//! 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 }