From 002db0d9ff4d29b3609afdd60c333ba5e19b1954 Mon Sep 17 00:00:00 2001 From: rossb Date: Thu, 10 Nov 2011 08:34:00 +0000 Subject: [PATCH] added comments explaining why ticket #199 can't be fixed --- src/hostapi/asio/pa_asio.cpp | 28 ++++++++++++++++++++++++---- 1 file changed, 24 insertions(+), 4 deletions(-) diff --git a/src/hostapi/asio/pa_asio.cpp b/src/hostapi/asio/pa_asio.cpp index 8c78bf2..281cfcc 100644 --- a/src/hostapi/asio/pa_asio.cpp +++ b/src/hostapi/asio/pa_asio.cpp @@ -2238,10 +2238,29 @@ static PaError OpenStream( struct PaUtilHostApiRepresentation *hostApi, } else /* Using callback interface... */ { - framesPerHostBuffer = SelectHostBufferSize( + /* Select the host buffer size based on user framesPerBuffer and the + maximum of suggestedInputLatencyFrames and + suggestedOutputLatencyFrames. + + We should subtract any fixed known driver latency from + suggestedLatencyFrames before computing the host buffer size. + However, the ASIO API doesn't provide a method for determining fixed + latencies independent of the host buffer size. ASIOGetLatencies() + only returns latencies after the buffer size has been configured, so + we can't reliably use it to determine fixed latencies here. + + We could set the preferred buffer size and then subtract it from + the values returned from ASIOGetLatencies, but this would not be 100% + reliable, so we don't do it. + */ + + unsigned long suggestedLatencyFrames = (( suggestedInputLatencyFrames > suggestedOutputLatencyFrames ) - ? suggestedInputLatencyFrames : suggestedOutputLatencyFrames), framesPerBuffer, - driverInfo ); + ? suggestedInputLatencyFrames + : suggestedOutputLatencyFrames); + + framesPerHostBuffer = SelectHostBufferSize( suggestedLatencyFrames, + framesPerBuffer, driverInfo ); } @@ -2391,7 +2410,8 @@ static PaError OpenStream( struct PaUtilHostApiRepresentation *hostApi, stream->outputBufferConverter = 0; } - + /* Values returned by ASIOGetLatencies() include the latency introduced by + the ASIO double buffer. */ ASIOGetLatencies( &stream->asioInputLatencyFrames, &stream->asioOutputLatencyFrames ); -- 2.43.0