avatar-gen.php

<?php

$email = isset( $_GET['email'] ) ? $_GET['email'] : 'null';
$salt = isset( $_GET['salt'] ) ? $_GET['salt'] : '';

// hash email, split it up
$hash = str_split( sha1( $email . $salt ), 2 );

// use first 3 values for foreground
$foreground = "{$hash[0]}{$hash[1]}{$hash[2]}";
// and next 3 values for background
$background = "{$hash[3]}{$hash[4]}{$hash[5]}";

/**
 * Figure out the colors for each square
 */

/*
	This is how we'll mirror. So generate up to half of
	the squares, but round up in case of odd-sized grid

    1 5 5 1   1 4 1
    2 6 6 2   2 5 2
    3 7 7 3   3 6 3
    4 8 8 4
*/

$grid_size = 6;
$middle = ceil( $grid_size/2 ); // round up to capture middle col for odd grids
$gen_up_to = $grid_size*$middle; // calc number of actual squares

$colors = array();
for( $i = 0; $i < $gen_up_to; $i++ ) {

	if ( hexdec( $hash[$i] )%10 < 5 ) {
		$colors[] = $foreground;
	} else {
		$colors[] = $background;
	}

}

/**
 * mirror the design. if odd grid size, exclude the middle column
 */

if ( $grid_size%2 == 0 ) {
	// chunk to maintain symmetry
/* otherwise:
    1 5 8 4   1 4 3
    2 6 7 3   2 5 2
    3 7 6 2   3 6 1
    4 8 5 1
*/
	$mirror = array_reverse( array_chunk( $colors, $grid_size ) );
} else {
	$mirror = array_reverse( array_chunk( array_slice( $colors, 0, $grid_size * ( $middle - 1 ) ), $grid_size ) );
}

foreach( $mirror as $m ) {
	$colors = array_merge( $colors, $m );
}

/**
 * Now actually put the image together
 */

$unit = 100;
$im = imagecreatetruecolor($grid_size*$unit, $grid_size*$unit);

$wpos = 0;
$hpos = 0;

foreach ( $colors as $color ) {

	$color = '0x00'.$color;

	imagefilledrectangle( $im, $wpos, $hpos, $wpos+$unit, $hpos+$unit, $color );
	$hpos += $unit;

	// new col
	if ( $hpos == $grid_size*$unit ) {
		$wpos += $unit;
		$hpos = 0;
	}

}

header( 'Content-Type: image/png' );
header( 'Content-Disposition: filename="avatar.png"' );
imagepng( $im );
imagedestroy( $im );