Complete the implementation of up/down-mixing rules for AudioNode

third_party/WebKit/LayoutTests/webaudio/resources/mixing-rules.js

+// Utilities for mixing rule testing.
+// http://webaudio.github.io/web-audio-api/#channel-up-mixing-and-down-mixing
+
+
+/**
+ * Create an n-channel buffer, with all sample data zero except for a shifted
+ * impulse. The impulse position depends on the channel index. For example, for
+ * a 4-channel buffer:
+ *  channel 0: 1 0 0 0 0 0 0 0
+ *  channel 1: 0 1 0 0 0 0 0 0
+ *  channel 2: 0 0 1 0 0 0 0 0
+ *  channel 3: 0 0 0 1 0 0 0 0
+ * @param  {Number} numberOfChannels Number of channels of test buffer.

[Raymond Toy, 2016/03/08 18:04:06]

If you're going to document the code this way, don't you need an entry for
context and frameLength?

[hongchan, 2016/03/08 23:53:34]

Done.

+ * @return {AudioBuffer}
+ */
+function createShiftedImpulseBuffer(context, numberOfChannels, frameLength) {
+    var shiftedImpulseBuffer = context.createBuffer(numberOfChannels, frameLength, context.sampleRate);
+    for (var channel = 0; channel < numberOfChannels; ++channel) {
+      var data = shiftedImpulseBuffer.getChannelData(channel);
+      data[channel] = 1;
+    }
+
+    return shiftedImpulseBuffer;
+}
+
+/**
+ * Stringify AudioBuffer content with options.

[Raymond Toy, 2016/03/08 18:04:07]

Not obvious how you want to stringify the AudioBuffer.  Describe better.

[hongchan, 2016/03/08 23:53:35]

Done.

+ * @param  {AudioBuffer} audioBuffer AudioBuffer object to stringify.

[Raymond Toy, 2016/03/08 18:04:07]

The other parameters/outputs have the description lined up in a column.  Make
this match?

[hongchan, 2016/03/08 23:53:34]

Done.

+ * @param  {Number} frameLength Length to print.
+ * @param  {Number} frameOffset Offset frames to print.

[Raymond Toy, 2016/03/08 18:04:07]

This description of frameOffset doesn't really say anything.  Make it clearer.

[hongchan, 2016/03/08 23:53:34]

Done.

+ * @return {String}             Assembled string for printing.
+ */
+function stringifyBuffer(audioBuffer, frameLength, frameOffset) {
+  frameOffset = (frameOffset || 0);
+
+  var stringifiedBuffer = '';
+  for (var channel = 0; channel < audioBuffer.numberOfChannels; ++channel) {
+    var channelData = audioBuffer.getChannelData(channel);
+    for (var i = 0; i < frameLength; ++i)
+      stringifiedBuffer += channelData[i + frameOffset] + ' ';
+    stringifiedBuffer += '\n';
+  }
+
+  return stringifiedBuffer;
+}
+
+/**
+ * Computer number of channels from the connection.

[Raymond Toy, 2016/03/08 18:04:06]

Typo: "Computer" -> "Compute"

[hongchan, 2016/03/08 23:53:35]

Done.

+ * @param  {String} connections       A string specifies the connection. The
+ *                                    string "128" means 3 connections, having

[Raymond Toy, 2016/03/08 18:04:06]

Description doesn't line up with the rest of the descriptions.

This also means that we can't have more than 9 channels.  Is this a problem?

[hongchan, 2016/03/08 23:53:34]

Done.

+ *                                    1, 2, and 8 channels respectively.
+ * @param  {Number} channelCount     Channel count.
+ * @param  {String} channelCountMode Channel count mode.
+ * @return {Number}                  A computed number of channels.

[Raymond Toy, 2016/03/08 18:04:06]

A link to the spec would be nice. I can never remember the rules and it always
takes me a while to find it in the spec.

[hongchan, 2016/03/08 23:53:35]

URL is at the top of this file, and I don't think here is the place for the
link.

