Struct WindowMetricsPublisher 

pub struct WindowMetricsPublisher { /* private fields */ }

Per-shell-instance change detector over the window’s WindowMetrics: each of the three shells owns one and drives it from its own resize/insets entry points, publishing only what it reports as changed.

Why this is not a per-frame push

Delivering WindowMetrics to app code means provide_context-ing it under the reactive root owner, exactly as Theme and WindowInsets already are — a plain map insert that notifies nothing and creates no subscription, so re-providing does not itself wake a frame. The guard here exists for cost at the FFI boundary instead: a shell that re-provided metrics unconditionally once per frame would pay a lock write plus an allocation every frame for no observable benefit, since the next rebuild (already driven by the resize or inset change itself) is what actually picks the new value up. This type makes the guarded path the only path: poll returns Some only on an actual change, mirroring ThemeOverrideWatcher’s poll-returns-Option shape and RenderRoot::set_insets’s PartialEq-guarded no-op.

It is deliberately reactive-free (this crate ships no reactive dependency — see docs/ARCHITECTURE.md’s Layer Dependencies): it decides whether to publish and computes what to publish, and each shell owns the provide_context call itself. That keeps the unit conversion and the change-detection host-testable even though both mobile app modules are target-gated and never host-compiled.

Implementations

impl WindowMetricsPublisher

pub fn new() -> Self

A fresh publisher that has published nothing yet.

pub fn poll( &mut self, physical: (u32, u32), scale: f64, insets: WindowInsets, ) -> Option<WindowMetrics>

Assemble the current WindowMetrics (see window_metrics for the unit contract) and return it only if it differs from the last one this publisher reported; None means the shell must not re-provide.

A shell calls this from every point where one of the inputs actually moves — surface create/resize and the insets callback — never from its per-frame driver, which only reads values these entry points already stored.

pub fn last(&self) -> Option<WindowMetrics>

The metrics last published, or None before the first change-reporting poll.

Trait Implementations

impl Debug for WindowMetricsPublisher

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for WindowMetricsPublisher

fn default() -> Self

Returns the “default value” for a type.