#!/usr/bin/perl

use warnings;
use strict;

init_dsp(); init_fft();

use Tk;
our $mw = MainWindow->new;
$mw->after(1, \&ticks); # after 1ms, give control back
MainLoop;

sub ticks {
	while (1) {
		render_signal(process_signal(read_dsp()));
		$mw->idletasks();
	}
}


our ($devname, $fmt, $bitrate, $wps, $bps, $bufsize, $dsp);
BEGIN {
	$devname = "default"; # or e.g. hw:1,0 for an additional USB soundcard input
	$fmt = 16;            # sample format (bits per sample)
	$bitrate = 16384;     # sample rate (number of samples per second)
	$wps = 8;             # FFT windows per second (rate of FFT updates)
	$bps = ($fmt * $bitrate) / 8; # bytes per second
	$bufsize = $bps / $wps;   # window buffer size in bytes
}

sub init_dsp {
	open ($dsp, '-|', 'arecord', '-D', $devname, '-t', 'raw', '-r', $bitrate, '-f', 'S'.$fmt) or die "arecord: $!";
	use IO::Handle;
	$dsp->autoflush(1);
}

sub read_dsp {
	my $w;
	read $dsp, $w, $bufsize or die "read: $!";
	return $w;
}


use Math::FFT;
use List::Util qw(sum);

our @freqs;
sub init_fft {
	my $dft_size = $bitrate / $wps;
	for (my $i = 0; $i < $dft_size / 2; $i++) {
		$freqs[$i] = $i / $dft_size * $bitrate;
	}
}

sub process_signal {
	my ($bytes) = @_;

	# Convert raw bytes to a list of numerical values.
	$fmt == 16 or die "unsupported $fmt bits per sample\n";
	my @samples;
	while (length($bytes) > 0) {
		my $sample = unpack('s<', substr($bytes, 0, 2, ''));
		push(@samples, $sample);
	}

	# Perform RDFT
	my $fft = Math::FFT->new(\@samples);
	my $coeff = $fft->rdft;

	# The output are complex numbers describing the exactly phased
	# sin/cos waves. By taking an abs value of the complex numbers,
	# we just measure the amplitude of a wave for each frequency.
	my @mag;
	$mag[0] = sqrt($coeff->[0]**2);
	for (my $k = 1; $k < @$coeff / 2; $k++) {
		$mag[$k] = sqrt(($coeff->[$k * 2] ** 2) + ($coeff->[$k * 2 + 1] ** 2));
	}

	# Rescale to 0..1. Many fancy strategies are possible, this is
	# extremely silly.
	my $avgmag = sum (@mag) / @mag;
	@mag = map { $_ / $avgmag * 0.3 } @mag;
	return @mag;
}


our $canvas;
sub render_signal {
	# Display parameters, tweak to taste:
	my $rows = 2;
	my $hspace = 20;
	my $height = 150;
	my $vspace = 20;

	my @spectrum = @_;
	my $row_freqn = @spectrum / $rows;

	unless ($canvas) {
		$canvas = $mw->Canvas(-width => $row_freqn + $hspace * 2, -height => $height * $rows + $vspace * ($rows + 1));
		$canvas->pack;
	}
	$canvas->delete('all');

	for my $y (0..($rows-1)) {
		for my $x (0..($row_freqn-1)) {
			my $hb = ($height + $vspace) * ($y + 1);
			my $i = $row_freqn * $y + $x;

			# Draw line:
			my $ampl = $spectrum[$i]; $ampl <= 1.0 or $ampl = 1.0;
			my $bar = $height * $ampl;
			$canvas->createLine($x + $hspace, $hb, $x + $hspace, $hb - $bar);

			# Draw label:
			if (!($x % ($row_freqn/4))) {
				$canvas->createLine($x + $hspace, $hb + 0, $x + $hspace, $hb + 5, -fill => 'blue');
				$canvas->createText($x + $hspace, $hb + 15, -fill => 'blue', -font => 'small', -text => $freqs[$i]);
			}
		}
	}

	$mw->update();
}