270 lines
8.8 KiB
Rust
270 lines
8.8 KiB
Rust
use std::mem;
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use std::os::raw::c_void;
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use std::slice::from_raw_parts;
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use std::sync::Mutex;
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use stdweb;
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use stdweb::Reference;
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use stdweb::unstable::TryInto;
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use stdweb::web::TypedArray;
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use stdweb::web::set_timeout;
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use CreationError;
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use DefaultFormatError;
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use Format;
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use SupportedFormatsError;
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use StreamData;
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use SupportedFormat;
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use UnknownTypeOutputBuffer;
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// The emscripten backend works by having a global variable named `_cpal_audio_contexts`, which
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// is an array of `AudioContext` objects. A stream ID corresponds to an entry in this array.
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//
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// Creating a stream creates a new `AudioContext`. Destroying a stream destroys it.
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// TODO: handle latency better ; right now we just use setInterval with the amount of sound data
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// that is in each buffer ; this is obviously bad, and also the schedule is too tight and there may
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// be underflows
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pub struct EventLoop {
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streams: Mutex<Vec<Option<Reference>>>,
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}
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impl EventLoop {
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#[inline]
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pub fn new() -> EventLoop {
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stdweb::initialize();
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EventLoop { streams: Mutex::new(Vec::new()) }
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}
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#[inline]
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pub fn run<F>(&self, callback: F) -> !
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where F: FnMut(StreamId, StreamData)
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{
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// The `run` function uses `set_timeout` to invoke a Rust callback repeatidely. The job
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// of this callback is to fill the content of the audio buffers.
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// The first argument of the callback function (a `void*`) is a casted pointer to `self`
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// and to the `callback` parameter that was passed to `run`.
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fn callback_fn<F>(user_data_ptr: *mut c_void)
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where F: FnMut(StreamId, StreamData)
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{
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unsafe {
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let user_data_ptr2 = user_data_ptr as *mut (&EventLoop, F);
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let user_data = &mut *user_data_ptr2;
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let user_cb = &mut user_data.1;
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let streams = user_data.0.streams.lock().unwrap().clone();
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for (stream_id, stream) in streams.iter().enumerate() {
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let stream = match stream.as_ref() {
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Some(v) => v,
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None => continue,
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};
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let mut temporary_buffer = vec![0.0; 44100 * 2 / 3];
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{
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let buffer = UnknownTypeOutputBuffer::F32(::OutputBuffer { buffer: &mut temporary_buffer });
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let data = StreamData::Output { buffer: buffer };
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user_cb(StreamId(stream_id), data);
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// TODO: directly use a TypedArray<f32> once this is supported by stdweb
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}
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let typed_array = {
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let f32_slice = temporary_buffer.as_slice();
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let u8_slice: &[u8] = unsafe {
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from_raw_parts(f32_slice.as_ptr() as *const _,
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f32_slice.len() * mem::size_of::<f32>())
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};
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let typed_array: TypedArray<u8> = u8_slice.into();
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typed_array
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};
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let num_channels = 2u32; // TODO: correct value
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debug_assert_eq!(temporary_buffer.len() % num_channels as usize, 0);
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js!(
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var src_buffer = new Float32Array(@{typed_array}.buffer);
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var context = @{stream};
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var buf_len = @{temporary_buffer.len() as u32};
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var num_channels = @{num_channels};
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var buffer = context.createBuffer(num_channels, buf_len / num_channels, 44100);
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for (var channel = 0; channel < num_channels; ++channel) {
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var buffer_content = buffer.getChannelData(channel);
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for (var i = 0; i < buf_len / num_channels; ++i) {
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buffer_content[i] = src_buffer[i * num_channels + channel];
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}
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}
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var node = context.createBufferSource();
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node.buffer = buffer;
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node.connect(context.destination);
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node.start();
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);
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}
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set_timeout(|| callback_fn::<F>(user_data_ptr), 330);
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}
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}
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let mut user_data = (self, callback);
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let user_data_ptr = &mut user_data as *mut (_, _);
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set_timeout(|| callback_fn::<F>(user_data_ptr as *mut _), 10);
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stdweb::event_loop();
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}
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#[inline]
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pub fn build_input_stream(&self, _: &Device, _format: &Format) -> Result<StreamId, CreationError> {
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unimplemented!();
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}
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#[inline]
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pub fn build_output_stream(&self, _: &Device, _format: &Format) -> Result<StreamId, CreationError> {
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let stream = js!(return new AudioContext()).into_reference().unwrap();
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let mut streams = self.streams.lock().unwrap();
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let stream_id = if let Some(pos) = streams.iter().position(|v| v.is_none()) {
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streams[pos] = Some(stream);
