web-audio-api 0.14.0

use crate::context::{AsBaseAudioContext, AudioContextRegistration, AudioParamId};
use crate::control::Scheduler;
use crate::param::{AudioParam, AudioParamOptions, AutomationRate};
use crate::render::{AudioParamValues, AudioProcessor, AudioRenderQuantum};
use crate::{SampleRate, RENDER_QUANTUM_SIZE};

use super::{AudioNode, AudioScheduledSourceNode, ChannelConfig, ChannelConfigOptions};

/// Options for constructing an ConstantSourceNode
pub struct ConstantSourceOptions {
    pub offset: f32,
    pub channel_config: ChannelConfigOptions,
}

impl Default for ConstantSourceOptions {
    fn default() -> Self {
        Self {
            offset: 1.,
            channel_config: ChannelConfigOptions::default(),
        }
    }
}

/// Audio source whose output is nominally a constant value. A `ConstantSourceNode`
/// can be used as a constructible `AudioParam` by automating the value of its offset.
///
/// - MDN documentation: <https://developer.mozilla.org/en-US/docs/Web/API/ConstantSourceNode>
/// - specification: <https://webaudio.github.io/web-audio-api/#ConstantSourceNode>
/// - see also: [`AsBaseAudioContext::create_constant_source`](crate::context::AsBaseAudioContext::create_constant_source)
///
/// # Usage
///
/// ```no_run
/// use web_audio_api::context::{AsBaseAudioContext, AudioContext};
/// use web_audio_api::node::AudioNode;
///
/// let audio_context = AudioContext::new(None);
///
/// let gain1 = audio_context.create_gain();
/// gain1.gain().set_value(0.);
///
/// let gain2 = audio_context.create_gain();
/// gain2.gain().set_value(0.);
///
/// let automation = audio_context.create_constant_source();
/// automation.offset().set_value(0.);
/// automation.connect(gain1.gain());
/// automation.connect(gain2.gain());
///
/// // control both `GainNode`s with 1 automation
/// automation.offset().set_target_at_time(1., audio_context.current_time(), 0.1);
/// ```
///
/// # Example
///
/// - `cargo run --release --example constant_source`
///
pub struct ConstantSourceNode {
    registration: AudioContextRegistration,
    channel_config: ChannelConfig,
    offset: AudioParam,
    scheduler: Scheduler,
}

impl AudioNode for ConstantSourceNode {
    fn registration(&self) -> &AudioContextRegistration {
        &self.registration
    }

    fn channel_config_raw(&self) -> &ChannelConfig {
        &self.channel_config
    }

    fn number_of_inputs(&self) -> u32 {
        0
    }
    fn number_of_outputs(&self) -> u32 {
        1
    }
}

impl AudioScheduledSourceNode for ConstantSourceNode {
    fn scheduler(&self) -> &Scheduler {
        &self.scheduler
    }
}

impl ConstantSourceNode {
    pub fn new<C: AsBaseAudioContext>(context: &C, options: ConstantSourceOptions) -> Self {
        context.base().register(move |registration| {
            let param_opts = AudioParamOptions {
                min_value: f32::MIN,
                max_value: f32::MAX,
                default_value: 1.,
                automation_rate: AutomationRate::A,
            };
            let (param, proc) = context
                .base()
                .create_audio_param(param_opts, registration.id());
            param.set_value(options.offset);

            let scheduler = Scheduler::new();

            let render = ConstantSourceRenderer {
                offset: proc,
                scheduler: scheduler.clone(),
            };

            let node = ConstantSourceNode {
                registration,
                channel_config: options.channel_config.into(),
                offset: param,
                scheduler,
            };

            (node, Box::new(render))
        })
    }

    pub fn offset(&self) -> &AudioParam {
        &self.offset
    }
}

struct ConstantSourceRenderer {
    offset: AudioParamId,
    scheduler: Scheduler,
}

impl AudioProcessor for ConstantSourceRenderer {
    fn process(
        &mut self,
        _inputs: &[AudioRenderQuantum],
        outputs: &mut [AudioRenderQuantum],
        params: AudioParamValues,
        timestamp: f64,
        sample_rate: SampleRate,
    ) -> bool {
        // single output node
        let output = &mut outputs[0];

        let dt = 1. / sample_rate.0 as f64;
        let next_block_time = timestamp + dt * RENDER_QUANTUM_SIZE as f64;

        let start_time = self.scheduler.get_start_at();
        let stop_time = self.scheduler.get_stop_at();

        if start_time >= next_block_time {
            output.make_silent();
            return true;
        }

        if stop_time < timestamp {
            output.make_silent();
            return false;
        }

        output.force_mono();

        let offset_values = params.get(&self.offset);
        let output_channel = output.channel_data_mut(0);
        let mut current_time = timestamp;

        for (index, sample_value) in offset_values.iter().enumerate() {
            if current_time < start_time || current_time >= stop_time {
                output_channel[index] = 0.;
            } else {
                // as we pick values directly from the offset param which is already
                // computed at sub-sample accuracy, we don't need to do anything
                // special here more than copy the value to its right place.
                output_channel[index] = *sample_value;
            }

            current_time += dt;
        }

        true
    }
}

#[cfg(test)]
mod tests {
    use crate::context::{AsBaseAudioContext, OfflineAudioContext};
    use crate::node::{AudioNode, AudioScheduledSourceNode};
    use crate::SampleRate;

    use float_eq::assert_float_eq;

    #[test]
    fn test_start_stop() {
        let start_in_samples = (128 + 1) as f64; // start rendering in 2d block
        let stop_in_samples = (256 + 1) as f64; // stop rendering of 3rd block
        let mut context = OfflineAudioContext::new(1, 128 * 4, SampleRate(128));

        let src = context.create_constant_source();
        src.connect(&context.destination());

        src.start_at(start_in_samples / 128.);
        src.stop_at(stop_in_samples / 128.);

        let buffer = context.start_rendering();
        let channel = buffer.get_channel_data(0);

        // 1rst block should be silence
        assert_float_eq!(channel[0..128], vec![0.; 128][..], abs_all <= 0.);

        // 2d block - start at second frame
        let mut res = vec![1.; 128];
        res[0] = 0.;
        assert_float_eq!(channel[128..256], res[..], abs_all <= 0.);

        // 3rd block - stop at second frame
        let mut res = vec![0.; 128];
        res[0] = 1.;
        assert_float_eq!(channel[256..384], res[..], abs_all <= 0.);

        // 4th block is silence
        assert_float_eq!(channel[384..512], vec![0.; 128][..], abs_all <= 0.);
    }
}