[Raymond Toy, 2016/03/08 23:56:54]

That link is for the mixing rules.  This function is handling the computed
number of channels.  A link to that section would be nice.

[hongchan, 2016/03/09 19:34:24]

It does not have a separate section, but a definition. I added a URL to that.

+ */
+function computeNumberOfChannels(connections, channelCount, channelCountMode) {
+  if (channelCountMode == "explicit")
+    return channelCount;
+
+  // Must have at least one channel.
+  var computedNumberOfChannels = 1;
+
+  // Compute "computedNumberOfChannels" based on all the connections.
+  for (var i = 0; i < connections.length; ++i) {
+    var connectionNumberOfChannels = parseInt(connections[i]);
+    computedNumberOfChannels = Math.max(computedNumberOfChannels, connectionNumberOfChannels);
+  }
+
+  if (channelCountMode == "clamped-max")
+    computedNumberOfChannels = Math.min(computedNumberOfChannels, channelCount);
+
+  return computedNumberOfChannels;
+}
+
+/**
+ * Apply up/down-mixing rules based on 'speaker' interpretation.
+ * @param  {AudioBuffer} source      Source audio buffer.
+ * @param  {AudioBuffer} destination Destination audio buffer.
+ */
+function speakersSum(source, destination) {
+  if (source.length != destination.length)
+    throw "[mixing-rules.js] speakerSum(): buffer lengths mismatch";

[Raymond Toy, 2016/03/08 18:04:06]

Since you know the lengths, print them out in the message, somehow.

[hongchan, 2016/03/08 23:53:35]

Done.

+
+  if (source.numberOfChannels === destination.numberOfChannels) {
+    for (var channel = 0; channel < destination.numberOfChannels; ++channel) {
+      var sourceChannel = source.getChannelData(channel);
+      var destinationChannel = destination.getChannelData(channel);
+      for (var i = 0; i < destinationChannel.length; i++)
+        destinationChannel[i] += sourceChannel[i];
+    }
+
+    return;
+  }
+
+  if (source.numberOfChannels < destination.numberOfChannels)

[Raymond Toy, 2016/03/08 18:04:07]

I find this style confusing.  I think it's clearer just to do

if (s.nc === d.nc) {
 ...
} else if (s.nc < d.nc) {
 ...
} else {
 ...
}

[hongchan, 2016/03/08 23:53:34]

Done.

+    processUpMix(source, destination);
+  else
+    processDownMix(source, destination);
+}
+
+/**
+ * Discrete channel interpretation mixing.
+ * @param  {AudioBuffer} source        Source audio buffer.
+ * @param  {AudioBuffer} destination   Destination audio buffer.

[Raymond Toy, 2016/03/08 18:04:07]

Since nothing is returned, I suggest saying that the destination is modified
with the result.  Otherwise, this looks like a nop.

[hongchan, 2016/03/08 23:53:34]

Done.

+ */
+function discreteSum(source, destination) {
+  if (source.length != destination.length)
+    throw "[mixing-rules.js] discreteSum(): buffer lengths mismatch";

[Raymond Toy, 2016/03/08 18:04:06]

Give lengths in message.

[hongchan, 2016/03/08 23:53:35]

Done.

+
+  var numberOfChannels = source.numberOfChannels < destination.numberOfChannels
+    ? source.numberOfChannels
+    : destination.numberOfChannels;

[Raymond Toy, 2016/03/08 18:04:07]

numberOfChannels = Math.min(source.numberOfChannels,
destination.numberOfChannels)?  Right?

[hongchan, 2016/03/08 23:53:34]

Done. I was following the original test code - but this is better.

+
+  for (var channel = 0; channel < numberOfChannels; ++channel) {
+    var sourceChannel = source.getChannelData(channel);
+    var destinationChannel = destination.getChannelData(channel);
+    for (var i = 0; i < destinationChannel.length; i++)
+      destinationChannel[i] += sourceChannel[i];
+  }
+}
+
+/**
+ * Process up-mix.
+ * @param  {AudioBuffer} source        Source audio buffer.
+ * @param  {AudioBuffer} destination   Destination audio buffer.

