pa_process.c

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            *streamCallbackResult = bp->streamCallback( userInput, userOutput,
                    bp->framesPerUserBuffer, bp->timeInfo,
                    bp->callbackStatusFlags, bp->userData );

            if( *streamCallbackResult == paAbort )
            {
                /* if the callback returned paAbort, we disregard its output */
            }
            else
            {
                bp->timeInfo->outputBufferDacTime += bp->framesPerUserBuffer * bp->samplePeriod;

                bp->framesInTempOutputBuffer = bp->framesPerUserBuffer;
            }
        }

        if( bp->framesInTempOutputBuffer > 0 )
        {
            /* convert frameCount frames from user buffer to host buffer */

            frameCount = PA_MIN_( bp->framesInTempOutputBuffer, framesToGo );

            if( bp->userOutputIsInterleaved )
            {
                srcBytePtr = ((unsigned char*)bp->tempOutputBuffer) +
                        bp->bytesPerUserOutputSample * bp->outputChannelCount *
                        (bp->framesPerUserBuffer - bp->framesInTempOutputBuffer);

                srcSampleStrideSamples = bp->outputChannelCount;
                srcChannelStrideBytes = bp->bytesPerUserOutputSample;
            }
            else /* user output is not interleaved */
            {
                srcBytePtr = ((unsigned char*)bp->tempOutputBuffer) +
                        bp->bytesPerUserOutputSample *
                        (bp->framesPerUserBuffer - bp->framesInTempOutputBuffer);
                            
                srcSampleStrideSamples = 1;
                srcChannelStrideBytes = bp->framesPerUserBuffer * bp->bytesPerUserOutputSample;
            }

            for( i=0; i<bp->outputChannelCount; ++i )
            {
                bp->outputConverter(    hostOutputChannels[i].data,
                                        hostOutputChannels[i].stride,
                                        srcBytePtr, srcSampleStrideSamples,
                                        frameCount, &bp->ditherGenerator );

                srcBytePtr += srcChannelStrideBytes;  /* skip to next source channel */

                /* advance dest ptr for next iteration */
                hostOutputChannels[i].data = ((unsigned char*)hostOutputChannels[i].data) +
                        frameCount * hostOutputChannels[i].stride * bp->bytesPerHostOutputSample;
            }

            bp->framesInTempOutputBuffer -= frameCount;
        }
        else
        {
            /* no more user data is available because the callback has returned
                paComplete or paAbort. Fill the remainder of the host buffer
                with zeros.
            */

            frameCount = framesToGo;

            for( i=0; i<bp->outputChannelCount; ++i )
            {
                bp->outputZeroer(   hostOutputChannels[i].data,
                                    hostOutputChannels[i].stride,
                                    frameCount );

                /* advance dest ptr for next iteration */
                hostOutputChannels[i].data = ((unsigned char*)hostOutputChannels[i].data) +
                        frameCount * hostOutputChannels[i].stride * bp->bytesPerHostOutputSample;
            }
        }
        
        framesProcessed += frameCount;
        
        framesToGo -= frameCount;

    }while( framesToGo > 0 );

    return framesProcessed;
}

/* CopyTempOutputBuffersToHostOutputBuffers is called from AdaptingProcess to copy frames from
	tempOutputBuffer to hostOutputChannels. This includes data conversion
	and interleaving. 
*/
static void CopyTempOutputBuffersToHostOutputBuffers( PaUtilBufferProcessor *bp)
{
    unsigned long maxFramesToCopy;
    PaUtilChannelDescriptor *hostOutputChannels;
    unsigned int frameCount;
    unsigned char *srcBytePtr;
    unsigned int srcSampleStrideSamples; /* stride from one sample to the next within a channel, in samples */
    unsigned int srcChannelStrideBytes; /* stride from one channel to the next, in bytes */
    unsigned int i;

     /* copy frames from user to host output buffers */
     while( bp->framesInTempOutputBuffer > 0 &&
             ((bp->hostOutputFrameCount[0] + bp->hostOutputFrameCount[1]) > 0) )
     {
         maxFramesToCopy = bp->framesInTempOutputBuffer;

