DIrectSound on top of openAL ?

[Darragh Bailey]

On Tue, Oct 28, 2008 at 02:16:12PM -0700, Chris Robinson wrote:
> It's not very easy to get DirectSound working on top of OpenAL. I actually 
> made a DSound->OpenAL wrapper (as a native C++ Win32 DLL, so it can't go into 
> Wine as-is even if I wanted it to), but it's none too stable. Some apps work, 
> others don't. Some work better than others.
> 
> The biggest problem is updating the sound buffer in real-time (DSound lets you 
> lock a sound buffer and modify it while it's playing; OpenAL only lets you 
> rebuffer the whole buffer, while it's not attached to any source). I get 
> around this by spawning a real-time thread which queues small chunks "just in 
> time" to keep the buffer playing, but this is a hack at best.. there's no way 
> to know how much you need to buffer ahead so OpenAL doesn't run out during an 
> update, some apps are more sensitive to a large write-ahead, and real-time 
> threads aren't really available in Wine (meaning even larger sections would 
> need to be queued to be able to update in time). The problem is compounded 
> when you consider multiple DSound buffers can share the same data buffer.
> 
> Another problem is the lack of panning. OpenAL has no controls for panning a 
> 2D sound. At most you can move the sound left and right to simulate panning 
> (for mono sources; stereo is out of luck), but the actual algorithms are 
> implementation dependant and thus would not produce consistant results.
> 
> Additionally, OpenAL hides a lot of the hardware vs. software caps. OpenAL 
> doesn't tell you if you're using hardware or software, while DSound would 
> tell you. Of course you can always lie and say you have hardware (which I 
> found was needed to get some games to even attempt to use DSound3D), but it's 
> not entirely proper.


Just out of curiousity, have any of these limitations been raised with the 
OpenAL developers? Any of them in its future wish list?

If OpenAL was updated with the next release 1.2+ to support the type of
access that wine needs to support the windows sound API's on linux,
would it make it easier that supporting multiple sound drivers?

1.0 was released 2000, 1.1 in 2005, so it's probably due a new release
in the next year/two, so it might be possible to add some feature
requests that would make implementing DirectSound on top of OpenAL
visible in the future.

-- 
Darragh

"Nothing is foolproof to a sufficiently talented fool."