[Raymond Toy, 2016/03/08 18:04:07]

Say that the destination is modified.

[hongchan, 2016/03/08 23:53:35]

Done.

+ */
+function processUpMix(source, destination) {
+  var numberOfSourceChannels = source.numberOfChannels;
+  var numberOfDestinationChannels = destination.numberOfChannels;
+  var i, length = destination.length;
+
+  // Up-mixing: 1 -> 2, 1 -> 4
+  //   output.L = input
+  //   output.R = input
+  //   output.SL = 0 (in the case of 1 -> 4)
+  //   output.SR = 0 (in the case of 1 -> 4)

[Raymond Toy, 2016/03/08 18:04:06]

Make comment notation match code notation more closely.  output vs destination,
input vs source.

[hongchan, 2016/03/08 23:53:35]

Done.

+  if ((numberOfSourceChannels === 1 && numberOfDestinationChannels === 2) ||
+      (numberOfSourceChannels === 1 && numberOfDestinationChannels === 4)) {
+    var sourceChannel = source.getChannelData(0);
+    var destinationChannel0 = destination.getChannelData(0);
+    var destinationChannel1 = destination.getChannelData(1);
+    for (i = 0; i < length; i++) {
+      destinationChannel0[i] += sourceChannel[i];

[Raymond Toy, 2016/03/08 18:04:06]

This doesn't match the comment. You're summing the source into the destination,
but the comment says destination = source.

Update the code or update the comment appropriately.

[hongchan, 2016/03/08 23:53:34]

Done.

+      destinationChannel1[i] += sourceChannel[i];
+    }
+
+    return;
+  }
+
+  // Up-mixing: 1 -> 5.1
+  //   output.L = 0
+  //   output.R = 0
+  //   output.C = input
+  //   output.LFE = 0
+  //   output.SL = 0
+  //   output.SR = 0
+  if (numberOfSourceChannels == 1 && numberOfDestinationChannels == 6) {
+    var sourceChannel = source.getChannelData(0);
+    var destinationChannel2 = destination.getChannelData(2);
+    for (i = 0; i < length; i++)
+      destinationChannel2[i] += sourceChannel[i];

[Raymond Toy, 2016/03/08 18:04:06]

Again, this doesn't match the comment.  Update comment or code.

[hongchan, 2016/03/08 23:53:34]

Done.

+
+    return;
+  }
+
+  // Up-mixing: 2 -> 4, 2 -> 5.1
+  //   output.L = input.L
+  //   output.R = input.R
+  //   output.C = 0 (in the case of 2 -> 5.1)
+  //   output.LFE = 0 (in the case of 2 -> 5.1)
+  //   output.SL = 0
+  //   output.SR = 0
+  if ((numberOfSourceChannels === 2 && numberOfDestinationChannels === 4) ||
+      (numberOfSourceChannels === 2 && numberOfDestinationChannels === 6)) {
+    var sourceChannel0 = source.getChannelData(0);
+    var sourceChannel1 = source.getChannelData(1);
+    var destinationChannel0 = destination.getChannelData(0);
+    var destinationChannel1 = destination.getChannelData(1);
+    for (i = 0; i < length; i++) {
+      destinationChannel0[i] += sourceChannel0[i];
+      destinationChannel1[i] += sourceChannel1[i];

[Raymond Toy, 2016/03/08 18:04:07]

Again, this doesn't match the comment.  Update comment or code.

[hongchan, 2016/03/08 23:53:35]

Done.

