Function animateViewport

ui/src/components/pixi/viewport.ts:103–136

(
  from: Viewport,
  to: Viewport,
  durationMs: number,
  onFrame: (vp: Viewport) => void,
  onComplete?: () => void,
)

/** Smoothly animate from one viewport to another. Returns a cancel function. */
export function animateViewport(
  from: Viewport,
  to: Viewport,
  durationMs: number,
  onFrame: (vp: Viewport) => void,
  onComplete?: () => void,
): () => void {
  const startTime = performance.now();
  let cancelled = false;

  function step() {
    if (cancelled) return;
    const elapsed = performance.now() - startTime;
    const t = Math.min(elapsed / durationMs, 1);
    // Ease-out cubic
    const ease = 1 - Math.pow(1 - t, 3);
    const vp: Viewport = {
      x: from.x + (to.x - from.x) * ease,
      y: from.y + (to.y - from.y) * ease,
      scale: from.scale + (to.scale - from.scale) * ease,
    };
    onFrame(vp);
    if (t < 1) {
      requestAnimationFrame(step);
    } else {
      onComplete?.();
    }
  }

  requestAnimationFrame(step);
  return () => {
    cancelled = true;
  };
}