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vag.cpp

/* ScummVM - Graphic Adventure Engine
 *
 * ScummVM is the legal property of its developers, whose names
 * are too numerous to list here. Please refer to the COPYRIGHT
 * file distributed with this source distribution.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.

 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.

 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 *
 * $URL$
 * $Id$
 *
 */

#include "audio/decoders/vag.h"
#include "audio/audiostream.h"
#include "common/stream.h"

namespace Audio {

00032 class VagStream : public Audio::RewindableAudioStream {
public:
      VagStream(Common::SeekableReadStream *stream, int rate);
      ~VagStream();

00037       bool isStereo() const { return false; }
00038       bool endOfData() const { return _stream->pos() == _stream->size(); }
00039       int getRate() const { return _rate; }
      int readBuffer(int16 *buffer, const int numSamples);

      bool rewind();
private:
      Common::SeekableReadStream *_stream;

      byte _predictor;
      double _samples[28];
      byte _samplesRemaining;
      int _rate;
      double _s1, _s2;
};

VagStream::VagStream(Common::SeekableReadStream *stream, int rate) : _stream(stream) {
      _samplesRemaining = 0;
      _predictor = 0;
      _s1 = _s2 = 0.0;
      _rate = rate;
}


VagStream::~VagStream() {
      delete _stream;
}

static const double s_vagDataTable[5][2] =
      {
            {  0.0, 0.0 },
            {  60.0 / 64.0,  0.0 },
            {  115.0 / 64.0, -52.0 / 64.0 },
            {  98.0 / 64.0, -55.0 / 64.0 },
            {  122.0 / 64.0, -60.0 / 64.0 }
      };

00074 int VagStream::readBuffer(int16 *buffer, const int numSamples) {
      int32 samplesDecoded = 0;

      if (_samplesRemaining) {
            byte i = 0;

            for (i = 28 - _samplesRemaining; i < 28 && samplesDecoded < numSamples; i++) {
                  _samples[i] = _samples[i] + _s1 * s_vagDataTable[_predictor][0] + _s2 * s_vagDataTable[_predictor][1];
                  _s2 = _s1;
                  _s1 = _samples[i];
                  int16 d = (int) (_samples[i] + 0.5);
                  buffer[samplesDecoded] = d;
                  samplesDecoded++;
            }

#if 0
            assert(i == 28); // We're screwed if this fails :P
#endif
            // This might mean the file is corrupted, or that the stream has
            // been closed.
            if (i != 28) return 0;

            _samplesRemaining = 0;
      }

      while (samplesDecoded < numSamples) {
            byte i = 0;

            _predictor = _stream->readByte();
            byte shift = _predictor & 0xf;
            _predictor >>= 4;

            if (_stream->readByte() == 7)
                  return samplesDecoded;

            for (i = 0; i < 28; i += 2) {
                  byte d = _stream->readByte();
                  int16 s = (d & 0xf) << 12;
                  if (s & 0x8000)
                        s |= 0xffff0000;
                  _samples[i] = (double)(s >> shift);
                  s = (d & 0xf0) << 8;
                  if (s & 0x8000)
                        s |= 0xffff0000;
                  _samples[i + 1] = (double)(s >> shift);
            }

            for (i = 0; i < 28 && samplesDecoded < numSamples; i++) {
                  _samples[i] = _samples[i] + _s1 * s_vagDataTable[_predictor][0] + _s2 * s_vagDataTable[_predictor][1];
                  _s2 = _s1;
                  _s1 = _samples[i];
                  int16 d = (int) (_samples[i] + 0.5);
                  buffer[samplesDecoded] = d;
                  samplesDecoded++;
            }

            if (i != 27)
                  _samplesRemaining = 28 - i;
      }

      return samplesDecoded;
}

00137 bool VagStream::rewind() {
      _stream->seek(0);
      _samplesRemaining = 0;
      _predictor = 0;
      _s1 = _s2 = 0.0;

      return true;
}

00146 RewindableAudioStream *makeVagStream(Common::SeekableReadStream *stream, int rate) {
      return new VagStream(stream, rate);
}

}

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