[openal] Enabling HRTF

[Chris Robinson]

On 12/05/2014 01:33 AM, Richard Furse wrote:
> Interesting.
>
> Rapture3D currently handles this by allowing the HRTF to be changed
> in an external GUI while the game is running. This avoids the game
> having to add menus itself, but is a bit clunky.
>
> Beyond that, we've wondered about adding some options to
> alcCreateContext(). I'm not familiar with alcDeviceReset().

alcDeviceReset is just a conceptual thing in my mind right now. It would 
be a way for the app to specify new device parameters, such as 
ALC_FREQUENCY, ALC_HRTF, etc, without having to create a new context 
with alcCreateContext. All existing sources and auxiliary slots and 
stuff remain valid, they'd retain their property values and state, and 
so on.

Internally, I imagine it to work basically by stopping the playback 
device temporarily, update the device parameters according to given the 
attributes, update the source and auxiliary slot mixing parameters as 
needed, then restart device playback. Any sources that were playing 
before the call keep playing afterward.