lib.rs

use itertools::izip;
use pd_ext::builder::SignalProcessorExternalBuilder;
use pd_ext::external::{SignalProcessor, SignalProcessorExternal};
use pd_ext_macros::external;
use std::ops::Deref;

//based on pan~ from: https://github.com/pure-data/externals-howto#a-signal-external-pan
struct XFadeProcessor {
    //a passive float input, the xfade position
    pos: Box<dyn Deref<Target = pd_sys::t_float> + Send>,
}

impl SignalProcessor for XFadeProcessor {
    //compute the audio
    fn process(
        &mut self,
        _frames: usize,
        inputs: &[&mut [pd_sys::t_float]],
        outputs: &mut [&mut [pd_sys::t_float]],
    ) {
        //read the value of our position setting
        let pos = num::clamp(**self.pos, 0f32.into(), 1f32.into());

        //compute!
        let lpan = 1f32 - pos;
        let rpan = pos;
        for (o, l, r) in izip!(outputs[0].iter_mut(), inputs[0].iter(), inputs[1].iter()) {
            *o = *l * lpan + *r * rpan;
        }
    }
}

external! {
    pub struct XFade;

    impl SignalProcessorExternal for XFade {
        //build the object
        fn new(builder: &mut dyn SignalProcessorExternalBuilder<Self>) -> Result<(Self, Box<dyn SignalProcessor>), String> {
            //2 signal inlets (1 default)
            //1 float inlet (position)
            //1 signal outlet
            builder.new_signal_inlet();
            let pos = builder.new_passive_float_inlet(0f32);
            builder.new_signal_outlet();
            Ok((Self, Box::new(XFadeProcessor { pos })))
        }
    }
}