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_X_POSITION = 2;

[dmazzoni, 2016/12/05 20:07:45]

I'd call it something like ABS_POSITION or MAGNITUDE to clarify that the range
is from -2 to 2

[David Tseng, 2016/12/08 19:05:37]

Sure; done.

+
+/**
  * 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 31 matching lines @@
   }
   var gainNode = this.context_.createGain();
   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.setOrientation(0, 0, 1);
+    panNode.setPosition(pan, 0, 0);
+    panNode.setOrientation(0, -1, 0);

[dmazzoni, 2016/12/05 20:07:45]

Are you sure this is right? Did the original orientation not work? If these are
x, y, z coordinates then 0, 0, 1 would be towards the computer and 0, -1, 0
would be straight up, I think.

[David Tseng, 2016/12/08 19:05:37]

I was fiddling with the audio listener earlier. Reverted this change as it
doesn't seem to matter which direction this points (probably because they're all
fairly close). (I think I was visualizing the 3d plane rotated 90 degrees from
this in the usual Cartesian sense where z goes up/down).

     last.connect(panNode);
     last = panNode;
   }
 
   var reverb = this.masterReverb;
   if (properties.reverb !== undefined) {
     reverb = properties.reverb;
   }
   if (reverb) {
     if (!this.reverbConvolver_) {
@@ skipping 481 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 left = (rect.left + rect.width / 2) / container.width;

[dmazzoni, 2016/12/05 20:07:45]

Maybe just x? It's really the midpoint of the rect, not the left

[David Tseng, 2016/12/08 19:05:37]

Done.

+
+  // Clamp.
+  left = left > 1.0 ? 1.0 : left;

[dmazzoni, 2016/12/05 20:07:45]

x = Math.max(Math.min(x, 1.0), 0.0) or something like that?

[David Tseng, 2016/12/08 19:05:37]

Done.

+  left = left < 0 ? 0 : left;
+
+  // Map to between the negative maximum pan x position and the positive max x
+  // pan position.
+  left = left * 2 * EarconEngine.MAX_PAN_X_POSITION -

[dmazzoni, 2016/12/05 20:07:45]

x = (2 * x - 1) * EarconEngine.MAX_PAN_X_POSITION

[David Tseng, 2016/12/08 19:05:37]

Done.

+      EarconEngine.MAX_PAN_X_POSITION;
+
+  this.masterPan = left;
+};