Function GetSourceOffset

3rdparty/openal/al/source.cpp:282–374

GetSourceOffset * * Gets the current read offset for the given Source, in the appropriate format * (Bytes, Samples or Seconds). The offset is relative to the start of the * queue (not the start of the current buffer). */

 * queue (not the start of the current buffer).
 */
ALdouble GetSourceOffset(ALsource *Source, ALenum name, ALCcontext *context)
{
    ALCdevice *device{context->mDevice.get()};
    const ALbufferlistitem *Current;
    ALuint readPos;
    ALuint readPosFrac;
    ALuint refcount;
    ALvoice *voice;

    do {
        Current = nullptr;
        readPos = readPosFrac = 0;
        while(((refcount=device->MixCount.load(std::memory_order_acquire))&1))
            std::this_thread::yield();
        voice = GetSourceVoice(Source, context);
        if(voice)
        {
            Current = voice->mCurrentBuffer.load(std::memory_order_relaxed);

            readPos = voice->mPosition.load(std::memory_order_relaxed);
            readPosFrac = voice->mPositionFrac.load(std::memory_order_relaxed);
        }
        std::atomic_thread_fence(std::memory_order_acquire);
    } while(refcount != device->MixCount.load(std::memory_order_relaxed));

    ALdouble offset{0.0};
    if(!voice) return offset;

    const ALbufferlistitem *BufferList{Source->queue};
    const ALbuffer *BufferFmt{nullptr};
    ALuint totalBufferLen{0u};
    bool readFin{false};

    while(BufferList)
    {
        if(!BufferFmt) BufferFmt = BufferList->mBuffer;

        readFin |= (BufferList == Current);
        totalBufferLen += BufferList->mSampleLen;
        if(!readFin) readPos += BufferList->mSampleLen;

        BufferList = BufferList->mNext.load(std::memory_order_relaxed);
    }
    assert(BufferFmt != nullptr);

    if(Source->Looping)
        readPos %= totalBufferLen;
    else
    {
        /* Wrap back to 0 */
        if(readPos >= totalBufferLen)
            readPos = readPosFrac = 0;
    }

    switch(name)
    {
    case AL_SEC_OFFSET:
        offset = (readPos + static_cast<ALdouble>(readPosFrac)/FRACTIONONE) / BufferFmt->Frequency;