kira 0.12.0

Expressive audio library for games
Documentation 
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//! Removes frequencies from a sound.

mod builder;
mod handle;

pub use builder::*;
pub use handle::*;

use std::f64::consts::PI;

use crate::{
	Mix, Parameter,
	command::{ValueChangeCommand, read_commands_into_parameters},
	command_writers_and_readers,
	effect::Effect,
	frame::Frame,
	info::Info,
};

// This filter code is based on the filter code from baseplug:
// https://github.com/wrl/baseplug/blob/trunk/examples/svf/svf_simper.rs

/// The frequencies that the filter will remove.
#[derive(Debug, Copy, Clone, PartialEq)]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub enum FilterMode {
	/// Removes frequencies above the cutoff frequency.
	LowPass,
	/// Removes frequencies above and below the cutoff frequency.
	BandPass,
	/// Removes frequencies below the cutoff frequency.
	HighPass,
	/// Removes frequencies around the cutoff frequency.
	Notch,
}

struct Filter {
	command_readers: CommandReaders,
	mode: FilterMode,
	cutoff: Parameter,
	resonance: Parameter,
	mix: Parameter<Mix>,
	ic1eq: Frame,
	ic2eq: Frame,
}

impl Filter {
	/// Creates a new filter.
	#[must_use]
	fn new(builder: FilterBuilder, command_readers: CommandReaders) -> Self {
		Self {
			command_readers,
			mode: builder.mode,
			cutoff: Parameter::new(builder.cutoff, 1000.0),
			resonance: Parameter::new(builder.resonance, 0.0),
			mix: Parameter::new(builder.mix, Mix(1.0)),
			ic1eq: Frame::ZERO,
			ic2eq: Frame::ZERO,
		}
	}
}

impl Effect for Filter {
	fn on_start_processing(&mut self) {
		if let Some(mode) = self.command_readers.set_mode.read() {
			self.mode = mode;
		}
		read_commands_into_parameters!(self, cutoff, resonance, mix);
	}

	fn process(&mut self, input: &mut [Frame], dt: f64, info: &Info) {
		self.cutoff.update(dt * input.len() as f64, info);
		self.resonance.update(dt * input.len() as f64, info);
		self.mix.update(dt * input.len() as f64, info);

		let num_frames = input.len();
		for (i, frame) in input.iter_mut().enumerate() {
			let time_in_chunk = (i + 1) as f64 / num_frames as f64;
			let cutoff = self.cutoff.interpolated_value(time_in_chunk);
			let resonance = self
				.resonance
				.interpolated_value(time_in_chunk)
				.clamp(0.0, 1.0);
			let mix = self.mix.interpolated_value(time_in_chunk).0.clamp(0.0, 1.0);

			let sample_rate = 1.0 / dt;
			let g = (PI * (cutoff / sample_rate).clamp(0.0001, 0.5)).tan();
			let k = 2.0 - (1.9 * resonance);
			let a1 = 1.0 / (1.0 + (g * (g + k)));
			let a2 = g * a1;
			let a3 = g * a2;
			let v3 = *frame - self.ic2eq;
			let v1 = (self.ic1eq * (a1 as f32)) + (v3 * (a2 as f32));
			let v2 = self.ic2eq + (self.ic1eq * (a2 as f32)) + (v3 * (a3 as f32));
			self.ic1eq = (v1 * 2.0) - self.ic1eq;
			self.ic2eq = (v2 * 2.0) - self.ic2eq;
			let output = match self.mode {
				FilterMode::LowPass => v2,
				FilterMode::BandPass => v1,
				FilterMode::HighPass => *frame - v1 * (k as f32) - v2,
				FilterMode::Notch => *frame - v1 * (k as f32),
			};
			*frame = output * mix.sqrt() + *frame * (1.0 - mix).sqrt()
		}
	}
}

command_writers_and_readers!(
	set_mode: FilterMode,
	set_cutoff: ValueChangeCommand<f64>,
	set_resonance: ValueChangeCommand<f64>,
	set_mix: ValueChangeCommand<Mix>,
);