Expose the internal MatrixBuilder class as ChannelMixingMatrix.

media/base/channel_mixer.cc

Index: media/base/channel_mixer.cc
diff --git a/media/base/channel_mixer.cc b/media/base/channel_mixer.cc
index ef1bd5c096e96421f2fc6c02fce1ea3a3f57fa42..54b59a891794942c6b494265a2aa36bce59806ff 100644
--- a/media/base/channel_mixer.cc
+++ b/media/base/channel_mixer.cc
@@ -2,114 +2,16 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// MSVC++ requires this to be set before any other includes to get M_SQRT1_2.
-#define _USE_MATH_DEFINES
-
 #include "media/base/channel_mixer.h"
 
-#include <algorithm>
-#include <cmath>
-
 #include "base/logging.h"
 #include "media/audio/audio_parameters.h"
 #include "media/base/audio_bus.h"
+#include "media/base/channel_mixing_matrix.h"
 #include "media/base/vector_math.h"
 
 namespace media {
 
-// Default scale factor for mixing two channels together.  We use a different
-// value for stereo -> mono and mono -> stereo mixes.
-static const float kEqualPowerScale = static_cast<float>(M_SQRT1_2);
-
-static void ValidateLayout(ChannelLayout layout) {
-  CHECK_NE(layout, CHANNEL_LAYOUT_NONE);
-  CHECK_LE(layout, CHANNEL_LAYOUT_MAX);
-  CHECK_NE(layout, CHANNEL_LAYOUT_UNSUPPORTED);
-  CHECK_NE(layout, CHANNEL_LAYOUT_DISCRETE);
-  CHECK_NE(layout, CHANNEL_LAYOUT_STEREO_AND_KEYBOARD_MIC);
-
-  // Verify there's at least one channel.  Should always be true here by virtue
-  // of not being one of the invalid layouts, but lets double check to be sure.
-  int channel_count = ChannelLayoutToChannelCount(layout);
-  DCHECK_GT(channel_count, 0);
-
-  // If we have more than one channel, verify a symmetric layout for sanity.
-  // The unit test will verify all possible layouts, so this can be a DCHECK.
-  // Symmetry allows simplifying the matrix building code by allowing us to
-  // assume that if one channel of a pair exists, the other will too.
-  if (channel_count > 1) {
-    // Assert that LEFT exists if and only if RIGHT exists, and so on.
-    DCHECK_EQ(ChannelOrder(layout, LEFT) >= 0,
-              ChannelOrder(layout, RIGHT) >= 0);
-    DCHECK_EQ(ChannelOrder(layout, SIDE_LEFT) >= 0,
-              ChannelOrder(layout, SIDE_RIGHT) >= 0);
-    DCHECK_EQ(ChannelOrder(layout, BACK_LEFT) >= 0,
-              ChannelOrder(layout, BACK_RIGHT) >= 0);
-    DCHECK_EQ(ChannelOrder(layout, LEFT_OF_CENTER) >= 0,
-              ChannelOrder(layout, RIGHT_OF_CENTER) >= 0);
-  } else {
-    DCHECK_EQ(layout, CHANNEL_LAYOUT_MONO);
-  }
-}
-
-class MatrixBuilder {
- public:
-  MatrixBuilder(ChannelLayout input_layout, int input_channels,
-                ChannelLayout output_layout, int output_channels)
-      : input_layout_(input_layout),
-        input_channels_(input_channels),
-        output_layout_(output_layout),
-        output_channels_(output_channels) {
-    // Special case for 5.0, 5.1 with back channels when upmixed to 7.0, 7.1,
-    // which should map the back LR to side LR.
-    if (input_layout_ == CHANNEL_LAYOUT_5_0_BACK &&
-        output_layout_ == CHANNEL_LAYOUT_7_0) {
-      input_layout_ = CHANNEL_LAYOUT_5_0;
-    } else if (input_layout_ == CHANNEL_LAYOUT_5_1_BACK &&
-               output_layout_ == CHANNEL_LAYOUT_7_1) {
-      input_layout_ = CHANNEL_LAYOUT_5_1;
-    }
-  }
-
-  ~MatrixBuilder() { }
-
-  // Create the transformation matrix of input channels to output channels.
-  // Updates the empty matrix with the transformation, and returns true
-  // if the transformation is just a remapping of channels (no mixing).
-  bool CreateTransformationMatrix(std::vector< std::vector<float> >* matrix);
-
- private:
-  // Result transformation of input channels to output channels
-  std::vector< std::vector<float> >* matrix_;
-
-  // Input and output channel layout provided during construction.
-  ChannelLayout input_layout_;
-  int input_channels_;
-  ChannelLayout output_layout_;
-  int output_channels_;
-
-  // Helper variable for tracking which inputs are currently unaccounted,
-  // should be empty after construction completes.
-  std::vector<Channels> unaccounted_inputs_;
-
-  // Helper methods for managing unaccounted input channels.
-  void AccountFor(Channels ch);
-  bool IsUnaccounted(Channels ch) const;
-
-  // Helper methods for checking if |ch| exists in either |input_layout_| or
-  // |output_layout_| respectively.
-  bool HasInputChannel(Channels ch) const;
-  bool HasOutputChannel(Channels ch) const;
-
-  // Helper methods for updating |matrix_| with the proper value for
-  // mixing |input_ch| into |output_ch|.  MixWithoutAccounting() does not
-  // remove the channel from |unaccounted_inputs_|.
-  void Mix(Channels input_ch, Channels output_ch, float scale);
-  void MixWithoutAccounting(Channels input_ch, Channels output_ch, float scale);
-
-  DISALLOW_COPY_AND_ASSIGN(MatrixBuilder);
-};
-
 ChannelMixer::ChannelMixer(ChannelLayout input_layout,
                            ChannelLayout output_layout) {
   Initialize(input_layout,
@@ -129,203 +31,12 @@ ChannelMixer::ChannelMixer(
 void ChannelMixer::Initialize(
     ChannelLayout input_layout, int input_channels,
     ChannelLayout output_layout, int output_channels) {
-  // Stereo down mix should never be the output layout.
-  CHECK_NE(output_layout, CHANNEL_LAYOUT_STEREO_DOWNMIX);
-
-  // Verify that the layouts are supported
-  if (input_layout != CHANNEL_LAYOUT_DISCRETE)
-    ValidateLayout(input_layout);
-  if (output_layout != CHANNEL_LAYOUT_DISCRETE)
-    ValidateLayout(output_layout);
-
   // Create the transformation matrix
-  MatrixBuilder matrix_builder(input_layout, input_channels,
-                               output_layout, output_channels);
+  ChannelMixingMatrix matrix_builder(input_layout, input_channels,
+                                     output_layout, output_channels);
   remapping_ = matrix_builder.CreateTransformationMatrix(&matrix_);
 }
 
