which phase invalidates, and moving a read from composition into layout or draw is the single highest-leverage performance change available.
Compose does not re-run your whole screen when state changes. It re-runs the smallest restartable scopes that read the changed value. Once you can see those scopes, recomposition stops being mysterious.