         /* select the output buffer set (1st or 2nd) */
         if( bp->hostOutputFrameCount[0] > 0 )
         {
             hostOutputChannels = bp->hostOutputChannels[0];
             frameCount = PA_MIN_( bp->hostOutputFrameCount[0], maxFramesToCopy );
         }
         else
         {
             hostOutputChannels = bp->hostOutputChannels[1];
             frameCount = PA_MIN_( bp->hostOutputFrameCount[1], maxFramesToCopy );
         }

         if( bp->userOutputIsInterleaved )
         {
             srcBytePtr = ((unsigned char*)bp->tempOutputBuffer) +
                     bp->bytesPerUserOutputSample * bp->outputChannelCount *
                     (bp->framesPerUserBuffer - bp->framesInTempOutputBuffer);
                         
             srcSampleStrideSamples = bp->outputChannelCount;
             srcChannelStrideBytes = bp->bytesPerUserOutputSample;
         }
         else /* user output is not interleaved */
         {
             srcBytePtr = ((unsigned char*)bp->tempOutputBuffer) +
                     bp->bytesPerUserOutputSample *
                     (bp->framesPerUserBuffer - bp->framesInTempOutputBuffer);

             srcSampleStrideSamples = 1;
             srcChannelStrideBytes = bp->framesPerUserBuffer * bp->bytesPerUserOutputSample;
         }

         for( i=0; i<bp->outputChannelCount; ++i )
         {
             bp->outputConverter(    hostOutputChannels[i].data,
                                     hostOutputChannels[i].stride,
                                     srcBytePtr, srcSampleStrideSamples,
                                     frameCount, &bp->ditherGenerator );

             srcBytePtr += srcChannelStrideBytes;  /* skip to next source channel */

             /* advance dest ptr for next iteration */
             hostOutputChannels[i].data = ((unsigned char*)hostOutputChannels[i].data) +
                     frameCount * hostOutputChannels[i].stride * bp->bytesPerHostOutputSample;
         }

         if( bp->hostOutputFrameCount[0] > 0 )
             bp->hostOutputFrameCount[0] -= frameCount;
         else
             bp->hostOutputFrameCount[1] -= frameCount;

         bp->framesInTempOutputBuffer -= frameCount;
     }
}

/*
    AdaptingProcess is a full duplex adapting buffer processor. It converts
    data from the temporary output buffer into the host output buffers, then
    from the host input buffers into the temporary input buffers. Calling the
    streamCallback when necessary.
    When processPartialUserBuffers is 0, all available input data will be
    consumed and all available output space will be filled. When
    processPartialUserBuffers is non-zero, as many full user buffers
    as possible will be processed, but partial buffers will not be consumed.
*/
static unsigned long AdaptingProcess( PaUtilBufferProcessor *bp,
        int *streamCallbackResult, int processPartialUserBuffers )
{
    void *userInput, *userOutput;
    unsigned long framesProcessed = 0;
    unsigned long framesAvailable;
    unsigned long endProcessingMinFrameCount;
    unsigned long maxFramesToCopy;
    PaUtilChannelDescriptor *hostInputChannels, *hostOutputChannels;
    unsigned int frameCount;
    unsigned char *destBytePtr;
    unsigned int destSampleStrideSamples; /* stride from one sample to the next within a channel, in samples */
    unsigned int destChannelStrideBytes; /* stride from one channel to the next, in bytes */
    unsigned int i, j;
 

    framesAvailable = bp->hostInputFrameCount[0] + bp->hostInputFrameCount[1];/* this is assumed to be the same as the output buffer's frame count */

    if( processPartialUserBuffers )
        endProcessingMinFrameCount = 0;
    else
        endProcessingMinFrameCount = (bp->framesPerUserBuffer - 1);

    /* Fill host output with remaining frames in user output (tempOutputBuffer) */
    CopyTempOutputBuffersToHostOutputBuffers( bp );		  	

    while( framesAvailable > endProcessingMinFrameCount ) 
    {

        if( bp->framesInTempOutputBuffer == 0 && *streamCallbackResult != paContinue )
        {
            /* the callback will not be called any more, so zero what remains
                of the host output buffers */

            for( i=0; i<2; ++i )
            {
                frameCount = bp->hostOutputFrameCount[i];
                if( frameCount > 0 )
                {
                    hostOutputChannels = bp->hostOutputChannels[i];
                    
                    for( j=0; j<bp->outputChannelCount; ++j )
                    {
                        bp->outputZeroer(   hostOutputChannels[j].data,
                                            hostOutputChannels[j].stride,
                                            frameCount );

                        /* advance dest ptr for next iteration  */
                        hostOutputChannels[j].data = ((unsigned char*)hostOutputChannels[j].data) +
                                frameCount * hostOutputChannels[j].stride * bp->bytesPerHostOutputSample;
                    }
                    bp->hostOutputFrameCount[i] = 0;
                }
            }
        }          