+    }
+
+    return;
+  }
+
+  // Up-mixing: 4 -> 5.1
+  //   output.L = input.L
+  //   output.R = input.R
+  //   output.C = 0
+  //   output.LFE = 0
+  //   output.SL = input.SL
+  //   output.SR = input.SR
+  if (numberOfSourceChannels === 4 && numberOfDestinationChannels === 6) {
+    var sourceChannel0 = source.getChannelData(0);
+    var sourceChannel1 = source.getChannelData(1);
+    var sourceChannel2 = source.getChannelData(2);
+    var sourceChannel3 = source.getChannelData(3);
+    var destinationChannel0 = destination.getChannelData(0);
+    var destinationChannel1 = destination.getChannelData(1);
+    var destinationChannel4 = destination.getChannelData(4);
+    var destinationChannel5 = destination.getChannelData(5);
+    for (i = 0; i < length; i++) {
+      destinationChannel0[i] += sourceChannel0[i];
+      destinationChannel1[i] += sourceChannel1[i];
+      destinationChannel4[i] += sourceChannel2[i];
+      destinationChannel5[i] += sourceChannel3[i];
+    }
+
+    return;
+  }
+
+  // All other cases, fall back to the discrete sum.
+  discreteSum(source, destination);
+}
+
+/**
+ * Process down-mix from source to destination by summing into the existing data.
+ * @param  {AudioBuffer} source      Source audio buffer.
+ * @param  {AudioBuffer} destination Destination audio buffer.
+ */
+function processDownMix(source, destination) {
+  var numberOfSourceChannels = source.numberOfChannels;
+  var numberOfDestinationChannels = destination.numberOfChannels;
+  var i, length = destination.length;
+
+  // Down-mixing: 2 -> 1
+  //   output = 0.5 * (input.L + input.R)
+  if (numberOfSourceChannels === 2 && numberOfDestinationChannels === 1) {
+    var sourceChannel0 = source.getChannelData(0);
+    var sourceChannel1 = source.getChannelData(1);
+    var destinationChannel0 = destination.getChannelData(0);
+    for (i = 0; i < length; i++)
+      destinationChannel0[i] += 0.5 * (sourceChannel0[i] + sourceChannel1[i]);

[Raymond Toy, 2016/03/08 18:04:07]

Again, this doesn't match the comment.  Update comment or code.

[hongchan, 2016/03/08 23:53:35]

Done.

+
+    return;
+  }
+
+  // Down-mixing: 4 -> 1
+  //   output = 0.25 * (input.L + input.R + input.SL + input.SR)
+  if (numberOfSourceChannels === 4 && numberOfDestinationChannels === 1) {
+    var sourceChannel0 = source.getChannelData(0);
+    var sourceChannel1 = source.getChannelData(1);
+    var sourceChannel2 = source.getChannelData(2);
+    var sourceChannel3 = source.getChannelData(3);
+    var destinationChannel0 = destination.getChannelData(0);
+    for (i = 0; i < length; i++) {
+      destinationChannel0[i] += 0.25 * (sourceChannel0[i] + sourceChannel1[i]

[Raymond Toy, 2016/03/08 18:04:07]

Again, this doesn't match the comment.  Update comment or code.

[hongchan, 2016/03/08 23:53:35]

Done.

+        + sourceChannel2[i] + sourceChannel3[i]);
+    }
+
+    return;
+  }
+
+  // Down-mixing: 5.1 -> 1
+  //   output = sqrt(1/2) * (input.L + input.R) + input.C
+  //            + 0.5 * (input.SL + input.SR)
+  if (numberOfSourceChannels === 6 && numberOfDestinationChannels === 1) {
+    var sourceChannel0 = source.getChannelData(0);
+    var sourceChannel1 = source.getChannelData(1);
+    var sourceChannel2 = source.getChannelData(2);
+    var sourceChannel4 = source.getChannelData(4);
+    var sourceChannel5 = source.getChannelData(5);
+    var destinationChannel0 = destination.getChannelData(0);
+    var scaleSqrtHalf = Math.sqrt(0.5);
+    for (i = 0; i < length; i++) {
+      destinationChannel0[i] +=

[Raymond Toy, 2016/03/08 18:04:07]

This doesn't match the comment.  Update comment or code.

[hongchan, 2016/03/08 23:53:34]

Done.

