1 files changed, 75 insertions, 0 deletions
diff --git a/devtools/client/inspector/animation/current-time-timer.js b/devtools/client/inspector/animation/current-time-timer.js
new file mode 100644
index 0000000000..4c08eb09ad
--- /dev/null
+++ b/devtools/client/inspector/animation/current-time-timer.js
@@ -0,0 +1,75 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+/**
+ * In animation inspector, the scrubber and the progress bar moves along the current time
+ * of animation. However, the processing which sync with actual animations is heavy since
+ * we have to communication by the actor. The role of this class is to make the pseudo
+ * current time in animation inspector to proceed.
+ */
+class CurrentTimeTimer {
+  /**
+   * Constructor.
+   *
+   * @param {Object} timeScale
+   * @param {Bool} shouldStopAfterEndTime
+   *               If need to stop the timer after animation end time, set true.
+   * @param {window} win
+   *                 Be used for requestAnimationFrame and performance.
+   * @param {Function} onUpdated
+   *                   Listener function to get updating.
+   *                   This function is called with 2 parameters.
+   *                   1st: current time
+   *                   2nd: if shouldStopAfterEndTime is true and
+   *                        the current time is over the end time, true is given.
+   */
+  constructor(timeScale, shouldStopAfterEndTime, win, onUpdated) {
+    this.baseCurrentTime = timeScale.getCurrentTime();
+    this.endTime = timeScale.getDuration();
+    this.timerStartTime = win.performance.now();
+
+    this.shouldStopAfterEndTime = shouldStopAfterEndTime;
+    this.onUpdated = onUpdated;
+    this.win = win;
+    this.next = this.next.bind(this);
+  }
+
+  destroy() {
+    this.stop();
+    this.onUpdated = null;
+    this.win = null;
+  }
+
+  /**
+   * Proceed the pseudo current time.
+   */
+  next() {
+    if (this.doStop) {
+      return;
+    }
+
+    const currentTime =
+      this.baseCurrentTime + this.win.performance.now() - this.timerStartTime;
+
+    if (this.endTime < currentTime && this.shouldStopAfterEndTime) {
+      this.onUpdated(this.endTime, true);
+      return;
+    }
+
+    this.onUpdated(currentTime);
+    this.win.requestAnimationFrame(this.next);
+  }
+
+  start() {
+    this.next();
+  }
+
+  stop() {
+    this.doStop = true;
+  }
+}
+
+module.exports = CurrentTimeTimer;