[openal] HRTF on Android

[Chris Robinson]

On 02/16/2017 06:34 PM, Cyril Drouet wrote:
> From what I understand, on Windows or Linux, I'm supposed to edit the
> alsoft.conf file and set hrtf to true, and specify a list of files to
> hrtf_tables.

The hrtf and hrtf_tables config options are for setting it on your 
specific system. With 1.17.2, you can set the ALSOFT_LOCAL_PATH 
environment variable before calling any OpenAL functions (really before 
HRTFs are enumerated, but that can happen implicitly by a number of 
calls so it's best to set it once ASAP). It will then search that path 
for mhr (HRTF) files when enumerating them. I don't know exactly how 
this works for "normal" Android apps, where files should be so standard 
I/O functions can access them. With the current Git version (soon 1.18), 
you can embed a couple HRTFs into the lib so they're automatically 
accessible.

The hrtf option is just to set the default behavior for using HRTF. The 
ALC_SOFT_HRTF extension is how you can enable/disable it from the app. 
Though obviously it won't help much if the lib didn't find any HRTF 
files to use.