Support basic stereo pan positioning for earcons

chrome/browser/resources/chromeos/chromevox/cvox2/background/earcon_engine.js

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /**
  * @fileoverview This is the low-level class that generates ChromeVox's
  * earcons. It's designed to be self-contained and not depend on the
  * rest of the code.
  */
 
@@ skipping 139 matching lines @@
  */
 EarconEngine.HALF_STEP = Math.pow(2.0, 1.0 / 12.0);
 
 /**
  * @type {string} The base url for earcon sound resources.
  * @const
  */
 EarconEngine.BASE_URL = chrome.extension.getURL('cvox2/background/earcons/');
 
 /**
+ * The maximum value to pass to PannerNode.setPosition.
+ */
+EarconEngine.MAX_PAN_ABS_X_POSITION = 4;
+
+/**
  * Fetches a sound asynchronously and loads its data into an AudioBuffer.
  *
  * @param {string} name The name of the sound to load.
  * @param {string} url The url where the sound should be fetched from.
  */
 EarconEngine.prototype.loadSound = function(name, url) {
   var request = new XMLHttpRequest();
   request.open('GET', url, true);
   request.responseType = 'arraybuffer';
 
@@ skipping 33 matching lines @@
   gainNode.gain.value = gain;
   var first = gainNode;
   var last = gainNode;
 
   var pan = this.masterPan;
   if (properties.pan !== undefined) {
     pan = properties.pan;
   }
   if (pan != 0) {
     var panNode = this.context_.createPanner();
-    panNode.setPosition(pan, 0, -1);
+    panNode.setPosition(pan, 0, 0);
     panNode.setOrientation(0, 0, 1);
     last.connect(panNode);
     last = panNode;
   }
 
   var reverb = this.masterReverb;
   if (properties.reverb !== undefined) {
     reverb = properties.reverb;
   }
   if (reverb) {
@@ skipping 482 matching lines @@
   }
 
   for (var i = 0; i < this.progressSources_.length; i++) {
     this.progressSources_[i][1].stop();
   }
   this.progressSources_ = [];
 
   window.clearInterval(this.progressIntervalID_);
   this.progressIntervalID_ = null;
 };
+
+/**
+ * @param {chrome.automation.Rect} rect
+ * @param {chrome.automation.Rect} container
+ */
+EarconEngine.prototype.setPositionForRect = function(rect, container) {
+  // The horizontal position computed as a percentage relative to its container.
+  var x = (rect.left + rect.width / 2) / container.width;
+
+  // Clamp.
+  x = Math.min(Math.max(x, 0.0), 1.0);
+
+  // Map to between the negative maximum pan x position and the positive max x
+  // pan position.
+  x = (2 * x - 1) * EarconEngine.MAX_PAN_ABS_X_POSITION;
+
+  this.masterPan = x;
+};