Copy files

src/helper/delta-time-calculator.ts

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+export class DeltaTimeCalculator {
+  private previousTime: DOMHighResTimeStamp | null = null;
+
+  constructor() {
+    document.addEventListener('visibilitychange', this.handleVisibilityChange.bind(this));
+  }
+
+  public getNextDeltaTime(currentTime: DOMHighResTimeStamp): DOMHighResTimeStamp {
+    if (this.previousTime === null) {
+      this.previousTime = currentTime;
+    }
+
+    const delta = currentTime - this.previousTime;
+    this.previousTime = currentTime;
+    return delta;
+  }
+
+  private handleVisibilityChange() {
+    if (!document.hidden) {
+      this.previousTime = null;
+    }
+  }
+}