[Bug 28723] Sound stutter in Rage when emulated windows version is set to "Windows 7" (XAudio2 -> mmdevapi sound output path)

[wine-bugs at winehq.org]

http://bugs.winehq.org/show_bug.cgi?id=28723

--- Comment #32 from Jörg Höhle <hoehle at users.sourceforge.net> 2011-11-04 16:57:49 CDT ---
*out = This->held_frames;
Come to think of it, this is presumably what native GetCurrentPadding does in
shared mode and what Wine should do. Native's shared mode GCP means the buffer
is that much free, and the rest was sent to the mixer -- it does not mean that
the rest was already "consumed" by the HW.

There are 2 issues, though:
1. Native mixes 10ms and sends them to the HW, whereas Wine has all of the ALSA
buffer in front of it. As you experienced in comment #24, this adds latency as
large as ALSA's buffer.

2. GetPosition in Wine is based on GetCurrentPadding. I wrote in
http://www.winehq.org/pipermail/wine-devel/2011-August/091562.html
that this is bogus, snd_pcm_delay must be used instead but I've not polished
the patch since.
With a fixed GetPosition, the modified GCP would pass my render.c tests.

Point 1. can be improved by calling snd_pcm_hw_params_set_buffer_time_max when
duration is small (perhaps < 50ms?), revealing that the app wants tight timing.
The final word has not been said yet on snd_pcm_set_period/buffer_min/max/near.
I've not yet found an interesting formula and a good heuristic to distinguish 2
use cases: "size doesn't matter, just play" and "low-latency shooter reaction".

Something else to prevent underruns may be to pretend running at 10ms like
native, but use a period of 5ms.  This would hopefully account for the fact
that ALSA's buffer filling need is not synchronized with mmdevapi's timer. Then
again, try and find an heuristic not to always run at 5ms (e.g. PlaySound
doesn't need that).

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