1 files changed, 99 insertions, 0 deletions
diff --git a/devtools/server/performance/framerate.js b/devtools/server/performance/framerate.js
new file mode 100644
index 000000000..24f8a7a6b
--- /dev/null
+++ b/devtools/server/performance/framerate.js
@@ -0,0 +1,99 @@
+/* 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";
+
+const { on, once, off, emit } = require("sdk/event/core");
+const { Class } = require("sdk/core/heritage");
+
+/**
+ * A very simple utility for monitoring framerate. Takes a `tabActor`
+ * and monitors framerate over time. The actor wrapper around this
+ * can be found at devtools/server/actors/framerate.js
+ */
+var Framerate = exports.Framerate = Class({
+  initialize: function (tabActor) {
+    this.tabActor = tabActor;
+    this._contentWin = tabActor.window;
+    this._onRefreshDriverTick = this._onRefreshDriverTick.bind(this);
+    this._onGlobalCreated = this._onGlobalCreated.bind(this);
+    on(this.tabActor, "window-ready", this._onGlobalCreated);
+  },
+  destroy: function (conn) {
+    off(this.tabActor, "window-ready", this._onGlobalCreated);
+    this.stopRecording();
+  },
+
+  /**
+   * Starts monitoring framerate, storing the frames per second.
+   */
+  startRecording: function () {
+    if (this._recording) {
+      return;
+    }
+    this._recording = true;
+    this._ticks = [];
+    this._startTime = this.tabActor.docShell.now();
+    this._rafID = this._contentWin.requestAnimationFrame(this._onRefreshDriverTick);
+  },
+
+  /**
+   * Stops monitoring framerate, returning the recorded values.
+   */
+  stopRecording: function (beginAt = 0, endAt = Number.MAX_SAFE_INTEGER) {
+    if (!this._recording) {
+      return [];
+    }
+    let ticks = this.getPendingTicks(beginAt, endAt);
+    this.cancelRecording();
+    return ticks;
+  },
+
+  /**
+   * Stops monitoring framerate, without returning the recorded values.
+   */
+  cancelRecording: function () {
+    this._contentWin.cancelAnimationFrame(this._rafID);
+    this._recording = false;
+    this._ticks = null;
+    this._rafID = -1;
+  },
+
+  /**
+   * Returns whether this instance is currently recording.
+   */
+  isRecording: function () {
+    return !!this._recording;
+  },
+
+  /**
+   * Gets the refresh driver ticks recorded so far.
+   */
+  getPendingTicks: function (beginAt = 0, endAt = Number.MAX_SAFE_INTEGER) {
+    if (!this._ticks) {
+      return [];
+    }
+    return this._ticks.filter(e => e >= beginAt && e <= endAt);
+  },
+
+  /**
+   * Function invoked along with the refresh driver.
+   */
+  _onRefreshDriverTick: function () {
+    if (!this._recording) {
+      return;
+    }
+    this._rafID = this._contentWin.requestAnimationFrame(this._onRefreshDriverTick);
+    this._ticks.push(this.tabActor.docShell.now() - this._startTime);
+  },
+
+  /**
+   * When the content window for the tab actor is created.
+   */
+  _onGlobalCreated: function (win) {
+    if (this._recording) {
+      this._contentWin.cancelAnimationFrame(this._rafID);
+      this._rafID = this._contentWin.requestAnimationFrame(this._onRefreshDriverTick);
+    }
+  }
+});