Chris Robinson
a6a5634adb
Because floating-point math is not associative ((a*b)*c does not necessarily give the same result as a*(b*c)), the ordering of terms can inhibit reuse of temporary values. For example, both coeffs[9] = 2.091650066f * y * (3.0f*x*x - y*y); and coeffs[15] = 2.091650066f * x * (x*x - 3.0f*y*y); contain x*x and y*y terms that could be calculated once, stored in temporary registers, and reused to multiply with 3. But since 3.0f*(x*x) would produce different results, the compiler is not allowed to make that optimization. If, however, the multiply with 3 is moved to the right side: coeffs[9] = 2.091650066f * y * (x*x*3.0f - y*y); and coeffs[15] = 2.091650066f * x * (x*x - y*y*3.0f); in both cases x*x and y*y are calculated first in their respective groups, guaranteeing the same results for both instances prior to the multiply with 3 and allowing the compiler to reuse those intermediate values.
OpenAL soft
master branch CI status : 
OpenAL Soft is an LGPL-licensed, cross-platform, software implementation of the OpenAL 3D audio API. It's forked from the open-sourced Windows version available originally from openal.org's SVN repository (now defunct). OpenAL provides capabilities for playing audio in a virtual 3D environment. Distance attenuation, doppler shift, and directional sound emitters are among the features handled by the API. More advanced effects, including air absorption, occlusion, and environmental reverb, are available through the EFX extension. It also facilitates streaming audio, multi-channel buffers, and audio capture.
More information is available on the official website
Source Install
To install OpenAL Soft, use your favorite shell to go into the build/ directory, and run:
cmake ..
Assuming configuration went well, you can then build it, typically using GNU Make (KDevelop, MSVC, and others are possible depending on your system setup and CMake configuration).
Please Note: Double check that the appropriate backends were detected. Often, complaints of no sound, crashing, and missing devices can be solved by making sure the correct backends are being used. CMake's output will identify which backends were enabled.
For most systems, you will likely want to make sure ALSA, OSS, and PulseAudio were detected (if your target system uses them). For Windows, make sure DirectSound was detected.
Utilities
The source package comes with an informational utility, openal-info, and is built by default. It prints out information provided by the ALC and AL sub- systems, including discovered devices, version information, and extensions.
Configuration
OpenAL Soft can be configured on a per-user and per-system basis. This allows users and sysadmins to control information provided to applications, as well as application-agnostic behavior of the library. See alsoftrc.sample for available settings.
Acknowledgements
Special thanks go to:
- Creative Labs for the original source code this is based off of.
- Christopher Fitzgerald for the current reverb effect implementation, and helping with the low-pass and HRTF filters.
- Christian Borss for the 3D panning code previous versions used as a base.
- Ben Davis for the idea behind a previous version of the click-removal code.
- Richard Furse for helping with my understanding of Ambisonics that is used by the various parts of the library.