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use crate::window_size::WindowSize;
use std::{collections::VecDeque, f32::consts::PI, mem};
pub trait WindowFunction: Send {
fn apply(&mut self, data: &mut VecDeque<f32>);
fn reverse(&mut self, data: &mut [f32]);
fn needed(&self) -> usize;
}
pub struct RectangularWindow {
window_size: usize,
}
impl RectangularWindow {
pub fn new(window_size: &WindowSize) -> Self {
Self {
window_size: window_size.inner(),
}
}
}
impl WindowFunction for RectangularWindow {
fn apply(&mut self, _data: &mut VecDeque<f32>) {}
fn reverse(&mut self, _data: &mut [f32]) {}
fn needed(&self) -> usize {
self.window_size
}
}
pub struct HannWindow {
window_size: usize,
function: Vec<f32>,
normalize: Vec<f32>,
previous: Vec<f32>,
previous_overlap: Vec<f32>,
}
impl HannWindow {
pub fn new(window_size: &WindowSize) -> Self {
let window_size = window_size.inner();
let half_window_size = window_size / 2;
let window_size_f32 = window_size as f32;
// 50% overlap
let previous_overlap = vec![0.0; half_window_size];
// with capacity is important for the first needed samples
let previous = Vec::with_capacity(window_size);
let function = (0..window_size)
.map(|n| {
let n = n as f32;
0.5 * (1.0 - f32::cos((2.0 * PI * n) / (window_size_f32 - 1.0)))
})
.collect::<Vec<f32>>();
let normalize = (0..half_window_size)
.map(|i| {
(function[i] * function[i])
+ (function[i + half_window_size] * function[i + half_window_size])
})
.collect::<Vec<f32>>();
Self {
window_size,
function,
normalize,
previous,
previous_overlap,
}
}
}
impl WindowFunction for HannWindow {
fn apply(&mut self, data: &mut VecDeque<f32>) {
let half_window_size = self.window_size / 2;
// the full window size is needed to window over the samples the first time
if self.previous.is_empty() {
// store the latter half for when only half the size is needed
for sample in data.iter().skip(half_window_size) {
self.previous.push(*sample);
}
// apply the function
for (i, sample) in data.iter_mut().enumerate() {
*sample *= self.function[i];
}
return;
}
// In a real time "sliding window" it's necessary to add in the previous samples
// to get the full resolution
for sample in self.previous.iter().rev() {
data.push_front(*sample);
}
self.previous.clear();
// keep this iteration's samples for the next window
for sample in data.iter().skip(half_window_size) {
self.previous.push(*sample);
}
// apply the function
for (i, sample) in data.iter_mut().enumerate() {
*sample *= self.function[i];
}
}
fn reverse(&mut self, data: &mut [f32]) {
let half_window_size = self.window_size / 2;
for (sample, function) in data.iter_mut().zip(self.function.iter()) {
*sample *= *function;
}
// add back in the previous applied window function
// this will reverse the 50% overlap
for (i, (previous, sample)) in self
.previous_overlap
.iter()
.zip(data.iter_mut())
.enumerate()
{
*sample = (*sample + previous) / self.normalize[i];
}
self.previous_overlap.clear();
// copy this window's tail for future overlap
for sample in data.iter().skip(half_window_size) {
self.previous_overlap.push(*sample);
}
}
fn needed(&self) -> usize {
if self.previous.is_empty() {
self.window_size
} else {
self.window_size / 2
}
}
}
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