Make ConvolverNode conform to spec

third_party/WebKit/Source/platform/audio/Reverb.cpp

Index: third_party/WebKit/Source/platform/audio/Reverb.cpp
diff --git a/third_party/WebKit/Source/platform/audio/Reverb.cpp b/third_party/WebKit/Source/platform/audio/Reverb.cpp
index 32c62acfe1903e73195d6d4b07786e82819630a9..b396f3cab7f36749b927498dd1c3f748448700ae 100644
--- a/third_party/WebKit/Source/platform/audio/Reverb.cpp
+++ b/third_party/WebKit/Source/platform/audio/Reverb.cpp
@@ -119,15 +119,18 @@ void Reverb::initialize(AudioBus* impulseResponseBuffer,
                         size_t numberOfChannels,
                         bool useBackgroundThreads) {
   m_impulseResponseLength = impulseResponseBuffer->length();
+  m_numberOfChannels = numberOfChannels;
 
   // The reverb can handle a mono impulse response and still do stereo
   // processing

[hongchan, 2017/03/28 16:44:35]

nit: a missing period.

   size_t numResponseChannels = impulseResponseBuffer->numberOfChannels();

[hongchan, 2017/03/28 16:44:35]

This can be unsigned.

[Raymond Toy, 2017/03/28 18:26:50]

This requires changing various other bits of code because it's operated on with
size_t objects too.

-  m_convolvers.reserveCapacity(numberOfChannels);
+  size_t numConvolvers = std::max(numResponseChannels, static_cast<size_t>(2));
+  m_convolvers.reserveCapacity(numConvolvers);

[hongchan, 2017/03/28 16:44:35]

Is |numConvolvers| properly named? Isn't it more of |numberOfConvolverChannels|?

[Raymond Toy, 2017/03/28 18:17:20]

numberOfConvolverChannels is confusing too since the number of responses isn't
the same as this.

numberOfConvolvers is probably closest since it's the size of m_convolvers?

 
   int convolverRenderPhase = 0;
-  for (size_t i = 0; i < numResponseChannels; ++i) {
-    AudioChannel* channel = impulseResponseBuffer->channel(i);
+  for (size_t i = 0; i < numConvolvers; ++i) {
+    AudioChannel* channel =
+        impulseResponseBuffer->channel(std::min(i, numResponseChannels - 1));
 
     std::unique_ptr<ReverbConvolver> convolver = WTF::wrapUnique(
         new ReverbConvolver(channel, renderSliceSize, maxFFTSize,
@@ -173,11 +176,42 @@ void Reverb::process(const AudioBus* sourceBus,
   // Handle input -> output matrixing...
   size_t numInputChannels = sourceBus->numberOfChannels();
   size_t numOutputChannels = destinationBus->numberOfChannels();
-  size_t numReverbChannels = m_convolvers.size();
-
-  if (numInputChannels == 2 && numReverbChannels == 2 &&
+  size_t numReverbChannels = m_numberOfChannels;

[hongchan, 2017/03/28 16:44:35]

I can't make a clear distinction between numReverbChannel, numConvolver,
numberOfChannel. We might want to rethink about these names.

[Raymond Toy, 2017/03/28 18:17:20]

numReverbChannels is the number of channels in the reverb buffer.
numReverbChannels should be renamed to numberOfResponseChannels. (Probably want
to rename m_numberOfChannels to m_numberOfResponseChannels?)

numConvolver is the length of m_convolvers.

I'll rename some of these.

[hongchan, 2017/03/28 19:01:44]

Yeah, this name seems to be problematic.

