Compose performance is one question asked in four places
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.
compose
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Drag-and-drop crosses app boundaries, which is why it isn't just a drag gesture
Compose's drag-and-drop moves ClipData between sources and targets, including across apps. Reordering a list is a different problem with a different solution, and conflating them is why reorder implementations get complicated.
An animation is state, and that is why it restarts
animate*AsState holds its value in the composition. A key change starts it over.
Your semantics tree is your test API and your accessibility API at once
A testTag is invisible to a screen reader. A contentDescription is not.
Focus is the input model you don't test until someone plugs in a keyboard
Compose's focus system handles keyboard, D-pad and accessibility navigation. The APIs are small, but modifier order matters, and a form with no focus handling is unusable on any device without a touchscreen.
Nested scroll is a negotiation, and there are four moments to intervene
NestedScrollConnection gives parents four chances to consume scroll deltas around a child. Choosing the wrong one is why collapsing headers collapse late, and why same-axis nesting misbehaves.
Pinch, pan and rotate arrive together, and the centroid is what ties them
Multi-touch gestures produce pan, zoom and rotation simultaneously. The centroid — the point between the fingers — is what makes the transform feel anchored, and ignoring it is the most common photo-viewer bug.
Swipe-to-dismiss is a state machine with anchors, not a drag handler
Hand-rolled swipe gestures compare a distance threshold and ignore velocity, which is why a fast flick feels wrong. AnchoredDraggableState models discrete positions and settles between them using both distance and speed.
clickable does six things, and detectTapGestures does one
Modifier.clickable adds accessibility semantics, focus, keyboard activation, ripple and a minimum touch target on top of tap detection. Reaching for detectTapGestures instead silently drops all of it.
Every gesture in Compose is a coroutine reading a stream of events
pointerInput gives you a coroutine scope over raw pointer events. Understanding that gestures are suspending loops rather than callbacks explains the whole API, including why the key parameter matters more than it looks.
Automated checks find the missing labels. They can't tell you the label is wrong.
Compose's accessibility checks catch touch targets, contrast and missing labels automatically. The failures they cannot detect — wrong labels, bad order, gesture-only actions — need a person, and knowing the split makes both cheaper.
Reading order is layout order, until your layout stops matching your meaning
Screen readers traverse in layout order, which breaks when a floating action button, a sticky header or a two-column layout puts visual priority somewhere else. Traversal groups and indices reorder without moving anything.