Expose the internal MatrixBuilder class as ChannelMixingMatrix.

media/base/channel_mixing_matrix.h

Index: media/base/channel_mixing_matrix.h
diff --git a/media/base/channel_mixing_matrix.h b/media/base/channel_mixing_matrix.h
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+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef MEDIA_BASE_CHANNEL_MIXING_MATRIX_H_
+#define MEDIA_BASE_CHANNEL_MIXING_MATRIX_H_
+
+#include <vector>
+
+#include "base/macros.h"
+#include "media/base/channel_layout.h"
+#include "media/base/media_export.h"
+
+namespace media {
+
+class MEDIA_EXPORT ChannelMixingMatrix {
+ public:
+  ChannelMixingMatrix(ChannelLayout input_layout,
+                      int input_channels,
+                      ChannelLayout output_layout,
+                      int output_channels);
+
+  ~ChannelMixingMatrix();
+
+  // 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(ChannelMixingMatrix);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_CHANNEL_MIXING_MATRIX_H_