-bool MatrixBuilder::CreateTransformationMatrix(
-    std::vector< std::vector<float> >* matrix) {
-  matrix_ = matrix;
-
-  // Size out the initial matrix.
-  matrix_->reserve(output_channels_);
-  for (int output_ch = 0; output_ch < output_channels_; ++output_ch)
-    matrix_->push_back(std::vector<float>(input_channels_, 0));
-
-  // First check for discrete case.
-  if (input_layout_ == CHANNEL_LAYOUT_DISCRETE ||
-      output_layout_ == CHANNEL_LAYOUT_DISCRETE) {
-    // If the number of input channels is more than output channels, then
-    // copy as many as we can then drop the remaining input channels.
-    // If the number of input channels is less than output channels, then
-    // copy them all, then zero out the remaining output channels.
-    int passthrough_channels = std::min(input_channels_, output_channels_);
-    for (int i = 0; i < passthrough_channels; ++i)
-      (*matrix_)[i][i] = 1;
-
-    return true;
-  }
-
-  // Route matching channels and figure out which ones aren't accounted for.
-  for (Channels ch = LEFT; ch < CHANNELS_MAX + 1;
-       ch = static_cast<Channels>(ch + 1)) {
-    int input_ch_index = ChannelOrder(input_layout_, ch);
-    if (input_ch_index < 0)
-      continue;
-
-    int output_ch_index = ChannelOrder(output_layout_, ch);
-    if (output_ch_index < 0) {
-      unaccounted_inputs_.push_back(ch);
-      continue;
-    }
-
-    DCHECK_LT(static_cast<size_t>(output_ch_index), matrix_->size());
-    DCHECK_LT(static_cast<size_t>(input_ch_index),
-              (*matrix_)[output_ch_index].size());
-    (*matrix_)[output_ch_index][input_ch_index] = 1;
-  }
-
-  // If all input channels are accounted for, there's nothing left to do.
-  if (unaccounted_inputs_.empty()) {
-    // Since all output channels map directly to inputs we can optimize.
-    return true;
-  }
-
-  // Mix front LR into center.
-  if (IsUnaccounted(LEFT)) {
-    // When down mixing to mono from stereo, we need to be careful of full scale
-    // stereo mixes.  Scaling by 1 / sqrt(2) here will likely lead to clipping
-    // so we use 1 / 2 instead.
-    float scale =
-        (output_layout_ == CHANNEL_LAYOUT_MONO && input_channels_ == 2) ?
-        0.5 : kEqualPowerScale;
-    Mix(LEFT, CENTER, scale);
-    Mix(RIGHT, CENTER, scale);
-  }
-
-  // Mix center into front LR.
-  if (IsUnaccounted(CENTER)) {
-    // When up mixing from mono, just do a copy to front LR.
-    float scale =
-        (input_layout_ == CHANNEL_LAYOUT_MONO) ? 1 : kEqualPowerScale;
-    MixWithoutAccounting(CENTER, LEFT, scale);
-    Mix(CENTER, RIGHT, scale);
-  }
-
-  // Mix back LR into: side LR || back center || front LR || front center.
-  if (IsUnaccounted(BACK_LEFT)) {
-    if (HasOutputChannel(SIDE_LEFT)) {
-      // If the input has side LR, mix back LR into side LR, but instead if the
-      // input doesn't have side LR (but output does) copy back LR to side LR.
-      float scale = HasInputChannel(SIDE_LEFT) ? kEqualPowerScale : 1;
-      Mix(BACK_LEFT, SIDE_LEFT, scale);
-      Mix(BACK_RIGHT, SIDE_RIGHT, scale);
-    } else if (HasOutputChannel(BACK_CENTER)) {
-      // Mix back LR into back center.
-      Mix(BACK_LEFT, BACK_CENTER, kEqualPowerScale);
-      Mix(BACK_RIGHT, BACK_CENTER, kEqualPowerScale);
-    } else if (output_layout_ > CHANNEL_LAYOUT_MONO) {
-      // Mix back LR into front LR.
-      Mix(BACK_LEFT, LEFT, kEqualPowerScale);
-      Mix(BACK_RIGHT, RIGHT, kEqualPowerScale);
-    } else {
-      // Mix back LR into front center.
-      Mix(BACK_LEFT, CENTER, kEqualPowerScale);
-      Mix(BACK_RIGHT, CENTER, kEqualPowerScale);
-    }
-  }
-
-  // Mix side LR into: back LR || back center || front LR || front center.
