# Rust bindings for Oboe library

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Safe Rust interface for [Oboe](https://github.com/google/oboe) High-Performance Audio library for Android.
Also it provides interface for some platform APIs significant to Audio IO.

__Oboe__ is a C++ library which makes it easy to build high-performance audio apps on Android. It was created primarily to allow developers to target a simplified API that works across multiple API levels back to API level 16 (Jelly Bean).

## Crate features

- __java-interface__ Add interface for some Android platform APIs.
- __generate-bindings__ Generate bindings at compile-time. By default the pregenerated bindings will be used.
- __compile-library__ Compile _oboe_ C++ library at compile-time using __cmake__. By default the precompiled library will be used.
- __shared-link__ Use shared linking. By default the static Oboe libarary will be used.

The crate already has pregenerated bindings and precompiled static libraries for the following Android targets:

- __armv7__
- __aarch64__
- __i686__
- __x86_64__

## Build issues

The **[clang-sys](https://crates.io/crates/clang-sys)** crate uses **[llvm-config](http://llvm.org/docs/CommandGuide/llvm-config.html)** for searching [libclang](https://clang.llvm.org/docs/Tooling.html) library and preparing _C_/_C++_ compiler configuration. In order to get proper setup you should add *llvm-config* to your executables search path.

In case of using tools with libclang under the hood like __bindgen__ you must be sure in proper your setup. Otherwise you get an errors related to missing headers or definitions.

To build applications you need recent version of __cargo-apk__, which supports latest Android [SDK](https://developer.android.com/studio#command-tools) (28+) and [NDK](https://developer.android.com/ndk) (20+). Don't forget to set ANDROID_SDK_ROOT environment variable with paths to installed SDK.

For building host crates which requires C-compiler you may also set __HOST_CC__ environment variable with path to your C-compiler.

## Usage example

Playing sine wave in asynchronous (callback-driven) mode:

```rust
use oboe::{
    AudioOutputCallback,
    AudioOutputStream,
    AudioStreamBuilder,
    DataCallbackResult,
    PerformanceMode,
    SharingMode,
    Mono,
};

// Structure for sound generator
pub struct SineWave {
    frequency: f32,
    gain: f32,
    phase: f32,
    delta: Option<f32>,
}

// Default constructor for sound generator
impl Default for SineWave {
    fn default() -> Self {
        Self {
            frequency: 440.0,
            gain: 0.5,
            phase: 0.0,
            delta: None,
        }
    }
}

// Audio output callback trait implementation
impl AudioOutputCallback for SineWave {
    // Define type for frames which we would like to process
    type FrameType = (f32, Mono);

    // Implement sound data output callback
    fn on_audio_ready(&mut self, stream: &mut dyn AudioOutputStream, frames: &mut [f32]) -> DataCallbackResult {
        // Configure out wave generator
        if self.delta.is_none() {
            let sample_rate = stream.get_sample_rate() as f32;
            self.delta = (self.frequency * 2.0 * PI / sample_rate).into();
            println!("Prepare sine wave generator: samplerate={}, time delta={}", sample_rate, self.delta.unwrap());
        }

        let delta = self.delta.unwrap();

        // Generate audio frames to fill the output buffer
        for frame in frames {
            *frame = self.gain * self.phase.sin();
            self.phase += delta;
            while self.phase > 2.0 * PI {
                self.phase -= 2.0 * PI;
            }
        }

        // Notify the oboe that stream is continued
        DataCallbackResult::Continue
    }
}

// ...

// Create playback stream
let mut sine = AudioStreamBuilder::default()
    // select desired performance mode
    .set_performance_mode(PerformanceMode::LowLatency)
    // select desired sharing mode
    .set_sharing_mode(SharingMode::Shared)
    // select sound sample format
    .set_format::<f32>()
    // select channels configuration
    .set_channel_count::<Mono>()
    // set our generator as callback
    .set_callback(SineWave::default())
    // open the output stream
    .open_stream()
    .unwrap();

// Start playback
sine.start().unwrap();

// ...
```
