Stay awhile and listen

A couple of days ago, I pushed to Github the first implementation for a new audio subsystem with the intention of providing a set of tools for audio playback, both in 2D and 3D.

Although Crimild does currently provide a simple 3D audio tool, it is far from useful in productive environments, specially because it lacks of any means to play audio streams, as in music.

Decided to work from scratch in the new system, I managed to complete a working version in just a couple of days and it has already proven to be much more useful than the previous one.

Here’s a brief introduction of what I’ve accomplished so far.

Core abstraction

As with many other systems in Crimild, the new new audio subsystem is split into two parts: the core abstraction and a platform dependent implementation.

A handful of new classes have been added to the core library, describing abstract interfaces for audio-related concepts, like audio sources, listeners and the audio manager itself, which also acts as an abstract factory for those objects (something that I’m planning to replicate for images too in the future).

In addition, two new components are now available: one for audio sources and the other for the audio listener (usually attached to a camera). These components will handle audio spatialization if needed (for 3D audio), using the parent node’s transformation.

But how useful is an audio system that doesn’t play audio, right?

SFML

As I was looking for a simple, portable, library that will allow me to implement the actual audio layer in a simple way, I came upon SFML. SFML is an abstraction layer for most of the platform specific functionalities, like window handling, networking and, of course, audio.

SFML provides an API to handle both 2D and 3D sounds and streams, so the implementation was pretty straightforward. Much as with other third-party dependencies (like GLFW), this code is organized in a separate package.

Integration

The unique instance for the Audio Manager is stored by the Simulation class itself, in a similar way as with the graphics renderer or other manager. The GLSimulation class, the one used in desktop projects, is already creating a valid instance upon construction, which means client projects should be able to use the new audio facilities right out of the box. No additional setup is needed.

Finally, In order to avoid confusion, I removed the old OpenAL implementation completely.

Examples

There are two examples that make use of the new audio system.

AudioRoom presents you with three music instruments in the floor. As you approach them, a music clip is played and it is possible to have more than one instrument at the same time if you move the camera quick enough.

Screen Shot 2017-11-05 at 6.43.45 PM

The Drone example has been enhanced with multiple actors. This example uses several audio sources and a listener attached to the camera to showcase how 3D sound spatialization works.

Screen Shot 2017-11-05 at 6.43.33 PM

Both of the examples are already available in the demo project.

Final comments

The new audio system is already available in the development branch, in Github. I’m still working on this code, so expect changes in the near future.

Now, I have to admit that I’m not 100% comfortable with SFML. Don’t get me wrong, the library is great and extremely useful, but it feels a bit overkill in my case. SFML provides so much functionality, not only for audio, yet I’m only using a minimal part of it, mainly because Crimild already depends on GLFW for window and input management. On the other hand, I haven’t check how to use SFML on iOS yet and that might cause some headaches in the future. Also, there’s no support for MP3 at the moment.

But then again, SFML is extremely simple to use and I’m short of time at the moment, so I guess it’s a good compromise. I’m confident that I would be able to easily change the implementation in the future if needed, since the level of abstraction of the core classes is quite good.

Time will tell.

 

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