-  if (IsUnaccounted(SIDE_LEFT)) {
-    if (HasOutputChannel(BACK_LEFT)) {
-      // If the input has back LR, mix side LR into back LR, but instead if the
-      // input doesn't have back LR (but output does) copy side LR to back LR.
-      float scale = HasInputChannel(BACK_LEFT) ? kEqualPowerScale : 1;
-      Mix(SIDE_LEFT, BACK_LEFT, scale);
-      Mix(SIDE_RIGHT, BACK_RIGHT, scale);
-    } else if (HasOutputChannel(BACK_CENTER)) {
-      // Mix side LR into back center.
-      Mix(SIDE_LEFT, BACK_CENTER, kEqualPowerScale);
-      Mix(SIDE_RIGHT, BACK_CENTER, kEqualPowerScale);
-    } else if (output_layout_ > CHANNEL_LAYOUT_MONO) {
-      // Mix side LR into front LR.
-      Mix(SIDE_LEFT, LEFT, kEqualPowerScale);
-      Mix(SIDE_RIGHT, RIGHT, kEqualPowerScale);
-    } else {
-      // Mix side LR into front center.
-      Mix(SIDE_LEFT, CENTER, kEqualPowerScale);
-      Mix(SIDE_RIGHT, CENTER, kEqualPowerScale);
-    }
-  }
-
-  // Mix back center into: back LR || side LR || front LR || front center.
-  if (IsUnaccounted(BACK_CENTER)) {
-    if (HasOutputChannel(BACK_LEFT)) {
-      // Mix back center into back LR.
-      MixWithoutAccounting(BACK_CENTER, BACK_LEFT, kEqualPowerScale);
-      Mix(BACK_CENTER, BACK_RIGHT, kEqualPowerScale);
-    } else if (HasOutputChannel(SIDE_LEFT)) {
-      // Mix back center into side LR.
-      MixWithoutAccounting(BACK_CENTER, SIDE_LEFT, kEqualPowerScale);
-      Mix(BACK_CENTER, SIDE_RIGHT, kEqualPowerScale);
-    } else if (output_layout_ > CHANNEL_LAYOUT_MONO) {
-      // Mix back center into front LR.
-      // TODO(dalecurtis): Not sure about these values?
-      MixWithoutAccounting(BACK_CENTER, LEFT, kEqualPowerScale);
-      Mix(BACK_CENTER, RIGHT, kEqualPowerScale);
-    } else {
-      // Mix back center into front center.
-      // TODO(dalecurtis): Not sure about these values?
-      Mix(BACK_CENTER, CENTER, kEqualPowerScale);
-    }
-  }
-
-  // Mix LR of center into: front LR || front center.
-  if (IsUnaccounted(LEFT_OF_CENTER)) {
-    if (HasOutputChannel(LEFT)) {
-      // Mix LR of center into front LR.
-      Mix(LEFT_OF_CENTER, LEFT, kEqualPowerScale);
-      Mix(RIGHT_OF_CENTER, RIGHT, kEqualPowerScale);
-    } else {
-      // Mix LR of center into front center.
-      Mix(LEFT_OF_CENTER, CENTER, kEqualPowerScale);
-      Mix(RIGHT_OF_CENTER, CENTER, kEqualPowerScale);
-    }
-  }
-
-  // Mix LFE into: front center || front LR.
-  if (IsUnaccounted(LFE)) {
-    if (!HasOutputChannel(CENTER)) {
-      // Mix LFE into front LR.
-      MixWithoutAccounting(LFE, LEFT, kEqualPowerScale);
-      Mix(LFE, RIGHT, kEqualPowerScale);
-    } else {
-      // Mix LFE into front center.
-      Mix(LFE, CENTER, kEqualPowerScale);
-    }
-  }
-
-  // All channels should now be accounted for.
-  DCHECK(unaccounted_inputs_.empty());
-
-  // See if the output |matrix_| is simply a remapping matrix.  If each input
-  // channel maps to a single output channel we can simply remap.  Doing this
-  // programmatically is less fragile than logic checks on channel mappings.
-  for (int output_ch = 0; output_ch < output_channels_; ++output_ch) {
-    int input_mappings = 0;
-    for (int input_ch = 0; input_ch < input_channels_; ++input_ch) {
-      // We can only remap if each row contains a single scale of 1.  I.e., each
-      // output channel is mapped from a single unscaled input channel.
-      if ((*matrix_)[output_ch][input_ch] != 1 || ++input_mappings > 1)
-        return false;
-    }
-  }
-
-  // If we've gotten here, |matrix_| is simply a remapping.
-  return true;
-}
-
 ChannelMixer::~ChannelMixer() {}
 
