Type Alias SurfaceObserver

The §45 autoResize seam: subscribes onResize to the host's surface-size changes and returns the unsubscribe.

A function the host supplies rather than a ResizeObserver this package constructs — the discipline PointerInput uses for PointerSurface and this class already uses for ApplicationOptions.now. four/application compiles with no DOM lib and must run in Node, in a worker, and in a headless test, so it names no DOM type; in a browser the whole adapter is five lines:

const app = new Application({
  canvas,
  renderer: new WebglRenderer(),
  surfaceObserver: (onResize) => {
    const observer = new ResizeObserver(([entry]) => {
      const box = entry.contentRect;
      onResize(box.width, box.height, devicePixelRatio);
    });
    observer.observe(canvas);
    return () => { observer.disconnect(); };
  },
});
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The returned function is called exactly once, by Application.dispose (§83: what the application subscribed, the application unsubscribes). It must be safe to call after the surface itself has gone.