Function frame_clock 

pub fn frame_clock(tick: impl FnMut(Duration) + 'static) -> AnyPiece

A frame clock (§8.4): an invisible, zero-size piece that calls tick every animation frame with the wall-clock delta since the previous frame, for as long as it is mounted. Drop it into the tree (e.g. behind a canvas in a zstack) to drive a game loop or self-driven animation: the tick mutates state Signals, and a canvas reading them re-records that frame.

Backend-executed vsync: Day re-arms the platform’s display link only while a frame_clock (or other consumer) is live and stops when the last one unmounts — no idle wakeups. The delta is clamped (≤100 ms) so a backgrounded window can’t deliver a huge jump.

zstack((
    canvas(move |d, sz| draw(d, sz, state)).grow(),
    frame_clock(move |dt| step(dt, state)),
))