E-Sheep! They're what computers dream about.

esheep.php

<?// Generate a random image based on a key
$key = sha1(isset($_GET['s']) ? $_GET['s'] : rand());
$WIDTH = isset($_GET['w']) ? $_GET['w'] : 150;
$HEIGHT = isset($_GET['h']) ? $_GET['h'] : 150;

// Globals
$MAX_SAT_LOSS = 0.4;  // 0 - 1.0
$MAX_LUM_SKEW = 0.25; // 0 - 0.5
$COLORS = array();
$IMG = imagecreatetruecolor($WIDTH, $HEIGHT);
if(function_exists('imageantialias')) imageantialias($IMG, true);

// Generate a color from 2-digit hex HSL values
function generateHSL($H, $S, $L){ global $MAX_SAT_LOSS, $MAX_LUM_SKEW, $COLORS, $IMG;
	// Generate the base color values from the hue
	$hue = $H;
	if($hue<43){
		$r = 255;
		$g =   0 + (($hue-0)*255.0/43);
		$b =   0;
	}else if($hue<85){
		$r = 255 - (($hue-43)*255.0/42);
		$g = 255;
		$b =   0;
	}else if($hue<128){
		$r =   0;
		$g = 255;
		$b =   0 + (($hue-85)*255.0/43);
	}else if($hue<171){
		$r =   0;
		$g = 255 - (($hue-128)*255.0/43);
		$b = 255;
	}else if($hue<213){
		$r =   0 + (($hue-171)*255.0/42);
		$g =   0;
		$b = 255;
	}else{
		$r = 255;
		$g =   0;
		$b = 255 - (($hue-213)*255.0/43);
	}

	// Scale the base color values by the saturation
	$sat = 1.0 - $MAX_SAT_LOSS + $S*$MAX_SAT_LOSS/255;
	$r   = 128 + ($r-128)*$sat;
	$g   = 128 + ($g-128)*$sat;
	$b   = 128 + ($b-128)*$sat;

	// Scale the base color values by the luminosity
	$lum = 0.5 - $MAX_LUM_SKEW + $L*$MAX_LUM_SKEW*2/255;
	$r   = ($lum<0.5) ? $r*$lum/0.5 : $r+(255-$r)*($lum-0.5)/0.5;
	$g   = ($lum<0.5) ? $g*$lum/0.5 : $g+(255-$g)*($lum-0.5)/0.5;
	$b   = ($lum<0.5) ? $b*$lum/0.5 : $b+(255-$b)*($lum-0.5)/0.5;

	// Create the color
	$COLORS[] = imagecolorallocate($IMG, $r, $g, $b);
}

// Draw a random shape on the image given one byte of randomness
function drawShape($data, $index){ global $WIDTH, $HEIGHT, $COLORS, $IMG;
	// 1  1  1  1  1  1  1  1
	// -color-  -sh-  -th-  f
	$color = $COLORS[($data>>5) + 1];
	$shape = ($data>>3)%4;
	$thick = ($data>>1)%4 + 2;
	$fill = (bool)($data%2);
	$x = round(((($data*$index)%256)%16)*$WIDTH / 15.0);
	$y = round(((($data*$index)%256)>>4)*$HEIGHT / 15.0);
	$angle = (($data*$index)%256)*2.0*M_PI/255.0;
	$size = (($data*$index)%256)*30.0/255.0 + 20;

	// Depending on the shape, do different drawing things
	imagesetthickness($IMG, $thick);
	switch($shape){
	case 0: // Line
		$rise = sin($angle)*($WIDTH+$HEIGHT);
		$run = cos($angle)*($WIDTH+$HEIGHT);
		imageline($IMG, $x-$run, $y-$rise, $x+$run, $y+$rise, $color);
		break;

	case 1: // Square
		$rise = sin($angle)*$size;
		$run = cos($angle)*$size;
		$points = array(
			$x-$run, $y-$rise
			,$x+$rise, $y-$run
			,$x+$run, $y+$rise
			,$x-$rise, $y+$run
		);
		if($fill){
			imagefilledpolygon($IMG, $points, 4, $color);
		}else{
			imagepolygon($IMG, $points, 4, $color);
		}
		break;

	case 2: // Circle
		if($fill){
			imagefilledellipse($IMG, $x, $y, $size, $size, $color);
		}else{
			imageellipse($IMG, $x, $y, $size, $size, $color);
		}
		break;

	case 3: // Triangle
		$points = array();
		for($a=0; $a<3; ++$a){
			$angle += 2.0*M_PI/3;
			$rise = sin($angle)*$size;
			$run = cos($angle)*$size;
			$points[] = $x-$run;
			$points[] = $y-$rise;
		}
		if($fill){
			imagefilledpolygon($IMG, $points, 3, $color);
		}else{
			imagepolygon($IMG, $points, 3, $color);
		}
		break;
	}
}


// Pick colors based on triad scheme
$h = hexdec(substr($key, 0, 2));
$s = hexdec(substr($key, 2, 2));
$l = hexdec(substr($key, 4, 2));
for($a=0; $a<3; ++$a){
	for($b=0; $b<3; ++$b){
		generateHSL($h, $s, ($l+70*(($b+1)%3-1))%256);
	}
	$h = ($h+85)%256;
}
// Fill with background color
imagefilledrectangle($IMG, 0, 0, $WIDTH, $HEIGHT, $COLORS[0]);


// Draw 17 shapes
for($a=0; $a<17; ++$a){
	drawShape(hexdec(substr($key, $a*2+6, 2)), $a);
}


// Output the image contents
header('Last-Modified: '.date('r', strtotime('-100 years')));
header('Cache-Control: max-age=315360000');
header('Expires: '.date('r', strtotime('+10 years')));
header('Content-Type: image/png');
imagepng($IMG, null, 9);
imagedestroy($IMG);