audio-visualizer 0.2.4

Super basic and simple audio visualization library which is especially useful for developers to visually check audio samples, e.g. by waveform or spectrum. (So far) this library is not capable of doing nice visualizations for end users.
Documentation 
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//! Static spectrum analysis: print to PNG file.

use plotters::prelude::*;
use std::collections::BTreeMap;
use std::path::PathBuf;

pub fn spectrum_static_plotters_png_visualize(
    frequency_spectrum: &BTreeMap<u32, f32>,
    directory: &str,
    filename: &str,
) {
    // assert no NAN
    assert!(!frequency_spectrum.iter().any(|(_, f)| f.is_nan()), "There are NAN-values in the spectrum!");

    // find maximum for graphics scaling
    let mut max = 0.0;
    for (_fr, mag) in frequency_spectrum {
        if *mag > max {
            max = *mag;
        }
    }

    let max_frequency = *frequency_spectrum
        .iter()
        .skip(frequency_spectrum.len() - 2)
        .last()
        .unwrap()
        .0;

    let mut path = PathBuf::new();
    path.push(directory);
    path.push(filename);

    let mut width = frequency_spectrum.len() as u32;
    if width < 700 {
        width = 700;
    }

    let mut height = 700;
    if width < 700 {
        height = (width as f32/0.8) as u32;
    }

    let root = BitMapBackend::new(&path, (width as u32, height)).into_drawing_area();
    root.fill(&WHITE).unwrap();
    let mut chart = ChartBuilder::on(&root)
        .caption("y=f magnitudes of sample", ("sans-serif", 20).into_font())
        .margin(5)
        .x_label_area_size(60)
        .y_label_area_size(60)
        .build_cartesian_2d(
            0.0..(max_frequency as f32), /*.log10()*/
            0.0..max as f32,
        )
        .unwrap();

    chart.configure_mesh().draw().unwrap();

    chart
        .draw_series(LineSeries::new(
            // (-50..=50).map(|x| x as f32 / 50.0).map(|x| (x, x * x)),
            frequency_spectrum
                .iter()
                .into_iter()
                .map(|(frequency, magnitude)| ((*frequency as f32) /*.log10()*/, *magnitude)),
            &RED,
        ))
        .unwrap()
        .label("frequency magnitude")
        .legend(|(x, y)| PathElement::new(vec![(x, y), (x + 20, y)], &RED));

    chart
        .configure_series_labels()
        .background_style(&WHITE.mix(0.8))
        .border_style(&BLACK)
        .draw()
        .unwrap();
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::test_support::TEST_OUT_DIR;
    use std::f32::NAN;

    #[test]
    fn test_visualize_sine_waves_spectrum_plotters() {
        let mut spectrum = BTreeMap::new();
        spectrum.insert(0, 0.0);
        spectrum.insert(10, 5.0);
        spectrum.insert(20, 20.0);
        spectrum.insert(30, 40.0);
        spectrum.insert(40, 80.0);
        spectrum.insert(50, 120.0);
        spectrum.insert(55, 130.0);
        spectrum.insert(60, 140.0);
        spectrum.insert(65, 130.0);
        spectrum.insert(70, 120.0);
        spectrum.insert(80, 80.0);
        spectrum.insert(90, 40.0);
        spectrum.insert(100, 20.0);
        spectrum.insert(110, 5.0);
        spectrum.insert(120, 0.0);
        spectrum.insert(130, 0.0);

        spectrum_static_plotters_png_visualize(
            &spectrum,
            TEST_OUT_DIR,
            "spectrum_60hz_peak_plotters_visualization.png",
        );
    }

    #[allow(non_snake_case)]
    #[test]
    #[should_panic]
    fn test_panic_on_NAN() {
        let mut spectrum = BTreeMap::new();
        spectrum.insert(0, NAN);

        spectrum_static_plotters_png_visualize(
            &spectrum,
            TEST_OUT_DIR,
            "spectrum_60hz_peak_plotters_visualization_NAN.png",
        );
    }
}