+        scaleSqrtHalf * (sourceChannel0[i] + sourceChannel1[i])
+        + sourceChannel2[i] + 0.5 * (sourceChannel4[i] + sourceChannel5[i]);
+    }
+
+    return;
+  }
+
+  // Down-mixing: 4 -> 2
+  //   output.L = 0.5 * (input.L + input.SL)
+  //   output.R = 0.5 * (input.R + input.SR)
+  if (numberOfSourceChannels == 4 && numberOfDestinationChannels == 2) {
+    var sourceChannel0 = source.getChannelData(0);

[Raymond Toy, 2016/03/08 18:04:07]

Probably want to say how sourceChannel<n> is assigned to input.<name>.  Here and
below.

[hongchan, 2016/03/08 23:53:34]

Done.

+    var sourceChannel1 = source.getChannelData(1);
+    var sourceChannel2 = source.getChannelData(2);
+    var sourceChannel3 = source.getChannelData(3);
+    var destinationChannel0 = destination.getChannelData(0);
+    var destinationChannel1 = destination.getChannelData(1);
+    for (i = 0; i < length; i++) {
+      destinationChannel0[i] += 0.5 * (sourceChannel0[i] + sourceChannel2[i]);
+      destinationChannel1[i] += 0.5 * (sourceChannel1[i] + sourceChannel3[i]);

[Raymond Toy, 2016/03/08 18:04:07]

This doesn't match the comment.  Update comment or code.

[hongchan, 2016/03/08 23:53:35]

Done.

+    }
+
+    return;
+  }
+
+  // Down-mixing: 5.1 -> 2
+  //   output.L = input.L + sqrt(1/2) * (input.C + input.SL)
+  //   output.R = input.R + sqrt(1/2) * (input.C + input.SR)
+  if (numberOfSourceChannels == 6 && numberOfDestinationChannels == 2) {
+    var sourceChannel0 = source.getChannelData(0);
+    var sourceChannel1 = source.getChannelData(1);
+    var sourceChannel2 = source.getChannelData(2);
+    var sourceChannel4 = source.getChannelData(4);
+    var sourceChannel5 = source.getChannelData(5);
+    var destinationChannel0 = destination.getChannelData(0);
+    var destinationChannel1 = destination.getChannelData(1);
+    var scaleSqrtHalf = Math.sqrt(0.5);
+    for (i = 0; i < length; i++) {
+      destinationChannel0[i] += sourceChannel0[i]
+        + scaleSqrtHalf * (sourceChannel2[i] + sourceChannel4[i]);
+      destinationChannel1[i] += sourceChannel1[i]
+        + scaleSqrtHalf * (sourceChannel2[i] + sourceChannel5[i]);
+    }
+
+    return;
+  }
+
+  // Down-mixing: 5.1 -> 4
+  //   output.L = input.L + sqrt(1/2) * input.C
+  //   output.R = input.R + sqrt(1/2) * input.C
+  //   output.SL = input.SL
+  //   output.SR = input.SR
+  if (numberOfSourceChannels === 6 && numberOfDestinationChannels === 4) {
+    var sourceChannel0 = source.getChannelData(0);
+    var sourceChannel1 = source.getChannelData(1);
+    var sourceChannel2 = source.getChannelData(2);
+    var sourceChannel4 = source.getChannelData(4);
+    var sourceChannel5 = source.getChannelData(5);
+    var destinationChannel0 = destination.getChannelData(0);
+    var destinationChannel1 = destination.getChannelData(1);
+    var destinationChannel2 = destination.getChannelData(2);
+    var destinationChannel3 = destination.getChannelData(3);
+    var scaleSqrtHalf = Math.sqrt(0.5);
+    for (i = 0; i < length; i++) {
+      destinationChannel0[i] += sourceChannel0[i] + scaleSqrtHalf * sourceChannel2[i];
+      destinationChannel1[i] += sourceChannel1[i] + scaleSqrtHalf * sourceChannel2[i];
+      destinationChannel2[i] += sourceChannel4[i];
+      destinationChannel3[i] += sourceChannel5[i];
+    }
+
+    return;
+  }
+
+  // All other cases, fall back to the discrete sum.
+  discreteSum(source, destination);
+}