        /* copy frames from host to user input buffers */
        while( bp->framesInTempInputBuffer < bp->framesPerUserBuffer &&
                ((bp->hostInputFrameCount[0] + bp->hostInputFrameCount[1]) > 0) )
        {
            maxFramesToCopy = bp->framesPerUserBuffer - bp->framesInTempInputBuffer;

            /* select the input buffer set (1st or 2nd) */
            if( bp->hostInputFrameCount[0] > 0 )
            {
                hostInputChannels = bp->hostInputChannels[0];
                frameCount = PA_MIN_( bp->hostInputFrameCount[0], maxFramesToCopy );
            }
            else
            {
                hostInputChannels = bp->hostInputChannels[1];
                frameCount = PA_MIN_( bp->hostInputFrameCount[1], maxFramesToCopy );
            }

            /* configure conversion destination pointers */
            if( bp->userInputIsInterleaved )
            {
                destBytePtr = ((unsigned char*)bp->tempInputBuffer) +
                        bp->bytesPerUserInputSample * bp->inputChannelCount *
                        bp->framesInTempInputBuffer;

                destSampleStrideSamples = bp->inputChannelCount;
                destChannelStrideBytes = bp->bytesPerUserInputSample;
            }
            else /* user input is not interleaved */
            {
                destBytePtr = ((unsigned char*)bp->tempInputBuffer) +
                        bp->bytesPerUserInputSample * bp->framesInTempInputBuffer;

                destSampleStrideSamples = 1;
                destChannelStrideBytes = bp->framesPerUserBuffer * bp->bytesPerUserInputSample;
            }

            for( i=0; i<bp->inputChannelCount; ++i )
            {
                bp->inputConverter( destBytePtr, destSampleStrideSamples,
                                        hostInputChannels[i].data,
                                        hostInputChannels[i].stride,
                                        frameCount, &bp->ditherGenerator );

                destBytePtr += destChannelStrideBytes;  /* skip to next destination channel */

                /* advance src ptr for next iteration */
                hostInputChannels[i].data = ((unsigned char*)hostInputChannels[i].data) +
                        frameCount * hostInputChannels[i].stride * bp->bytesPerHostInputSample;
            }

            if( bp->hostInputFrameCount[0] > 0 )
                bp->hostInputFrameCount[0] -= frameCount;
            else
                bp->hostInputFrameCount[1] -= frameCount;
                
            bp->framesInTempInputBuffer += frameCount;

            /* update framesAvailable and framesProcessed based on input consumed
                unless something is very wrong this will also correspond to the
                amount of output generated */
            framesAvailable -= frameCount;
            framesProcessed += frameCount;
        }

        /* call streamCallback */
        if( bp->framesInTempInputBuffer == bp->framesPerUserBuffer &&
            bp->framesInTempOutputBuffer == 0 )
        {
            if( *streamCallbackResult == paContinue )
            {
                /* setup userInput */
                if( bp->userInputIsInterleaved )
                {
                    userInput = bp->tempInputBuffer;
                }
                else /* user input is not interleaved */
                {
                    for( i = 0; i < bp->inputChannelCount; ++i )
                    {
                        bp->tempInputBufferPtrs[i] = ((unsigned char*)bp->tempInputBuffer) +
                                i * bp->framesPerUserBuffer * bp->bytesPerUserInputSample;
                    }

                    userInput = bp->tempInputBufferPtrs;
                }

                /* setup userOutput */
                if( bp->userOutputIsInterleaved )
                {
                    userOutput = bp->tempOutputBuffer;
                }
                else /* user output is not interleaved */
                {
                    for( i = 0; i < bp->outputChannelCount; ++i )
                    {
                        bp->tempOutputBufferPtrs[i] = ((unsigned char*)bp->tempOutputBuffer) +
                                i * bp->framesPerUserBuffer * bp->bytesPerUserOutputSample;
                    }

                    userOutput = bp->tempOutputBufferPtrs;
                }

                /* call streamCallback */

                *streamCallbackResult = bp->streamCallback( userInput, userOutput,
                        bp->framesPerUserBuffer, bp->timeInfo,
                        bp->callbackStatusFlags, bp->userData );

                bp->timeInfo->inputBufferAdcTime += bp->framesPerUserBuffer * bp->samplePeriod;
                bp->timeInfo->outputBufferDacTime += bp->framesPerUserBuffer * bp->samplePeriod;

                bp->framesInTempInputBuffer = 0;

                if( *streamCallbackResult == paAbort )
                    bp->framesInTempOutputBuffer = 0;
                else
                    bp->framesInTempOutputBuffer = bp->framesPerUserBuffer;