Re: Two more questions

On 11/16/2012 10:22 AM, [email protected] wrote:
>> Yes, this is the right list for those type of questions.
>>
>> There's also the openal-devel list for questions about the internals of
>> OpenAL itself.
>>
>> --"J"
>>
> Oh, good.  Thank you.  Now, prepared to be driven bananas by all my
> questions.
>
> Let me first introduce my project.  I'm working with JMRI, which is a
> software suite for doing computer-related things with model trains.  So my
> application is a little bit different from the usual gaming application of
> OpenAL, but it seems to be working well so far.
>
> My part is called "Virtual Sound Decoder", or "VSD" for short.  What it
> does is keep track of a model train's position and speed, and plays train
> sounds (engine rumble, bell, whistle, horn, etc.) in response to the train
> engineer's throttle inputs.  I have a video demo of an early prototype of
> the code on YouTube here: http://www.youtube.com/watch?v=-Tgzz72Y0ao
>
> First up, I have read the Programmer's Guide, but I'd like to make sure I
> understand it correctly.
>
> Let's say I have a PC, and it has a sound card.  That's one Device, right?

Yes, for the most part (some fancy hardware might end up having multiple 
"devices", but you probably won't need to worry about that)


> That one Device.  Can I have two, or three, or twenty Contexts opened up
> on that same Device?

In theory yes.  That's probably one of the less-used features of OpenAL, 
so you may run into issues, but it's supposed to work the way you describe.


> Can those Contexts be in different modes (one in Stereo, another in 5.1
> Surround)?  Does the answer depend on the capabilities of the device?

"It depends" is probably the best answer.  Mainly, it will depend on the 
capabilities of the back-end audio system that you're using (MMSYSTEM, 
DirectSound, WASAPI, ALSA, Pulse, etc.).  Chris could probably answer 
this point better than me, though.


> The reason for this question is that there are other parts of JMRI that
> also generate sounds (things like ambient noises, control panel beeps and
> clicks, and so on), and I would like to know how much independence VSD can
> have in controlling its own Context vs. having to share with the other
> sound-generating parts of JMRI.

I'd plan on dealing with a common mixing format between all contexts, if 
possible.  It will probably avoid some headaches.


>
> There can be only one Listener per Context. That seems clear.

Correct

> Do I understand correctly that Sources cannot be shared... i.e. if I want
> to play the same buffer in two different Contexts, I have to have a
> separate Source in each Context, with those two (or more) Sources linked
> to the same Buffer, right?

Sources are per-context, from what I remember, so yes, you'd have to 
duplicate any sources that you'd want to appear in multiple contexts


> Thanks a bunch!  OpenAL is very cool, and is really helping me turn this
> into something fun.

Sounds like a fun project.  Good luck!

--"J"

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