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//! Window generating functions.
use std::f32::consts;
/// Known window types.
#[derive(Debug,Clone,Copy,PartialEq)]
pub enum WindowType {
/// Simple square window.
Square,
/// Simple sine window.
Sine,
/// Kaiser-Bessel derived window.
KaiserBessel(f32),
}
/// Calculates window coefficients for the requested window type and size.
///
/// Set `half` flag to calculate only the first half of the window.
pub fn generate_window(mode: WindowType, scale: f32, size: usize, half: bool, dst: &mut [f32]) {
match mode {
WindowType::Square => {
for n in 0..size { dst[n] = scale; }
},
WindowType::Sine => {
let param = if half {
consts::PI / ((2 * size) as f32)
} else {
consts::PI / (size as f32)
};
for n in 0..size {
dst[n] = (((n as f32) + 0.5) * param).sin() * scale;
}
},
WindowType::KaiserBessel(alpha) => {
let dlen = if half { size as f32 } else { (size as f32) * 0.5 };
let alpha2 = f64::from((alpha * consts::PI / dlen) * (alpha * consts::PI / dlen));
let mut kb: Vec<f64> = Vec::with_capacity(size);
let mut sum = 0.0;
for n in 0..size {
let b = bessel_i0(((n * (size - n)) as f64) * alpha2);
sum += b;
kb.push(sum);
}
sum += 1.0;
for n in 0..size {
dst[n] = (kb[n] / sum).sqrt() as f32;
}
},
};
}
fn bessel_i0(inval: f64) -> f64 {
let mut val: f64 = 1.0;
for n in (1..64).rev() {
val *= inval / f64::from(n * n);
val += 1.0;
}
val
}
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