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pos
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} else {
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let l = streams.len();
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streams.push(Some(stream));
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l
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};
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Ok(StreamId(stream_id))
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}
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#[inline]
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pub fn destroy_stream(&self, stream_id: StreamId) {
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self.streams.lock().unwrap()[stream_id.0] = None;
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}
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#[inline]
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pub fn play_stream(&self, stream_id: StreamId) {
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let streams = self.streams.lock().unwrap();
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let stream = streams
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.get(stream_id.0)
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.and_then(|v| v.as_ref())
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.expect("invalid stream ID");
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js!(@{stream}.resume());
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}
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#[inline]
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pub fn pause_stream(&self, stream_id: StreamId) {
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let streams = self.streams.lock().unwrap();
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let stream = streams
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.get(stream_id.0)
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.and_then(|v| v.as_ref())
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.expect("invalid stream ID");
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js!(@{stream}.suspend());
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}
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}
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// Index within the `streams` array of the events loop.
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#[derive(Debug, Clone, PartialEq, Eq, Hash)]
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pub struct StreamId(usize);
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// Detects whether the `AudioContext` global variable is available.
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fn is_webaudio_available() -> bool {
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stdweb::initialize();
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js!(if (!AudioContext) {
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return false;
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} else {
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return true;
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}).try_into()
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.unwrap()
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}
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// Content is false if the iterator is empty.
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pub struct Devices(bool);
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impl Default for Devices {
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fn default() -> Devices {
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// We produce an empty iterator if the WebAudio API isn't available.
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Devices(is_webaudio_available())
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}
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}
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impl Iterator for Devices {
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type Item = Device;
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#[inline]
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fn next(&mut self) -> Option<Device> {
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if self.0 {
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self.0 = false;
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Some(Device)
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} else {
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None
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}
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}
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}
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#[inline]
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pub fn default_input_device() -> Option<Device> {
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unimplemented!();
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}
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#[inline]
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pub fn default_output_device() -> Option<Device> {
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if is_webaudio_available() {
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Some(Device)
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} else {
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None
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}
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}
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#[derive(Clone, Debug, PartialEq, Eq)]
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pub struct Device;
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impl Device {
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#[inline]
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pub fn name(&self) -> String {
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"Default Device".to_owned()
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}
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#[inline]
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pub fn supported_input_formats(&self) -> Result<SupportedInputFormats, SupportedFormatsError> {
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unimplemented!();
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}
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#[inline]
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pub fn supported_output_formats(&self) -> Result<SupportedOutputFormats, SupportedFormatsError> {
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// TODO: right now cpal's API doesn't allow flexibility here
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// "44100" and "2" (channels) have also been hard-coded in the rest of the code ; if
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// this ever becomes more flexible, don't forget to change that
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// According to https://developer.mozilla.org/en-US/docs/Web/API/BaseAudioContext/createBuffer
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// browsers must support 1 to 32 channels at leats and 8,000 Hz to 96,000 Hz.
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Ok(
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vec![
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SupportedFormat {
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channels: 2,
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min_sample_rate: ::SampleRate(44100),
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max_sample_rate: ::SampleRate(44100),
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data_type: ::SampleFormat::F32,
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},
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].into_iter(),
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)
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}
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pub fn default_input_format(&self) -> Result<Format, DefaultFormatError> {
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unimplemented!();
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}
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pub fn default_output_format(&self) -> Result<Format, DefaultFormatError> {
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// TODO: because it is hard coded, see supported_output_formats.
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Ok(
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Format {
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channels: 2,
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sample_rate: ::SampleRate(44100),
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data_type: ::SampleFormat::F32,
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},
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)
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}
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}
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pub type SupportedInputFormats = ::std::vec::IntoIter<SupportedFormat>;
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pub type SupportedOutputFormats = ::std::vec::IntoIter<SupportedFormat>;
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