1 files changed, 136 insertions, 0 deletions
diff --git a/dom/media/webaudio/AudioBlock.h b/dom/media/webaudio/AudioBlock.h
new file mode 100644
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+++ b/dom/media/webaudio/AudioBlock.h
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+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim:set ts=2 sw=2 sts=2 et cindent: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+#ifndef MOZILLA_AUDIOBLOCK_H_
+#define MOZILLA_AUDIOBLOCK_H_
+
+#include "AudioSegment.h"
+
+namespace mozilla {
+
+/**
+ * An AudioChunk whose buffer contents need to be valid only for one
+ * processing block iteration, after which contents can be overwritten if the
+ * buffer has not been passed to longer term storage or to another thread,
+ * which may happen though AsAudioChunk() or AsMutableChunk().
+ *
+ * Use on graph thread only.
+ */
+class AudioBlock : private AudioChunk
+{
+public:
+  AudioBlock() {
+    mDuration = WEBAUDIO_BLOCK_SIZE;
+    mBufferFormat = AUDIO_FORMAT_SILENCE;
+  }
+  // No effort is made in constructors to ensure that mBufferIsDownstreamRef
+  // is set because the block is expected to be a temporary and so the
+  // reference will be released before the next iteration.
+  // The custom copy constructor is required so as not to set
+  // mBufferIsDownstreamRef without notifying AudioBlockBuffer.
+  AudioBlock(const AudioBlock& aBlock) : AudioChunk(aBlock.AsAudioChunk()) {}
+  explicit AudioBlock(const AudioChunk& aChunk)
+    : AudioChunk(aChunk)
+  {
+    MOZ_ASSERT(aChunk.mDuration == WEBAUDIO_BLOCK_SIZE);
+  }
+  ~AudioBlock();
+
+  using AudioChunk::GetDuration;
+  using AudioChunk::IsNull;
+  using AudioChunk::ChannelCount;
+  using AudioChunk::ChannelData;
+  using AudioChunk::SizeOfExcludingThisIfUnshared;
+  using AudioChunk::SizeOfExcludingThis;
+  // mDuration is not exposed.  Use GetDuration().
+  // mBuffer is not exposed.  Use SetBuffer().
+  using AudioChunk::mChannelData;
+  using AudioChunk::mVolume;
+  using AudioChunk::mBufferFormat;
+
+  const AudioChunk& AsAudioChunk() const { return *this; }
+  AudioChunk* AsMutableChunk() {
+    ClearDownstreamMark();
+    return this;
+  }
+
+  /**
+   * Allocates, if necessary, aChannelCount buffers of WEBAUDIO_BLOCK_SIZE float
+   * samples for writing.
+   */
+  void AllocateChannels(uint32_t aChannelCount);
+
+  /**
+   * ChannelFloatsForWrite() should only be used when the buffers have been
+   * created with AllocateChannels().
+   */
+  float* ChannelFloatsForWrite(size_t aChannel)
+  {
+    MOZ_ASSERT(mBufferFormat == AUDIO_FORMAT_FLOAT32);
+    MOZ_ASSERT(CanWrite());
+    return static_cast<float*>(const_cast<void*>(mChannelData[aChannel]));
+  }
+
+  void SetBuffer(ThreadSharedObject* aNewBuffer);
+  void SetNull(StreamTime aDuration) {
+    MOZ_ASSERT(aDuration == WEBAUDIO_BLOCK_SIZE);
+    SetBuffer(nullptr);
+    mChannelData.Clear();
+    mVolume = 1.0f;
+    mBufferFormat = AUDIO_FORMAT_SILENCE;
+  }
+
+  AudioBlock& operator=(const AudioBlock& aBlock) {
+    // Instead of just copying, mBufferIsDownstreamRef must be first cleared
+    // if set.  It is set again for the new mBuffer if possible.  This happens
+    // in SetBuffer().
+    return *this = aBlock.AsAudioChunk();
+  }
+  AudioBlock& operator=(const AudioChunk& aChunk) {
+    MOZ_ASSERT(aChunk.mDuration == WEBAUDIO_BLOCK_SIZE);
+    SetBuffer(aChunk.mBuffer);
+    mChannelData = aChunk.mChannelData;
+    mVolume = aChunk.mVolume;
+    mBufferFormat = aChunk.mBufferFormat;
+    return *this;
+  }
+
+  bool IsMuted() const { return mVolume == 0.0f; }
+
+  bool IsSilentOrSubnormal() const
+  {
+    if (!mBuffer) {
+      return true;
+    }
+
+    for (uint32_t i = 0, length = mChannelData.Length(); i < length; ++i) {
+      const float* channel = static_cast<const float*>(mChannelData[i]);
+      for (StreamTime frame = 0; frame < mDuration; ++frame) {
+        if (fabs(channel[frame]) >= FLT_MIN) {
+          return false;
+        }
+      }
+    }
+
+    return true;
+  }
+
+private:
+  void ClearDownstreamMark();
+  bool CanWrite();
+
+  // mBufferIsDownstreamRef is set only when mBuffer references an
+  // AudioBlockBuffer created in a different AudioBlock.  That can happen when
+  // this AudioBlock is on a node downstream from the node which created the
+  // buffer.  When this is set, the AudioBlockBuffer is notified that this
+  // reference does prevent the upstream node from re-using the buffer next
+  // iteration and modifying its contents.  The AudioBlockBuffer is also
+  // notified when mBuffer releases this reference.
+  bool mBufferIsDownstreamRef = false;
+};
+
+} // namespace mozilla
+
+#endif // MOZILLA_AUDIOBLOCK_H_