Bug 1558123 copy audio samples to/from JS arrays r=padenot

Direct use of aInput buffers for ArrayBuffer elements is not possible in
general.  aInput buffers are const because they may be used elsewhere but
ArrayBuffer elements may be modified by script.  If necessary, it would be
possible to later add a mechanism to mix inputs directly into the ArrayBuffer,
but often no mixing is required.

Direct use of output ArrayBuffer elements would require DetachArrayBuffer to
ensure the elements are not modified by script, but that would require
creation of a new ArrayBuffer JS object on each call.

https://github.com/WebAudio/web-audio-api/issues/1932 tracks specification of
making output data available for reading (for downstream node input).

Differential Revision: https://phabricator.services.mozilla.com/D34837

--HG--
extra : moz-landing-system : lando

dom/media/webaudio/AudioWorkletNode.cpp

@@ -269,6 +269,44 @@ void WorkletNodeEngine::ProcessBlocksOnPorts(AudioNodeStream* aStream,
     ProduceSilence(aOutput);
     return;
   }
+
+  // Copy input values to JS objects.
+  for (size_t i = 0; i < aInput.Length(); ++i) {
+    const AudioBlock& input = aInput[i];
+    size_t channelCount = input.ChannelCount();
+    if (channelCount == 0) {
+      // Null blocks have AUDIO_FORMAT_SILENCE.
+      // Don't call ChannelData<float>().
+      continue;
+    }
+    float volume = input.mVolume;
+    const auto& channelData = input.ChannelData<float>();
+    const auto& float32Arrays = mInputs.mPorts[i].mFloat32Arrays;
+    JS::AutoCheckCannotGC nogc;
+    for (size_t c = 0; c < channelCount; ++c) {
+      bool isShared;
+      float* dest = JS_GetFloat32ArrayData(float32Arrays[c], &isShared, nogc);
+      MOZ_ASSERT(!isShared);  // Was created as unshared
+      AudioBlockCopyChannelWithScale(channelData[c], volume, dest);
+    }
+  }
+
+  // TODO call process() - bug 1558123
+
+  // Copy output values from JS objects.
+  for (size_t o = 0; o < aOutput.Length(); ++o) {
+    AudioBlock* output = &aOutput[o];
+    size_t channelCount = output->ChannelCount();
+    const auto& float32Arrays = mOutputs.mPorts[o].mFloat32Arrays;
+    JS::AutoCheckCannotGC nogc;
+    for (size_t c = 0; c < channelCount; ++c) {
+      bool isShared;
+      const float* src =
+          JS_GetFloat32ArrayData(float32Arrays[c], &isShared, nogc);
+      MOZ_ASSERT(!isShared);  // Was created as unshared
+      PodCopy(output->ChannelFloatsForWrite(c), src, WEBAUDIO_BLOCK_SIZE);
+    }
+  }
 }
 
 AudioWorkletNode::AudioWorkletNode(AudioContext* aAudioContext,