<?php

$w=300;
$h=400;
$im = imagecreatetruecolor($w, $h);

$white = imagecolorallocate($im, 255, 255, 255);
$black = imagecolorallocate($im, 0, 0, 0);

imagefill($im, 0, 0, $white);

$i=-1;

$i++;
$stages[$i]['name'] = 'Scene 1';
$stages[$i]['x'] = 40; // px
$stages[$i]['y'] = 40; // px
$stages[$i]['L'] = 126; // dB
$stages[$i]['r'] = 5; // m

$i++;
$stages[$i]['name'] = 'Scene 2';
$stages[$i]['x'] = 90; // px
$stages[$i]['y'] = 60; // px
$stages[$i]['L'] = 135; // dB
$stages[$i]['r'] = 3; // m

foreach ($stages as &$stage) {
	$stage['I'] = pow(10,$stage['L']/10)*pow(10,-12);
	$stage['P'] = 4*$stage['I']*pi()*$stage['r']*$stage['r'];
}

function I_from_Pr($P,$r) { if ($r==0) return false; return $P/(4*pi()*$r*$r); }

function dist($x1, $y1, $x2, $y2) { return sqrt(pow(max($x1,$x2)-min($x1,$x2),2)+pow(max($y1,$y2)-min($y1,$y2),2))*20; }

function I2L($I) {return 10*log($I/pow(10,-12)); }

for ($i=0;$i<$w;$i++) {
	for ($j=0;$j<$h;$j++) {
		$I=0;
		foreach ($stages as &$stage) {
			$I += I_from_Pr($stage['P'], dist($i, $j, $stage['x'], $stage['y']));
		}
		$decibels[round(I2L($I))][] = array('x'=>$i,'y'=>$j);
	}
}

/*
header('content-type: text/plain');
print_r(array_keys($decibels));
die();
*/

foreach ($decibels as $dB => $points) {
	$color = imagecolorallocate($im, $dB, $dB, $dB);
	foreach ($points as &$point) {
		imagesetpixel($im, $point['x'], $point['y'], $color);
	}
}

header('content-type: image/png');
imagepng($im);

?>