[openal] Extending max source gain

[Chris Robinson]

On 08/10/2016 10:50 AM, Ethan Lee wrote:
> My only real concern is the possibility of breaking existing behavior
> for older applications. That would only ever apply if AL_MAX_GAIN's
> default was changed, but as long as that remains at 1.0f then we can
> just allow up to FLT_MAX and not affect existing code.

Yes, the default would remain 1.0f for compatibility. This would just 
increase the range it's allowed to be set to.

> Something like an
> alGetFloat(AL_MAX_GAIN_LIMIT_SOFT) would work for us in FNA, though that
> kind of limitation may as well apply to AL_MIN_GAIN too since we're
> thinking about MAX.

Note that the queried max limit would be the implicit clamping level an 
implementation may do after the final volume is calculated, not strictly 
how high the source's AL_MAX_GAIN property can go. I don't imagine an 
implementation will have a minimum volume clamp like it may have a 
maximum volume clamp. I suppose there could be a query for the minimum 
non-0 volume before it just skips rendering and goes silent, though I 
don't know how useful that would be.