[openal] source directivity

[Chris Robinson]

On 03/31/2016 05:58 AM, Anders Genell wrote:
> Dear list!
>
> I was wondering if there are any examples of how source directivity is
> handeled in OpenAL-soft?
> I found something about cone outer angle and inner angle and rolloff and
> source direction, but I cant figure out how that would translate to a polar
> diagram of a directivity measurement from a sournd source.

I do remember seeing an illustration of how the source cone works, 
somewhere, although I can't find it (it doesn't seem to be in the spec 
or programmer's guide).

But the general gist of it is that the cone defines areas for how sound 
is attenuated based on direction. Kind of like a spotlight. An angle 
value of 180 means it covers -90 to +90 degrees (a 180-degree area), 
where the source's direction is considered to be 0 degrees.

Given the listener's position relative to the source's position, if the 
angle between the front of the source and the direction to the listener 
is within the inner cone, the source does not apply any extra 
attenuation. If the angle is outside of the outer cone, the source 
applies extra gain given the AL_OUTER_CONE_GAIN property. If it's 
between the inner and outer cones, the amount applied is scaled as 
appropriate.

The rolloff property is separate, affecting the distance-based 
attenuation, and isn't related to the cones.