 void ChannelMixer::Transform(const AudioBus* input, AudioBus* output) {
@@ -365,40 +76,4 @@ void ChannelMixer::Transform(const AudioBus* input, AudioBus* output) {
   }
 }
 
-void MatrixBuilder::AccountFor(Channels ch) {
-  unaccounted_inputs_.erase(std::find(
-      unaccounted_inputs_.begin(), unaccounted_inputs_.end(), ch));
-}
-
-bool MatrixBuilder::IsUnaccounted(Channels ch) const {
-  return std::find(unaccounted_inputs_.begin(), unaccounted_inputs_.end(),
-                   ch) != unaccounted_inputs_.end();
-}
-
-bool MatrixBuilder::HasInputChannel(Channels ch) const {
-  return ChannelOrder(input_layout_, ch) >= 0;
-}
-
-bool MatrixBuilder::HasOutputChannel(Channels ch) const {
-  return ChannelOrder(output_layout_, ch) >= 0;
-}
-
-void MatrixBuilder::Mix(Channels input_ch, Channels output_ch, float scale) {
-  MixWithoutAccounting(input_ch, output_ch, scale);
-  AccountFor(input_ch);
-}
-
-void MatrixBuilder::MixWithoutAccounting(Channels input_ch, Channels output_ch,
-                                         float scale) {
-  int input_ch_index = ChannelOrder(input_layout_, input_ch);
-  int output_ch_index = ChannelOrder(output_layout_, output_ch);
-
-  DCHECK(IsUnaccounted(input_ch));
-  DCHECK_GE(input_ch_index, 0);
-  DCHECK_GE(output_ch_index, 0);
-
-  DCHECK_EQ((*matrix_)[output_ch_index][input_ch_index], 0);
-  (*matrix_)[output_ch_index][input_ch_index] = scale;
-}
-
 }  // namespace media