+
+  DCHECK_LE(numInputChannels, 2ul);
+  DCHECK_LE(numOutputChannels, 2ul);
+  DCHECK(numReverbChannels == 1 || numReverbChannels == 2 ||
+         numReverbChannels == 4);
+
+  // These are the possible combinations of number inputs, response
+  // channels and outputs channels that need to be supported:
+  //
+  //   numInputChannels: 1 or 2
+  //   numReverbChannels: 1, 2, or 4
+  //   numOutputChannels: 1 or 2
+  //
+  // Not all possible combinations are valid.  numOutputChannels is
+  // one only if both numInputChannels and numReverbChannels are 1.
+  // Otherwise numOutputChannels MUST be 2.
+  //
+  // The valid combinations are
+  //
+  //   Case     in -> resp -> out
+  //   1        1 -> 1 -> 1
+  //   2        1 -> 2 -> 2
+  //   3        1 -> 4 -> 2
+  //   4        2 -> 1 -> 2
+  //   5        2 -> 2 -> 2
+  //   6        2 -> 4 -> 2
+
+  if (numInputChannels == 2 &&
+      (numReverbChannels == 1 || numReverbChannels == 2) &&
       numOutputChannels == 2) {
-    // 2 -> 2 -> 2
+    // Case 4 and 5: 2 -> 2 -> 2 or 2 -> 1 -> 2.
+    //
+    // These can be handled in the same way because in the latter
+    // case, two connvolvers are still created with the second being a
+    // copy of the first.
     const AudioChannel* sourceChannelR = sourceBus->channel(1);
     AudioChannel* destinationChannelR = destinationBus->channel(1);
     m_convolvers[0]->process(sourceChannelL, destinationChannelL,
@@ -186,37 +220,20 @@ void Reverb::process(const AudioBus* sourceBus,
                              framesToProcess);
   } else if (numInputChannels == 1 && numOutputChannels == 2 &&
              numReverbChannels == 2) {
-    // 1 -> 2 -> 2
+    // Case 2: 1 -> 2 -> 2
     for (int i = 0; i < 2; ++i) {
       AudioChannel* destinationChannel = destinationBus->channel(i);
       m_convolvers[i]->process(sourceChannelL, destinationChannel,
                                framesToProcess);
     }
-  } else if (numInputChannels == 1 && numReverbChannels == 1 &&
-             numOutputChannels == 2) {
-    // 1 -> 1 -> 2
-    m_convolvers[0]->process(sourceChannelL, destinationChannelL,
-                             framesToProcess);
-
-    // simply copy L -> R
-    AudioChannel* destinationChannelR = destinationBus->channel(1);
-    bool isCopySafe = destinationChannelL->data() &&
-                      destinationChannelR->data() &&
-                      destinationChannelL->length() >= framesToProcess &&
-                      destinationChannelR->length() >= framesToProcess;
-    ASSERT(isCopySafe);
-    if (!isCopySafe)
-      return;
-    memcpy(destinationChannelR->mutableData(), destinationChannelL->data(),
-           sizeof(float) * framesToProcess);
-  } else if (numInputChannels == 1 && numReverbChannels == 1 &&
-             numOutputChannels == 1) {
-    // 1 -> 1 -> 1
+  } else if (numInputChannels == 1 && numReverbChannels == 1) {
+    // Case 1: 1 -> 1 -> 1
+    DCHECK_EQ(numOutputChannels, 1ul);
     m_convolvers[0]->process(sourceChannelL, destinationChannelL,
                              framesToProcess);
   } else if (numInputChannels == 2 && numReverbChannels == 4 &&
              numOutputChannels == 2) {
-    // 2 -> 4 -> 2 ("True" stereo)
+    // Case 6: 2 -> 4 -> 2 ("True" stereo)
     const AudioChannel* sourceChannelR = sourceBus->channel(1);
     AudioChannel* destinationChannelR = destinationBus->channel(1);
 
@@ -236,9 +253,9 @@ void Reverb::process(const AudioBus* sourceBus,
     destinationBus->sumFrom(*m_tempBuffer);
   } else if (numInputChannels == 1 && numReverbChannels == 4 &&
              numOutputChannels == 2) {
-    // 1 -> 4 -> 2 (Processing mono with "True" stereo impulse response)
-    // This is an inefficient use of a four-channel impulse response, but we
-    // should handle the case.
+    // Case 3: 1 -> 4 -> 2 (Processing mono with "True" stereo impulse
+    // response) This is an inefficient use of a four-channel impulse
+    // response, but we should handle the case.
     AudioChannel* destinationChannelR = destinationBus->channel(1);
 
     AudioChannel* tempChannelL = m_tempBuffer->channel(0);
@@ -256,8 +273,7 @@ void Reverb::process(const AudioBus* sourceBus,
 
     destinationBus->sumFrom(*m_tempBuffer);
   } else {
-    // Handle gracefully any unexpected / unsupported matrixing
-    // FIXME: add code for 5.1 support...
+    NOTREACHED();
     destinationBus->zero();
   }
 }