Proximity

Purpose

Shares one pointer subscription across a set of items and gives each a springed 0–1 closeness value.

Use it when

Several sibling elements need to react to pointer distance — a dock, a magnified row, a set of reactive chips.

API shape

<Proximity distance axis> wraps the set; each item calls useProximityItem() to get a ref and its own proximity motion value.

Judgment

Use axis="x" for horizontal rows: measuring diagonal distance in a dock makes items react as the pointer moves *away* vertically, which feels wrong.

Anything you drive from proximity should degrade to a sensible resting state, because it will be at rest for touch users and reduced-motion users permanently.

Performance

This primitive exists for performance. The naive approach — a listener, a rect cache and a frame callback per item — is how docks become the slowest thing on a page. Here a ten-item dock costs the same as a one-item dock, and rects are re-measured only when layout can actually have changed.