Method Acquire

libraries/lib-mixer/MixerSource.cpp:331–375

#define stackAllocate(T, count) static_cast<T*>(alloca(count * sizeof(T)))

std::optional<size_t> MixerSource::Acquire(Buffers &data, size_t bound)
{
   assert(AcceptsBuffers(data));
   assert(AcceptsBlockSize(data.BlockSize()));
   assert(bound <= data.BlockSize());
   assert(data.BlockSize() <= data.Remaining());

   auto &[mT0, mT1, _, mTime] = *mTimesAndSpeed;
   const bool backwards = (mT1 < mT0);
   // TODO: more-than-two-channels
   const auto maxChannels = mMaxChannels = data.Channels();
   const auto limit = std::min<size_t>(mnChannels, maxChannels);
   size_t maxTrack = 0;
   const auto mixed = stackAllocate(size_t, maxChannels);
   const auto pFloats = stackAllocate(float *, limit);
   for (size_t j = 0; j < limit; ++j)
      pFloats[j] = &data.GetWritePosition(j);
   const auto rate = GetSequence().GetRate();
   auto result = (mResampleParameters.mVariableRates || rate != mRate)
      ? MixVariableRates(limit, bound, pFloats)
      : MixSameRate(limit, bound, pFloats);
   maxTrack = std::max(maxTrack, result);
   auto newT = mSamplePos.as_double() / rate;
   if (backwards)
      mTime = std::min(mTime, newT);
   else
      mTime = std::max(mTime, newT);
   for (size_t j = 0; j < limit; ++j) {
      mixed[j] = result;
   }
   // Another pass in case channels of a track did not produce equal numbers
   for (size_t j = 0; j < limit; ++j) {
      const auto pFloat = &data.GetWritePosition(j);
      const auto result = mixed[j];
      ZeroFill(result, maxTrack, *pFloat);
   }

   mLastProduced = maxTrack;
   assert(maxTrack <= bound);
   assert(maxTrack <= data.Remaining());
   assert(maxTrack <= Remaining());
   assert(data.Remaining() > 0);
   assert(bound == 0 || Remaining() == 0 || maxTrack > 0);
   return { mLastProduced };
}

// Does not return a strictly decreasing sequence of values such as to
// provide proof of termination.  Just an indication of whether done or not.